HEC-HMS SCENARIOS . ...... Anchusa hispida Forssk. Th. 16. Heliotropium .... HEC-HMS is a freeware model stands for the Hydrologic Engineering Center's.
DEVELOPING RENEWABLE GROUND WATER RESOURCES IN ARID LANDS PILOT CASE: THE EASTERN DESERT OF EGYPT Vegetation Dynamics Assisted Hydrological Analysis for Wady Degla Cairo University
Prepared by
The surface water modeling task group Dr. Mohamed H. El-Gamal, Irrigation & Hydraulics Department - Cairo University Hosam A. A. El- Adawy, Environmental Studies and Researches Institute (ESRI) Project Director, EDP Ahmad Wagdy, Irrigation and Hydraulics Dept, Engineering, Cairo University
EDP- 605- Jul. 2008
DEVELOPING RENEWABLE GROUND WATER RESOURCES IN ARID LANDS PILOT CASE: THE EASTERN DESERT OF EGYPT Vegetation Dynamics Assisted Hydrological Analysis for Wady Degla Cairo University
Prepared by
Hydrological Modeling Task Group Dr. Mohamed H. El-Gamal, Irrigation & Hydraulics Department - Cairo University Hosam A. A. El- Adawy, Environmental Studies and Researches Institute (ESRI) Project Director, EDP Ahmad Wagdy,
Irrigation and Hydraulics Dept, Engineering, Cairo University
Copyright © 2008, UNDP/GEF/Cairo University
EDP- 605- Jul. 2008
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TABLE OF CONTENTS PREFACE.......................................................................................................................... 4 ABSTRACT....................................................................................................................... 4 1. INTRODUCTION ............................................................................................. 6 1.1. GENERAL DESCRIPTION ............................................................................ 6 1.2. BIODIVERSITY OF WADY DEGLA ............................................................ 7 2. GEOLOGICAL SETTINGS ............................................................................ 8 2.1 GENERAL DESCRIPTION ............................................................................ 8 2.2 STRATIGRAPHIC SEQUENCE OF THE AREA........................................ 9 2.2.1 Middle Eocene Rock Units.......................................................................... 9 2.2.2 Upper Eocene............................................................................................. 9 2.2.3 Pliocene Kom El-Shellul Formation......................................................... 11 2.2.4 Armant and Issawia Formation ............................................................... 11 2.2.5 Quaternary Wady Deposists ..................................................................... 11 2.2.6 Recent Nile Sediments............................................................................... 11 2.3 GEOLOGICAL STRUCTURES ................................................................... 11 2.4 LOCAL GEOLOGICAL DESCRIPTION OF WADY DEGLA................ 12 3. HYDROLOGICAL CHARACTERISTICS ................................................. 15 3.1 MAIN DRAINAGE BASINS IN EASTERN DESERT .............................. 15 3.2 HYDROLOGICAL PARAMETERS OF WADY DEGLA......................... 20 3.2.1 General ..................................................................................................... 20 3.2.2 Surface Topography and the Digital Elevation Map................................ 20 3.2.3 Wady Delineation and its Geometric Parameters .................................... 20 4. CLIMATE AND RAINFALL ANALYSIS............................................................... 23 4.1 GENERAL METEOROLOGICAL DESCRIPTION................................. 23 4.2 RAINFALL DATA......................................................................................... 23 4.2.1 Available Rainfall Data ............................................................................ 23 4.2.2 Ground Rain Gauges ................................................................................ 24 4.2.3 TRMM Technique...................................................................................... 26 4.2.4 Analysis of TRMM Data............................................................................ 27 4.3. FREQUENCY ANALYSIS ............................................................................ 30 4.3.1 Frequency Analysis Based on TRMM Data Only ..................................... 30 4.3.2. Frequency Analysis Based on Ground and TRMM Data ......................... 32 4.4. STORM DURATION ..................................................................................... 34 5. VEGETATION OF WADY DEGLA ............................................................ 36 5.1 INTRODUCTION ........................................................................................... 36 5.2 FLORESTIC FEATURES ............................................................................. 37 5.3 HABITAT TYPES........................................................................................... 38 5.4 THREATS........................................................................................................ 39 6. ESTIMATION OF WADY RUNOFF ........................................................... 46 6.1 INTRODUCTION .......................................................................................... 46 6.2 HEC-HMS MODEL....................................................................................... 46 6.2.1 Model Components ................................................................................... 46 6.2.2 Model Input Data...................................................................................... 47 6.3 HEC-HMS SCENARIOS .............................................................................. 47
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6.3.1 Results of Uniform Rain Intensity Case (Scenario#1) .............................. 48 6.3.2 Model Calibration.................................................................................... 49 6.3.3 Results of Spatially Varied Rain Intensity Case (Scenario#2)......................... 51 6.3.4 Consideration of Transmission Losses (Scenario#3) ............................... 57 6.3.5 Comparison and Discussion ..................................................................... 63 7. GROUNDWATER HYDROLOGY .............................................................. 64 7.1 AQUIFER SYSTEM FROM THE REGIONAL SCALE ........................... 64 7.1.1 General Description.................................................................................. 64 7.1.2 Transmissivity and Hydraulic Conductivity.............................................. 65 7.1.3 Storativity of NAS...................................................................................... 67 7.2 RECENT PEIZOMETRIC AND WATER LEVEL PATTERN...................... 67 7.2.1 For NAS System ........................................................................................ 67 7.2.2 For PNAS System...................................................................................... 68 7.3 GROUNDWATER QUALITY ...................................................................... 68 7.4 PRIVIOUS GROUNDWATER MODELING EFFORTS .......................... 69 7.4.1 Regional Resistor-Capacity Model (RC)(1962)........................................ 69 7.4.2 Finite Element Model for the Nubian Aquifer in Egypt (1981) ................ 69 7.4.3 TUB Mathematical Model (1989)............................................................. 70 7.4.4 NSAS Program Regional Mathematical Model (2001) ............................ 70 7.5 GROUNDWATER FLOW MODELING OF FRACTURED CARBONATE AQUIFER .............................................................................. 70 7.5.1 Data Requirement ..................................................................................... 70 7.5.2 Idealized Cross Section Underneath Wady Degla.................................... 71 7.5.3 Unsaturated Flow Modeling ..................................................................... 72 8. VEGETATION DYNAMICS......................................................................... 80 8.1 INTRODUCTION ........................................................................................... 80 8.2 PATCHED VEGETATION PATTERN ....................................................... 80 8.3 SPATIAL VARIATION OF VEGETATION COVER AND DENSITY IN WADY DEGLA ............................................................................................... 82 8.4 VEGETATION PATTERN FORMATION MODELS ............................... 83 9. SUMMARY AND CONCLUSIONS.............................................................. 84 REFERENCES................................................................................................................ 86 BIBLIOGRAPHY OF CHAPTERS 6-8 ....................................................................... 87
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PREFACE This report covers modeling tasks numbers (3) 29-32. These tasks are related to the surface water modeling of wady Degla of the Egyptian Eastern Desert as part of the Eastern Desert Project (EDP).
ABSTRACT The Wady system is an extreme case of a temporary inundated ecosystem in which the duration of flooding is shorter than the dry period (Evenary, 1985). Floods in Saharan Wady systems are scarce; their frequency may be spaced from once every few months to once every decade (Dubief, 1953). A flashflood is a disturbance—a relatively discrete and unpredictable event in time (Resh et al., 1988)—which is capable of disrupting the ecosystem (Pickett & White, 1985), limiting the plant biomass on account of the partial or complete destruction it causes (Grime, 1979). Such disturbance is followed by successive stages of regeneration (Van der Maarel, 1988). The actual state of the vegetation depends on flood frequency and magnitude (Springel et al., 1990; Springel & Sheded, 1991). The Eastern Desert lies between latitude 22 and 29 N covering about 22% of the Egyptian territory and bounded by the Red Sea and Gulf of Suez on the east and the Nile Wady on the west. The Eastern Desert has attracted numerous investments in the last few decades, especially for the tourism and mining ventures. The present water supplies in the Eastern Desert are insufficient, however, to meet the expected increase in water demands for civic, industrial, mining and tourism uses. The Eastern Desert of Egypt contains a huge diversity of ecosystems. The inland part of the Eastern Desert lies between the Red Sea coastal mountains in the east and the Nile Wady in the west, an area of about 223,000km (Abdel Moneim, 2005). It is a rocky plateau dissected by a number of Wadys. Each Wady has a channel with numerous tributaries and the Eastern Desert is divided piecemeal into the catchments areas of these drainage systems. Most of the Wadys drain westward into the Nile. Ground water is believed to be the main source of water throughout the eastern desert area in Egypt. Any development projects for this location should be preceded by a pre-assessment of the available quantity of water in the groundwater reservoir, the groundwater quality and whether this groundwater is renewable or not and how much is the rate of the groundwater replenishment. The main objectives of this study are to identify the boundaries of Wady Degla basin within the Eastern Desert area and to estimate the expected surface flow throughout the Wady system corresponding to different return period. The study also will try to estimate the effective groundwater recharge and it will describe the
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temporal variation of the Wady plantation and its relation with the precipitation over the Wady. Another objective is to develop estimates of the different water-balance terms in the given Wady system and to characterize how much of the precipitation leaves the watershed as evaporation or as in the form of other components of stream flow. Other objectives include the determination of the hot runoff points in the Wady, the places that need to be protected against the probable destructive runoff events and the proposed places of check dams (if any) for any future development.
Wady Degla
Figure 1:
Location of Wady Degla Site within the Context of the Greater Cairo Region
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1.
INTRODUCTION 1.1.
GENERAL DESCRIPTION
Wady Degla lies in the north western bound of the eastern desert. It is extended from the east bound at (30 00 38.9N, 31 39 00.3E) to west bound at (29 51 33.6N, 31 16 14.8E). As it has been mentioned before, Wady Degla drains its water down to the west side up to the Nile river and its outlet is located at 31 16 12E, 29 56 32.6N. Figure 1 presents the location of the Wady within the context of the Greater Cairo region whereas Figure 2 presents the nearby Wadys (Wady Hof and Wady Garawi) to Wady Degla from the south bound.
Figure 2:
Nearby Wadys Adjacent to Wady Degla (After Hamdan, 1999)
The Wady is considered as a part of the northern plateau which is known as a major distinctive geographical environment in Egypt. Wady Degla starts in the form of small tributaries where rainfall water pours on hills surrounding the Wady. Wady Degla is known for its remarkable scenes and biodiversity. The remarkable resources in the Wady Degla are its general scene which is rich in plant and animal life. The Wady is covered with protective permanent plantation layer containing more than 64 kinds of plants. Traces of deers availability were newly recorded in this area as well as 20 kinds of reptiles that include Egyptian turtles, which are endangered of extinction. There
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are also 12 kinds of the eastern desert birds, in addition to kinds of migrating and visiting birds in winter as well as the resident and visiting birds in summer. 1.2.
BIODIVERSITY OF WADY DEGLA
Wady Degla is rich in fossils, including Middle Eocene nummulites and gastropods. The Wady floor and differentially eroded sides clearly show the paths of the rivers that have carved their way through the limestone over millions of years. After a heavy rainstorm, that only occurs once every few years. Recent designation of Wady Degla Protected Area has focused attention on small but remarkably varied caves of phreatic origin, which are the principal expressions of its karstification. One is a typical tubular conduit cave. Another descends steeply to a vertical shaft where initial reconnaissance had to be halted. This karst has been subjected to repeated marine transgressions since onset of speleogenesis. A sequence of partially cemented stratified littoral fills is present in several of these caves, (Halliday, 2003). Figure 2 shows the entrance of one of the bat caves of Wady Degla.
Figure 2:
Example of the Bat Caves of Wady Degla
The steep sides of the Wady protect the unique wildlife found there. The Wady has a group of animals including mammals like deer, taital, mountain rabbits, red fox, feather tailed rat, oviparous, barbed rat, little tailed bat, and others. Among the insects there are many others. 18 species of reptiles have been recorded. There are also 12 kinds of the eastern desert birds, in addition to kinds of migrating and visiting birds in winter as well as the resident and visiting birds in summer. Because of its proximity to Cairo, Wady Degla has been used for many years for quarrying to provide building stone and cement, with the consequent deterioration in environment and habitat. Since 1999, it has been declared a Protected Zone by the Egyptian Government in order to maintain its fragile ecosystem.
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2.
GEOLOGICAL SETTINGS 2.1
GENERAL DESCRIPTION
Figure 3 presents a sketch of the regional geological map of the Northern part of Egypt. It shows that Wady Degla belongs to the Eocene zone.
Wady Degla
Figure 3:
Regional Geological Map Showing the Study Area
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2.2
STRATIGRAPHIC SEQUENCE OF THE AREA
The previous geological studies that have been carried out in the area resulted in establishing the stratigraphical setting of the sedimentary sequence in the area under consideration (refer to the stratigraphic study for Tebbin Thermal Power Plant, 2005) and the structural elements that affected the area during the geologic history. The stratigraphic sequences fall in the study area ranges in age from Eocene to the Quaternary. In the following a brief description will given (refer to Figure 4). 2.2.1 Middle Eocene Rock Units The Mokattam Group in its south and southeastern part at Helwan area interfingers with Helwan Facies of Middle Eocene. It consists of the following two formations from older to younger. Gebel Hof Formation: It is exposed at the base of Gebel Hof and extends northwards to Gebel Toura and exposed at Wady Hof .The maximum thickness is about 120m as recorded by Farag and Ismail (1959) in Gebel Hof who subdivided the formation into two rock units as follows: TOP: Two Nummulitic gizehensis bed. It consists of about 42m of grayish white, slightly chalky, highly fossiliferous with Nummulites sp, Turrietella sp., Natica longa, Cerithium la cheris, The upper 79m is made up of white to yellowish white marly limestone. One poorly fossiliferous limestone with intercalations of some white chalky and marly limestone with Lucina sp. BASE: Observatory Formation: Forming the topmost part of the Middle Eocene section and cover the north and northeastern part and south of Helwan area. It consists of about 77m of white to yellowish white, marly and chalky limestone intercalated with hard, grey dolomitit limestone bands. fossiliferous with Nummulits sp, Ostrea elegans, Pecten sp, Lucina mokattamensis and others. 2.2.2 Upper Eocene The Upper Eocene Maadi Group is subdivided into the following three formations from base to top: • Qurn Formation: It consists of about 70m of highly fossiliferous limestone, chalky, white with marl interbeds at the middle part. • Wady Garawi Formation: It is formed of limestone, marls and shales which represents the topmost part of the carbonate section of the Upper Eocene. The thickness is about 44m. • Wady Hof Formation: It represents the clastic section of the Upper Eocene. It consists of about 22m of sands, fossiliferous calcareous sandstone and clays. The southern outcrops of Wady Hof formation were traced south of Wady Garawi. The maximum thickness is 50m.
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Figure 4:
Geological Map of the Study Area (Sweden, 1990)
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2.2.3 Pliocene Kom El-Shellul Formation The marine Pliocene section is represented by about 2-5 m of yellowish brown, gritty calcareous sandstone with Pectin sp. The section was described under the term Kom ElShellul Formation which is well exposed to the south of Wady Garawi. 2.2.4 Armant and Issawia Formation It is made up of alternating beds of locally derived gravels from Eocene limestone cemented by fine to coarse grain sandstone. The section is friable, yellowish to brownish white colors and extended northward and southward along the Nile Wady in the form of small patchy gravel sheets. The formation was first described by Said (1975) and the age was assigned to the early Pleistocene. 2.2.5 Quaternary Wady Deposists It forms the floor of the Wadys which drains to the Nile. It consists of gravels and boulders from limestone, dolomite and rare cherty materials derived from the local rock units. 2.2.6 Recent Nile Sediments It covers all the area within the Nile Wady as well as the cultivated lands. It is made up of silt and clay with sand interbeds. This is the most fertile cultivated soil. The stratigraphic sequence with a brief lithology of these formations is summarized in Figure x. 2.3
GEOLOGICAL STRUCTURES
Structurally, the area is affected by a number of fractures and normal faults, striking in two main trends in the NW-SE and ENE-WSW directions (refer to Figures 5 and 6).
Figure 5:
Fracture Map of the Study Area Based on the Land sat TM Image
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Figure 6:
Rose Diagrams of the Number Percent and Length Percent of the First and Second Order Fractures for the Four Large Basins in the Nearby-Hood of the Study Area (Wadys: Degla (1), Hof (2), El-Gabow (3), and Garawi (4))
As far the northern part of Egypt is situated on the unstable shelf as described by Said (1962), the study area was affected mainly by the following faulting and folding patterns: a) Faulting Pattern: The area was affected mainly by two system of faulting: - Erytherian trend which extend in a N55oW direction. It is mostly affecting the Eocene limestone plateau. This trend is the younger which affected the older (NE) trend. - Tethyan trend having an E-W direction. It affects the northern part of Gebel Mokattam, Cairo Suez road and Gebel Hof. Generally, all the faults are of normal gravity type. b) Folding System: No folds are visible at the area under consideration. The only fold is seen north and south of Gebel Yahmoum El Asmr and near the Maddi-Kattamiya Road where the fold axis trends in NW-SE direction. 2.4
LOCAL GEOLOGICAL DESCRIPTION OF WADY DEGLA
As it has been mentioned before, Wady Degla is formed in the Eocene limestone pavement that had remained in the marine environment during the Eocene Epoch in the eastern desert (60 million years ago). The exposed outcrops of the Eocene rocks are characterized by fossils of Nummulites gizehensis and the vertical crevices of the exposed bed-rock are filled with blown sand. A hard band of siliceous limestone forming the upper plateau is underlained by further limestones, some of which have been dolomitised, Figure 7. The Wady passes through the limestone rocks. The height of these rocks alongside the Wady is around 50 m. Figure 4 presents a stratigraphic section of Wady Degla.
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Figure 7:
Snapshot of the Wady (Looking Downstream)
Figure 8:
Limestone Bedrock (Wady Degla Formation)
The rain water dropping from the waterfalls affected the limestone rocks along the years and formed the so called canyon Degla, which resembles the Grand Canyon in the U.S., Figure 9.
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Figure 9:
Water-Carved Rock Formation in Degla (Degla Canyon)
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3.
HYDROLOGICAL CHARACTERISTICS 3.1 MAIN DRAINAGE BASINS IN EASTERN DESERT
The Eastern Desert of Egypt is bounded by the Red Sea and the Gulf of Suez from the east, and the River Nile Wady from the west. It lies between latitudes 22o and 29o N and covers an area of about 223,000 km2 forming about 21% of the total area of Egypt. The main Wadys in the eastern deserts can be divided into two main groups. The first group includes all the drainage basins that discharge toward the Red Sea coast whereas the second group includes all the drainage basins that drain toward the Nile basin course. The first group (Red Sea Group) includes about 28% of the eastern desert Wadys whereas the second group (To Nile- Basin Group) includes more than 72% of the whole eastern desert Wadys. Figure 6 presents the Red Sea drainage basin group (shown in red) and the Nile drainage basin group (shown in blue). The aforementioned figure gives a number to every major subcatchment with some more detailed information given in the attached table (Table 1). Figure 10 also presents the study area (marked as zone 1A) with more details of the study area as shown in Figure 11.
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Basin group drains to Nile
1A
Basin group drains to Red Sea
Refer to Fig. 7
Figure 10:
Drainage Basins of Eastern Desert (Modified from El-Shamy, 1992)
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Table 1A:
Nile Basin Drainage Group
# 1A 1A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Basin Name Wadi Degla Wadi Hof Garawi ElHai ElWirga ElNuimya ElQattar Lishyab Sannur ElSheikh Tarfa Imrani Assuti UmmDud Qassab Qena El-Mathula ElSkoki Hegaza Abbad Shait KomOmbo Egyptian Subbasins of WadiAlaqi Subtotal
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L(km) 37 226 95 155 328 205 120 1,593 301 3,886 276 2,492 556 628 6,450 2,685 170 100 1,960 1,600 3,915 2,760 30,538
Area (km2) Comment 260 Fig. 7 Fig. 7 500 Fig. 6 200 Fig. 6 450 Fig. 6 750 Fig. 6 500 Fig. 6 400 Fig. 6 6,500 Fig. 6 900 Fig. 6 11,600 Fig. 6 900 Fig. 6 6,200 Fig. 6 2,100 Fig. 6 2,000 Fig. 6 18,000 Fig. 6 7,700 Fig. 6 300 Fig. 6 180 Fig. 6 6,900 Fig. 6 7,700 Fig. 6 19,100 Fig. 6 12,700 Fig. 6 105,840 71.47 %
Table 1B: # 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49
Red Sea Basin Drainage Group Basin Name Beda Ghewwba Araba ElDakhal Hawashiya Garib Dara AbuHad"S" Mellah Bali ElBaroud Safaga Queh Karim Essel UmGheigh Imbarka Dabur Ghadir UmGamil ElGemal Hamata Lahami AbuDarbaa Rahaba Hodien Shab Ibib Subtotal
L(km) 300 1,247 1,566 315 318 107 584 345 713 252 322 260 466 466 240 280 165 190 185 135 385 160 180 160 250 2,830 340 490 13,251
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Area (km2) Comment 800 Fig. 6 3,100 Fig. 6 4,400 Fig. 6 900 Fig. 6 1,100 Fig. 6 250 Fig. 6 1,600 Fig. 6 950 Fig. 6 1,800 Fig. 6 800 Fig. 6 800 Fig. 6 700 Fig. 6 2,100 Fig. 6 1,400 Fig. 6 800 Fig. 6 900 Fig. 6 700 Fig. 6 190 Fig. 6 600 Fig. 6 350 Fig. 6 1,400 Fig. 6 600 Fig. 6 600 Fig. 6 600 Fig. 6 1,100 Fig. 6 10,300 Fig. 6 1,400 Fig. 6 2,000 Fig. 6 42,240 28.53 %
Figure 11:
Hydrological Map (Zooming of Zone of 1A, Fig. 10)
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3.2
HYDROLOGICAL PARAMETERS OF WADY DEGLA
3.2.1 General Wady Degla lies in the north western bound of the eastern desert. It is extended from the east bound at (30 00 38.9N, 31 39 00.3E) to west bound at (29 51 33.6N, 31 16 14.8E). As it has been mentioned before, Wady Degla drains its water down to the west side up to the Nile river and it drains its water near Tora with an outlet that is located at 31 16 12E, 29 56 32.6N. Figure 9 presents some satellite images for Wady Degla outlet to the Nile River. Wady Degla has different sub branches that include: Wady "Um Rtm", Wady "Um Saad", Wady "Um Sdood", Wady "Qatareef", Wady "Tyb Al-Omrain", Wady Al-Hemarah", Wady "Al-Shbah", Wady "Al-mzylha", Wady "Abu Owaiqylah" and others… (DRTPC, 1983). 3.2.2 Surface Topography and the Digital Elevation Map In order to identify the exact basin boundary, the 90mx90m digital elevation map has been obtained from NASA related web site and converted via TV-Builder converter to the ASCII format which is readable by WMS. Figure 10 presents the DEM of Wady Degla and its related topographical contour lines. It has been shown that the maximum level of the basin is not larger than 600m whereas the minimum level is about 15m at the outlet to the Nile River. 3.2.3 Wady Delineation and its Geometric Parameters Basin delineation of Wady Degla has been carried out using WMS package with the help of TOPAZ subroutine. The maximum stream length of the main Wady is about 46km with a sinuosity of 1.25. The maximum stream slope of the Wady is estimated as 0.9% and the local slope of the Wady exceeds 1.12% in some places near the outlet. The Wady shape is elongated with a large shape factor of 5.39. The total area of the catchment basin is estimated as 260 km2. The maximum Wady level reaches 578m amsl with an average basin elevation of 292.6 amsl. The main Wady is generally wide and could reach a width of 1.0 km in some locations with steep Wady sides rising 50m from the Wady floor. Figure 10 presents the delineation of Wady Degla whereas Table 2 summarizes the geometric parameters of the basin. It should be mentioned that there is a number of industrial building and queries currently located in the outlet reach of Wady Degla. This industrial development is blocking a significant part of the Wady outlet and this condition could render a catastrophic situation in case of low frequent flood event.
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Figure 12:
Satellite Images of the Outlet of Wady Degla to the Nile River
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Figure 13:
Topographical Contour Map of the Study Area Produced from DEM
Nile River
Figure 14: Table 2:
Delineation of Wady Degla Catchment Properties of Wady Degla Property
Value
Catchment Area
259.5 km2
Maximum stream length
46.6 km
Maximum stream slope
0.9%
Average elevation
293 asml
Centroid- stream
68.371 km
distance Shape factor
5.4
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4.
CLIMATE AND RAINFALL ANALYSIS 4.1
GENERAL METEOROLOGICAL DESCRIPTION
The Eastern Desert in general is characterized by its extreme aridity. This sever aridity climate greatly influences the hydrological properties of the drainage basins in the area. The maximum and minimum recorded temperatures in the area are 41C and 21C, while the relative humidity (RH) ranges between 56% and 40%, averaging about 43% in summer and 48% in winter. Generally, the rainfall varies considerably from one season to another. The average annual rainfall ranges between 2.75 mm and about 50 mm at the extreme southeastern zone while sporadic showers are recorded occasionally during winter in some places (Aggour and Sadek 2001) causing flash floods. Based on Helwan rain gauge station, the average annual rainfall is only 13mm. In the last 50 years, floods have been recorded in 1969, 1980, 1984, 1985 and 1994. Even though the amount of rainfall is quite small, floods are the major natural hazard in the Eastern Desert. It is important to mention that the meteorological stations in the Eastern Desert are few relative to the size of the surface area and these stations are mostly distributed along the Red Sea coast and the Nile Wady. Thus, the recorded data from these stations does not reflect the area rain field of the inland areas of the Eastern Desert. The climate of the study area belongs to the arid-meso-mega-thermal type that is characterized by scarce winter rainfall and mild temperature during the rainfall season. The rainfall pattern of the study area is characterized by its scantiness, its seasonality and its inconsistency.
4.2
RAINFALL DATA
4.2.1 Available Rainfall Data The analysis of the available rainfall records from the nearby ground raingauge stations has indicated the sever scarcity of rains over Wady Degla. The nearest rain gauge stations to Wady Degla are Helwan followed by Suez Rain gauge stations. The authors were able to obtain the following rainfall data for the study area: #
Time Scale
Data Type
Period
Time Span (yrs)
Data Source
1
Monthly data
Ground Station
1968-2003
36
Helwan Station
2
Daily data
Ground Station
1904-1982
79
Helwan Station
3
Monthly data
Radar Data
1951-1999
49
TRMM-gridded data
4
Daily data
Radar Data
1998-2007
10
TRMM-gridded data
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4.2.2 Ground Rain Gauges 4.2.2.1 Monthly data Based on the 36-year annual records of the monthly rainfall measurements (from 1968 to 2003) at Helwan station, it has been found that the mean annual rainfall does not exceed 13mm and the maximum daily rainfall (from 1968 to 2003) was 25mm/day. Table 3 summarizes the temperature, humidity and rainfall data at Helwan station whereas Figures 15 and 16 plots the monthly rainfall as a percentage from the mean annual rainfall and the maximum daily rainfall for each month in the year (based on the monthly data set #2 from Helwan station). Table 3:
Month
January February March April May June July August September October November December Annualaverage
Monthly Average Temperature, Humidity and Rainfall Data at Helwan Station (1968-2003).
Av. Monthly Max. 19.1 20.8 24.8 29.1 33.1 35.5 36 35.4 33.8 30.6 25.1 20.4 28.6
Temperature (Co) Av. Highest Monthly Daily Min. Max 7.6 31.4 8.7 34.1 11.6 37.4 15.3 42.6 18.9 47 21.5 45.2 23.2 45.3 23.2 43.4 21.7 44.8 18.6 40 13.6 34.9 9.3 34.4
Lowest Daily Min -2 1.4 2.5 5.6 10.4 14.6 16.5 16.8 13.8 9 4.4 2
16.1
24
Rainfall
Relative Humidity (%)
Total Monthly (mm)
Max in a single day (mm/day)
55 51 46 40 40 42 49 52 51 51 55 55
3.2 2.3 2 0.8 0.4 Trace(2) 0 0 0 0.1 1.5 2.8
13.2 25 10.4 6.1 1.3 Trace 0 0 0 1.9 18.1 13
48.8
13
% of the Mean Annual
30 25 20 15 10 5
Au gu Se st pt em be r O ct o No ber ve m be De r ce m be r
Ju ly
Ju ne
ay M
Ap ril
Ja nu a Fe ry br ua ry M ar ch
0
Month
Figure 15:
Monthly Rainfall as a Percentage From the Mean Annual Rainfall (Helwan, 1968-2003).
25 20 15 10 5
Au gu Se st pt em be r O ct ob er No ve m be De r ce m be r
Ju ly
Ju ne
ay M
Ap ril
0 Ja nu a Fe ry br ua ry M ar ch
Max in a single day (mm/day)
30
Month
Figure 16:
Maximum Daily Rainfall Per Each Month (Helwan, 1968-2003).
4.2.2.2 Daily/Maximum storm data The maximum rainfall data per storm has been also obtained for Helwan Station for the period starting from 1904 to 1982. The almost 80-years long recorded data are totally sufficient to carry out frequency analysis to predict the low-frequent storm events such as the 100-yr event. However this data set suffers from covering rainfall measurements in the last two decades. Based on this ground data set, the maximum rainfall storm recorded
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40 35 30 25 20 15 10 5 0 19 04 19 08 19 12 19 16 19 20 19 24 19 28 19 32 19 36 19 40 19 44 19 48 19 52 19 56 19 60 19 64 19 68 19 72 19 76 19 80
Rainfall Storm Depth (mm)
in the area was the 1908 storm event with a rainfall depth of 38 mm. It has been also noticed that the area is experiencing a general dry-period with an average reduction in maximum storm depth of about 6%, refer to Figure 17.
Time (yrs)
Figure 17:
Maximum Rainfall Storm Depth Measured at Helwan Station (1904-1982)
4.2.3 TRMM Technique Since the number of the available ground raingauges is limited and the gauges are sparsed with large distances in between, the use of other sources of rainfall data renders to be important. Recently, the Tropical Rain Measurement Mission (TRMM) has closed this gab by providing every three hours rainfall measurements over a global 0.25° x 0.25°. Therefore the use of TRMM data will be so valuable for the following: 1. It provides rainfall data at relatively dense and equal grid spacings therefore it will help in enhancing the spatial resolution of the measured rain field. 2. It provides every 3 hours).
continuous
time
series
3. TRMM data are downloadable free including TOVAS web site and many others.
measurements from
different
(one web
record sites
The following subsection gives more details about TRMM data. Tropical Rain Measurement Mission (TRMM) is the first space-borne precipitation radar designed to provide 3D-maps of storm structure. The mission was launched on November 28, 1997. TRMM provides systematic, multi-year measurements of rainfall in the tropics as key inputs to weather and climate research. The satellite
26
observations are measurements to techniques.
complemented by ground frequently validate the
radar and rain gauge satellite rain estimation
The TRMM orbit is circular at an altitude of 350 km and an inclination of 35 degrees to the Equator. It has an orbital duration of 91 minutes which means 16 orbits/day. Each orbit provides extensive coverage in the tropics and the circular coverage allows each location to be covered at a different local time each day. This kind of sampling enables the analysis of the diurnal cycle of precipitation. TRMM data covers almost the whole universe and The estimates are provided on a global 0.25° x 0.25° grid over the latitude band 50° N-S within about seven hours of observation time. The data are available in the following formats: a) Hourly data (accumulated 3 hrs data) (from Jan, 1997 to July, 2007) b) Daily data (from Jan, 1997 to July, 2007) c) Monthly data (from 1978 to 2006, data averaged over 1° x 1° grid boxes and one month.). 4.2.4 Analysis of TRMM Data TRMM daily data as well as monthly data have been downloaded from TOVAS web site for an area larger than the area of Wady Degla basin in order to help in creating better contour mapping. The coordinates of the downloaded area are as follow: (31.3E, 29.6N) and (32E, 30.2N). The downloaded area is discretized into nearly equal grid cells of 0.1 degree in size and of 0.15 degree in spacing. For each cell, the TRMM daily records have been obtained and analyzed to get the statistical characteristics at each cell. The obtained statistical characteristics include: the maximum daily rainfall for each year, the accumulated rain depth along the whole record (1998-2007) and the average number of rainy days and we identified a rainy days as the day that has precipitation depth larger than 0.2mm (which is the same threshold limit for the tipping-bucket raingauge (TBRG) to produce one tip). Figure 18a presents the isohyetal contour lines of the accumulated total rain depth that falls on Wady Degla basin during the period from Jan.1998 to July 2007 (10 years). It has been shown that the total accumulated depth varies from 100 mm in the eastern region of the catchment to more than 400mm in the western region of the catchment near the outlet.
27
Figure 18a:
Isohyets of Accumulated Total Rain Depth from 1998 to 2007 (Based on TRMM Data)
Figure 18b:
Contours of Average No. of Rainy Days (P>0.2mm) from 1998 to 2007 (Based on TRMM Data)
Figure 18b shows the contour lines of the average number of rainy days within the last 10 years. It is shown that the number of rainy days over the low reach is 5 times higher than the number of rainy days over the highland reaches.
28
Figure 19 presents the isohyets of the maximum daily rainfall for the 10 years record. The figure shows (on the contrary of Figure 18) that the maximum daily precipitation takes place at the eastern region of the catchment and the lowest values are recorded at the western region (near the outlet). It has been shown that the maximum daily rainfall over the catchment is about 16mm. The isohyets of the maximum daily rainfall data for the study area (presented in Figure 19) has been normalized to get the dimensionless isohyets of the maximum daily rainfall factor, refer to Figure 20.
Figure 19:
Isohyets of Maximum Daily Rainfall (Based on TRMM Data)
29
Figure 20:
4.3.
Isohyets of Maximum Daily Rainfall Factor (Based on TRMM Data)
FREQUENCY ANALYSIS
Two runs of frequency analysis have been carried out. The first based on the radar TRMM data only (from 1998 to 2007) which reflects the current dry period that is currently dominating the region. The second run integrates the ground rainfall data (79 and the TRMM radar data (the last 10 years) to get longer record reflect the whole temporal rainfall variations in the last 90 years. 4.3.1
run is highly study years) and to
Frequency Analysis Based on TRMM Data Only
A frequency analysis has been performed based on the 10-years TRMM rainfall data despite that the available data is too short to be used for predicting the long term return period events. Figure 21 shows the results of the frequency analysis using HydroFreq software and based on different statistical distribution models including Gumbel distribution (GEV), Three-point Log normal(LN3), Log Peirson distribution (LP) and three-point Log Peirson distribution (LP3). It appears that GEV distribution fits the data reasonably well compared to the other distributions.
30
Table 4:
Results of Rainfall Frequency Analysis for Wady Degla (Based on TRMM Data)
Based on the carried out frequency analysis of the max. daily rainfall data, the maximum 24hrs rainfall data can be deduced by following the recommendations given by WMO. In this study, we obtained the 24hrs maximum rainfall data by multiplying the daily data by an amplification coefficient greater than one. The most common and the widely accepted value is 1.14. Accordingly, the obtained 24hrs max. rainfall data are given in the following Table below:
Table 5:
Design Maximum 24hrs Rainfall Data (Based on TRMM Data Only) RP 2 5 10 20 50 100
Max. Daily (mm) 5.26 8.68 11.44 14.52 19.27 23.49
31
Max. 24hrs(mm) 6.0 9.9 13.0 16.6 22.0 26.8
P(mm/day) Figure 21:
Rainfall Frequency Analysis for Wady Degla Catchment (Based on TRMM Data Only)
(GEV): Gumbel distribution, (LN3): Three-point Log normal, (LP): Log Peirson distribution and (LP3): three-point Log Peirson distribution
4.3.2.
Frequency Analysis Based on Ground and TRMM Data
Since the available ground rainfall data does not cover the storm event in the last two decades, it is expected that such data will tend to overestimate the design storm events required for the different engineering applications due to the general current dominating dryevents. In order to get better predictions and to carryout frequency analysis, it has been decided to merge the 10-years daily available radar data (TRMM data from 1998 to 2007) estimated at the centroid grid of Wady Degla catchment with the 79-years ground data. Before carrying the analysis, the TRMM daily data has been converted to corresponding 24-hrs data using the commonly used transformation factor recommended by WMO and the resulted time span of the extended time series becomes almost 90 years. Figure 22 shows the results of the frequency analysis for the extended time series using HydroFreq software and based on different statistical distribution models including Gumbel distribution (GEV), Three-point
32
P(mm/day)
Log normal(LN3), Log Peirson distribution (LP) and three-point Log Peirson distribution (LP3). It appears that GEV distribution fits the data reasonably well compared to the other distributions.
Figure 22:
Rainfall Frequency Analysis for Wady Degla Catchment (Using the Extended Time Series Data)
(GEV): Gumbel distribution, (LN3): Three-point Log normal, (LP): Log Peirson distribution and (LP3): three-point Log Peirson distribution
Based on the carried out frequency analysis of the max. daily rainfall data, the maximum 24hrs rainfall data can be deduced by following the procedure presented in the previous subsection and accordingly, the obtained 24hrs max. rainfall data are given in the following Tables below (Tables 6 and 7):
33
Table 6:
Results of Rainfall Frequency Analysis for Wady Degla (Based on Ground and TRMM Data)
Table 7:
Design Storm Depth (Based on Ground Station Data and TRMM Data) RP 2 5 10 20 50 100
Ground +TRMM 5.85 10.38 14.09 18.27 24.79 30.66
TRMM only 6.0 9.9 13.0 16.6 22.0 26.8
Table 7 also compares between the frequency results from the two data sets (TRMM data set and the extended data set). It is noticed that the results of the two data sets matches reasonably well for the short return event (i.e. events less than 10 years) however for longer events, significant discrepancies exist with higher values (as high as 13% ) produced from the extended time data series compared with the corresponding results from the TRMM data set alone. 4.4.
STORM DURATION
It is difficult to determine exactly the typical design storm event for the study area since there is no hourly rainfall data available for Helwan raingauge station. In order to get a rough but reasonable estimate of the typical storm durations for the relatively less frequent design return period, the authors analyzed the "every 3 hours" TRMM data of the area for the major storm events that took event in the study area (such as the relatively big event that took place on Feb. 1998). It has been noticed that almost all the storms durations are less than 3 hours. Accordingly the runoff calculations and analysis will be
34
% accumulated depth/storm depth
based on assuming a typical design storm of only 2hours long and the variations of rainfall intensity (for time durations less than one hour) will be assumed to follow the commonly used Bill's typical rainfall intensity rates. Therefore, the following accumulated rainfall distribution will be adopted as the typical design storm for relatively high frequent rainfall events (i.e. less than 50 years), refer to Figure 23. For low frequent rainfall events, the adopted design rainfall pattern is given in Figure 24. 120 100 80 60 40 20 0 0
20
40
60
80
100
120
140
Duration Time (hrs)
% accumulated depth/storm depth
Figure 23:
Adopted Design Rainfall Pattern for Relatively High Frequent Rainfall Events (RP=50 yrs)
35
5.
VEGETATION OF WADY DEGLA 5.1
INTRODUCTION
Egypt is part of the Sahara of North Africa. It has an area of about one million square kilometers, divided into a western part comprising the Western Desert (681000 km²), an eastern part comprising the Eastern Desert (223000 km²) and the Sinai Peninsula (61000 km²). The Nile Basin comprises the Wady in the south (Upper Egypt) and the Delta in the north (Lower Egypt), and forms a riparian oasis (40000 km²); this is the densely inhabited farmlands of Egypt. The climate of Egypt is that of the Arid Mediterranean region, with notable differences between the coastal and inland parts of the country. According to the system applied in the UNESCO map of the world distribution of arid regions (which takes into consideration the degree of aridity, the mean temperature of the coldest and the hottest months of the year and the time of the rainy period relative to the temperature regime) , four major bioclimatic provinces are recognized: (i) The hyperarid province with mild winter and hot summer (mean temperature of the hottest months is 20° - 30° C) includes the Eastern Desert (the area between Lat. 22o N. and Lat. 300 N., except the coastal mountains along the Gulf of Suez) and the southern parts of the Western Desert. Rain is extremely scarce and several years may pass without rain; (ii) The hyperarid province with a cool winter (mean temperature of the coldest months is 0° ~ 10° C) and a hot summer. It includes the mountainous massif of Southern Sinai. Rainfall is less than 30 mm/yr, occasional and unpredictable; (iii) The coastal belt falling under the maritime influence of the Mediterranean Sea. It extends between Rafah and Sallum where the annual rainfall is more than 100 mm (250 mm at Rafah and 150 mm at Alexandria) and the dry period is relatively short (attenuated); and (iv) the sub-coastal belt where annual rainfall ranges between 30-100 mm coupled with a mild winter and a hot summer; the dry period is relatively long (accentuated). A preliminary account is given of the main plant communities of the Eastern and Western Deserts of Egypt, chiefly in the neighbourhood of Cairo. As a rule the communities are closely related to the particular geological formations and topography of the area. The presence or absence of blown sand is very important in determining the type of community that develops. Only in areas where sand occurs (either as dunes, drift, or the sandy matrix of flinty gravel hills) the vegetation is able to develop on the slopes below 700 m.; elsewhere it is confined to grooves, Wadys or depressions where soil moisture is sufficient to support vegetation (Davis 1953).
36
The Eastern Desert has a much richer flora than the Western Desert, due to its greater relief, heavier rainfall, and the larger variety of suitable habitats. The richest communities are those of the first terrace in deep limestone Wadys, and those of hills covered with flinty gravel imbedded in a sandy matrix. Most of the desert associations must be classed as edaphic or biotic climax communities. The Eastern desert of Egypt extends between the Nile Wady and the Red Sea. The whole of this desert is a rocky plateau dissected by a number of drainage systems, each with a main channel and numerous tributaries. These Wadys differ greatly in their water resources. Few of them have semi-permanent water resources, while the majority lake such resources and therefore belonging to extremely dry habitats. On rare occasions, when rainfall occurs, usually happen in sudden torrents that over flow in Wady courses usually originating in mountainous areas in the middle of this desert and flowing eastward or westward until debouching into the Red Sea or Nile Wady, respectively. The geological formations between the Red Sea coast and the mountain range differ from that between the mountain range and the Nile Wady, where they are basement complex in the former while limestone and sandstone in the later (Said 1962). Wady Degla (Declared as protected area in 1999) is located in the North-Eastern Desert (known as the Saharo-Sindian Desert) of Egypt. It is extends along nearly 30 km (35 km by folds) from southern east to northern west between longitudes 31o 19` and 31o 37` and latitudes 29o 53` and 29o 57` with very large slope 10 m/ Km, where it drains from Gabal Abu Shama (578 m a.s.l.) and debouching into Nile Wady (21 m a.s.l.). Wady ElThamah is the extension of Wady Degla which drains from Gabal Abu Shama Wady Degla is a limestone desert which comprises massive Eocene age conveniently, classified into upper and middle Eocene (Said 1990).The middle Eocene series includes various limestone which is the main quarrying beds for building stones and for cement industry. The soil is usually composed of rock waste varying in texture from silt to gravel and boulders. It is often noticed that the Wady bed is covered with layers of fine material alternating with layers of coarse gravels. The alternation of layers of different textures has substantial influences on the water available for utilization by plants. 5.2
FLORESTIC FEATURES
Seventy five species belonging to 31 families were recorded in the Wady Degla. They are represented by 58 perennial and 17 annual species (Table 1). The most represented families Zygophyllaceae, and Brassicaceae.
are
Astraceae,
Chenopodiaiceae,
Poaceae,
Therophytes and Chamaephytes are the most dominating life forms which represented by 17 and 27 species, respectively.
37
Therophytes (Annuals) which appear after rainfall and their life cycles ranges from 6 months to one year, represent 22.7 % of the recorded species. Some of the annual species may remain more than one year if the rainfall is abundant and called potential annuals such as Zygophyllum simplex, Centaurea aegyptiaca, Dipoltaxis harra and Bassia muricata. Chamaephytes have 36 % of the total recorded species of these; Achillea fragrantissima, Anabasis articulata, Anabasis setifera, Artemisia judaica, Capparis spinosa, Deverra tortuosa, Deverra triradiata, , Echinops spinosus, Fagonia arabica, Fagonia mollis, Farsetia aegyptia, Iphiona mucronata, Kickxia aegyptiaca, Pergularia tomentosa, Trichodesma africanum, Zilla spinosa, Reaumuria hirtella, Zygophyllum coccineum, Zygophyllum decumbens and Astragalus spinosus Parasites have three species Cistanche phelypaea, Orobanche cernua and Cuscuta pedicellata 5.3
HABITAT TYPES
According to Kassas and Imam (1954) and Batanouny (1973), the mature Wady bed ecosystem may be subdivided into a number of habitats with respect to grounds of sediment thickness and plant cover. Wady Degla includes several habitats: • Rocky habitat: Gymnocarpos decandrus, stachys aegyptiaca, Farsetia aegyptia and Iphiona mucronata are the dominant species in this habitat. The main associated species are anabasis setifera, Reaumuria hirtella, Fagonia mollis, Erodium glaucophyllum and Diplotaxis harra. •
Cliffs: It is dominated by Capparis spinosa. Limonium pruinosum and cocculus pendulus are the associated species.
•
Terraces: Lycium shawii, Atriplex halimus, Deverra triradiata and Pennisetum divisum are the dominant species. The associated species are Zygophyllum coccineum, Nitraria retusa, Achillea fragrantissima, anabasis setifera, Agathophora alopecuroides, Zilla spinosa, Echinops spinosus, Reaumuria hirtella and Ochradenus baccatus.
•
Wady bed: The most dominant species along Wady Degla is Atriplex halimus and co-dominated with Iphiona mucronata, Ephedra aphylla, Anabasis setifera, Deverra tortuosa, Zilla spinosa and Echinops spinosus in the downstream, with Ochradenus baccatus, Deverra triradiata, Lycium shawii and Farsetia aegyptia in the middle stream and with Retama raetam Anabasis articulata and Tamaria aphylla in the upstream. The associated species are Achillea fragrantissima, Fagonia mollis, Fagonia arabica, Heliotropium arbainense and Launaea nudicaulis.
•
Degla canyon: the most characteristic species are Tamarix nilotica, Phragmites australis and Capparis spinosa. The associated species are Fagonia mollis, Iphiona mucronata and anabasis articulata. Bir Degla (Latitude 29° 56` 19`` N and Longitude 31° 25` 21``E) has 1.9 m diameter and 0.7 m depth and filled by water
38
after rainfall. Capparis spinosa and Zygophyllum coocineum seedlings appear after drying the Bir. Vegetation of the Wadys in the eastern desert is distinguished into plant communities where the dominant perennial species give the permanent character of plant cover in each habitat. This may be attributed to the rather scanty rainfall which is not adequate for appearance of many annuals. 5.4 -
-
THREATS presence of garbage recycling center near the middle stream and flying the plastic bags until it surrounds the plants and affect the rate of growth Building sandy dams (1.2 -1.6 m height) by Arabs for cultivate some plant. Overgrazing in Wady El- Thamah (The upstream of Wady Degla that drains from Gabal Abu Shama) which is not conserved area. Presence of Kattamiya Cement Factory in the upstream of Wady Degla which affects in two ways, firstly, the pollution of the area by fine cement dust particles affecting the plants, secondly, remove the soil surface and putting white powder excluded from cement industry. Bad behaviour of some visitors such as burning some plants, running over plants by their cars, … etc.
Table 8: No.
The Life Forms of the Recorded Species in the Study Area According to Raunkiaer`s System (1934). Life Species Form
1
Aizoaceae
1
Mesembryanthemum forsskaolii Hockst. ex Boiss.
2
Asclepiadaceae
2
Pergularia tomentosa L.
3
Astraceae
3 4 5 6 7 8 9 10 11 12 13 14
Achillea fragrantissima (Forssk.) Sch. Bip. Atremisia judaica L. Centaurea aegyptiaca L. Echinops spinosus L. Ifloga spicata (Forssk.) Sch. Bip. Subsp. spicata Iphiona mucronata (Forssk.) Asch.& Schweinf Launaea nudicaulis (L.) Hook. f. Nauplius graveolens (Forssk.) Wiklund subsp. graveolens Phagnalon barbeyanum Asch.& Schweinf. Reichardia tingitana (L.) Roth Senecio glaucus (Maire) C. subsp. coronopifolius Volutaria lippii (L.) Cass. ex Maire
Th Ch
39
Ch Ch H Ch Th Ch H H Ch Th Th Th
4
Boraginaceae
15 16 17
Anchusa hispida Forssk. Heliotropium arbainense Fresen. Trichodesma africanum (L.) R. Br.
5
Brassicaceae
18 19 20 21 22
Diplotaxis acris (Forssk.) Boiss. Diplotaxis harra (Forssk.) Boiss. subsp. harra Farsetia aegyptia Turra subsp. aegyptia Pseuderucaria clavata (Boiss. & Reut.) O. E. Schulz subsp. clavata Zilla spinosa (L.) Prantl subsp. spinosa
6
Capparaceae
23
Capparis spinosa L. var. spinosa
7
Caryophyllaceae
24 25 26 27
Gymnocarpos decandrus Forssk. Gypsophila capillaris (Forssk.) C. Chr. capillaris Pteranthus dichotomus Forssk. Spergularia diandra (Guss.) Boiss.
8
Chenopodiaceae
28
Ch
29 30 31
Agathophora alopecuroides (Delile) Fenzl ex Bunge var. alopecuroides Anabasis articulata (Forsssk.) Moq. Anabasis setifera Moq. Atriplex halimus L.
32 33 34
Atriplex leucoclada Boiss. var. inamoena (Allen) Zohary Seidlitzia rosmarinas Bunge ex Boiss. Traganum nudatum Delile
Ch H Ch
9
Cistaceae
35
Helianthemum kahiricum Delile
10
Cuscutaceae
36
Cuscuta pedicellata Ledeb.
11
Ephedraceae
37
Ephedra aphylla Forssk.
12
Geraniaceae
38
Erodium glaucophyllum (L.) L’ Hér.
13
Labiatae
39
Stachys aegyptiaca Pers.
14
Leguminosae
40
Alhagi graecorum Boiss
Th Ch Ch Th H Ch Th Ch Ch Ch H Th Th
Ch Ch N.ph
Ch P N.ph H H H
40
41 42 43
Astragalus spinosus (Foarssk.) Muschl. Retama raetam (Forssk.) Webb& Berthel. subsp. raetam Trigonella stellata Forssk.
15
Malvaceae
44
Malva parviflora L.
16
Menispermaceae
45
Cocculus pendulus ( J. R. & G. Forst.) Diels
17
Nitrariaceae
46
Nitraria retusa (Forssk.) Asch.
18
Orobanchaceae
47 48
Cistanche phelypaea (L.) Cout. Orobanche cernua Loefl.
19
Palmae
49
Phoenix dactylifera L.
20
Peganaceae
50
Peganum harmala L.
21
Plantaginaceae
51
Plantago ovata Forssk.
22
Plumbaginaceae
52
Limonium pruinosum (L.) Choz. Var. pruinosum
23
Poaceae
53 54 55 56 57 58
Bromus madritensis L. Cynodon dactylon (L.) Pers. Desmostachya bipinnata (L.) Stapf Pennisetum divisum (Forssk. ex J. F. Gmel.) Henrard Phragmites australis (Cav.) Trin. ex steud. subsp. australis Schismus arabicus Nees
24
Polygonaceae
59
Rumex vesicarius L.
25
Resedaceae
60
Ochradenus baccatus Delile
26
Rutaceae
61
Haplophyllum tuberculatum (Forssk.) Juss.
27
Scrophulariaceae
62 63
Kickxia aegyptiaca (L.) Nábelek subsp. aegyptiaca Scrophularia deserti Delile
28
Solanaceae
64
Lycium shawii Roem. & Schult.
Ch N.ph Th Th Ph Ph P P Ph H Th H Th G G H. H.H Th Th N.ph Ch Ch H Ph
41
29
Tamaricaceae
65 66 67
Reaumuria hirtella Jaub.& Spach var. hirtella Tamarix aphylla (L.) H. Karst. Tamarix nilotica (Ehrenb.) Bunge
30
Umbelliferae
68 69
Deverra tortuosa (Desf.) DC. Deverra triradiata Hochst. ex Boiss.
31
Zygophyllaceae
70 71 72 73 74 75
Fagonia arabica L. var. arabica Fagonia bruguieri DC. Fagonia mollis Delile Zygophyllum coccineum L. Zygophyllum decumbens Delile Zygophyllum simplex L. Legend Ch: Chamaephyte (Subshrubs) G: Geophyte (Perenial grasses) H: Hemi-cryptophyte (Perenial herbs) H.H: Hydrophyte & Helophyte N.ph: Nano-phnerophyte (Shrubs) P: Parasite Ph: Phanerophyte (Trees) Th: Therophyte (Annuals)
42
Ch N.ph N.ph Ch Ch Ch H Ch Ch Ch Th
Figure 25:
Upstream Part of Wady Degla. Tamarix aphylla is a Large Tree.
Figure 26:
Cappari Spinosa Growing on the Cliffs (About 20 – 30 m Height from Wady Bed).
43
Figure 27:
The Most Higher Part of Wady Degla (Wady El-Thamah). Anabasis Articuata and Retama Raetam are the Dominant Species.
Figure 28:
Gabal Abu Shama Appears in the Background. This Part the Second Higher Point in the Upstream of the Wady. Atriplex Halimus Appears in this Part.
44
Figure 29:
Seedlings of Annual Species Appeared After Rainfall.
Figure 30:
Sandy Dam Appears on the Left Side. Arabs (Site dwellers) are Building it for Reserving Water After Rainfall for Cultivation and Cattle Grazing.
45
6.
ESTIMATION OF WADY RUNOFF 6.1
INTRODUCTION
In order to estimate the expected runoff for different storm event, rainfall-to-runoff technique should be selected. The common practice is to adopt the Rational method for small basin areas which are less than 1.0km2 and to adopt the unit-hydrograph approach for the basins of catchment areas greater than the stated area limit. Since the area of Wady Degla is significantly higher than 1.0 km2, the UH-technique will be applied. In order to calculate the runoff volume and to estimate the outlet hydrograph, HEC-HMS model has been chosen for this regard. The following sub-section introduces the model and its main input data. 6.2
HEC-HMS MODEL
HEC-HMS is a freeware model stands for the Hydrologic Engineering Center’s Hydrologic Modeling System. The model is developed by the US-Army Corps of Engineers to simulate the precipitation-runoff processes of dendritic watershed systems. It is designed to be applicable in a wide range of geographic areas for solving a broad range of problems. This includes large river basin water supply and flood hydrology to small urban or natural watershed runoff. Hydrographs produced by the program can be used directly or in conjunction with other software for studies of water availability, urban drainage, flow forecasting, future urbanization impact, reservoir spillway design, flood damage reduction, floodplain regulation, wetlands hydrology, and systems operation. 6.2.1 Model Components HMS model components include: - basin module, - meteorological module, - control specifications module, and - Input data module. A simulation calculates the precipitation-runoff response in the basin model given input from the meteorological model. The control specifications define the time period and time step of the simulation run. Input data components, such as time-series data, paired data, and gridded data are often required as parameter or boundary conditions in basin and meteorological modules.
46
6.2.2 Model Input Data The model requires different data entries including catchment properties and subsurface losses and soil data, meteorological and rainfall data in addition to control specification data. In order to run the model, the following approaches have been selected: - SCS- Curve number has been used to estimate the watershed and basin losses. Based on the SCS-CN tables available in the literature, the soil surface of Wady Degla is classified as Type B and thus its corresponding CN ranges between 70 to 85. - SCS-UH approach has been selected for rainfall-to runoff transformation; - The lag time has been estimated as 0.6 Tc, where Tc is the time of concentration and Tc is calculated based on Kirpich equation using SMADA Tc- Calculator (as shown in Figure 31.
Figure 31: -
6.3
SMADA Tc Calculator
The SCS-type 2 storm pattern has been adopted for all the analysis since there is no long-record of short-duration rainfall readings available to deduce the actual design storm pattern. It should be mentioned the same storm pattern is commonly used in different flood protection engineering applications including the drainage of the new Cairo international airport and many other projects. HEC-HMS SCENARIOS
Two main scenarios have been considered in the hydrologic modeling. The first scenario deals with the whole catchment as one unit and it assumes that the precipitated rain is uniformly distributed over the whole catchment. On the other hand, the second scenario considers the spatial variations of the precipitated rainfall and it divides the whole catchment into a number of sub basins. For each scenario, five runs have been conducted (run #1 for CN =70, run #2 for CN=75, run #3 for CN =80, run #4 for CN=85 and run #5 for CN=90). For each run, 10 rainfall cases have been considered (starting from rainfall
47
intensity of 5mm and ending at rainfall intensity of 50mm with an incremental step of 5mm). 6.3.1 Results of Uniform Rain Intensity Case (Scenario#1) In this scenario and as it has been mentioned before, the catchment is dealt with as one basin and rainfall is assumed uniform throughout the whole basin. Tables 9 and 10 summarize the results of the simulation. Table 9 and Figure 32 present the expected peak runoff value for each rainfall loading case and for each CN value whereas Table 10 and Figure 33 show the runoff coefficient for each case and Figure 34 gives the expected runoff hydrograph for a uniform rainfall depth of 25mm taking CN= 85. Table 9:
Estimated Peak Discharge for Different Rainfall Intensity and CN Value I(mm)
CN 70 75 80 85 90
15 0 0 0.7 3.9 14.1
20 0 1 4.4 12 32.4
Qpeak(m 3/s)
200 150
25 0.9 4.5 10.2 26 55.7
30 4 9.1 21.1 45 82.6
CN=70
CN=75
CN=80
CN=85
35 8.2 16.7 35.5 65.7 112.1
40 13.2 28.1 52.9 89.9 143.5
45 21.5 42.2 72.8 116.4 176.2
50 32.6 58.5 95 144.7 210
CN=90
100 50 0 10
15
20
25
30
35
40
45
50
Precipitation (mm)
Figure 32:
Peak Runoff Flow as a Function of Max Daily Precipitation Depth and Curve Number (Scenario#1)
Table 10:
Estimated Runoff Coefficient (%) for Different Rainfall Depths and CN Values I(mm)
CN 70 75 80 85 90
15 0.0 0.0 0.5 4.8 15.5
20 0.0 0.6 3.8 10.9 24.2
25 0.4 2.8 8.0 16.9 31.5
30 1.9 5.8 12.3 22.1 37.6
48
35 4.1 9.1 16.6 27.3 42.8
40 6.5 12.4 20.5 31.8 47.2
45 9.1 15.5 24.2 35.7 50.9
50 11.6 18.6 27.6 39.2 54.2
Runoff Coeff. (%)
60.0 50.0 40.0
CN=70
CN=75
CN=80
CN=85
CN=90
30.0 20.0 10.0 0.0 10
15
20
25
30
35
40
45
50
Precipitation (mm)
Figure 33:
Runoff Coefficient (Scenario #1)
Peak Runoff (m3/s)
30 25 20 15 10 5 0 0.00
10.00
20.00
30.00
40.00
50.00
60.00
Time (hrs)
Figure 34:
Sample of Outlet Hydrograph (Scenario #1, CN=85, I=25mm)
6.3.2 Model Calibration The model results presented in the previous chapter has shown significant dependence on the used value of the curve number. Therefore, accurate prediction of runoff values are highly related to the level of uncertainty in the used Curve Number. Model calibration requires runoff flow measurements which are not available. Therefore, the model's parameter is calibrated based on similar experiences in other Wadys and from the reconnaissance visits that have been carried out by the research group. Similar studies in Wady Al-Arish in Sinai have shown that the typical CN value for limestone soil is about 94. Since Wady Degla catchment has many fractures, it is expected that the typical CN value in Degla is less than the aforementioned number.
49
Analysis of runoff flow near the Wady outlet has shown that using CN value of 90 produces water depth at the outlet in the order of 0.5m depth for the highest rain storm that took place in 1998 which seems to be reasonable. However, adopting CN=90 for the commonly high frequent events (Return Periods=10 yrs). Based on the adopted model parameters, the design peak runoff for different return periods has been calculated for CN= 85 and CN=90 and presented in Table 11 and Figure 35.
100 yr
50 yr 20 yr 10 yr
Figure 35a:
Outlet Hydrographs for Different Return Periods (Scenario #1, CN=85)
100 yr
50 yr 20 yr 10 yr
Figure 35b:
Outlet Hydrographs for Different Return Periods (Scenario #1, CN=90, Based on TRMM Data Only)
50
100 yr
50 yr 20 yr 10 yr
RP
2 5 10 20 50 100
Figure 35c:
Outlet Hydrographs for Different Return Periods (Scenario #1, CN=90, Based on TRMM + Ground Data)
Table 11:
Estimated Peak Discharge for Different Rainfall Intensity (Uniform Precipitation Scenario)
Storm Depth(mm) Based on Based on Ground+ TRMM data TRMM data only only 6 5.85 9.9 10.38 13 14.09 16.6 18.27 22 24.79 26.8 30.66
Qpeak (m3/s) Based on TRMM data only(CN =85)
Based on TRMM data only(CN =90)
Based on Ground+ TRMM data (CN=90)
0 0.2 2.2 5.6 17.1 32.1
0.05 2.9 8.6 19.3 41.2 65
0 3.4 11.4 25.4 54.6 86.4
6.3.3 Results of Spatially Varied Rain Intensity Case (Scenario#2) In this scenario, Wady Degla catchment is divided into seven sub-catchments. The methodology of division is based on trying to have sub-catchments with more or less uniform spatial precipitation throughout each sub-catchment. The geometric as well as the hydrologic parameters of each sub-catchment have been obtained using WMS package. Figures 33 and 34 present the 7 identified sub-catchments and their main streams over layered by the layer of Isohyets of maximum daily rainfall factor (shown before in Figure 19).
51
Table 12 summarizes the geometric as well as the hydrological parameters of the seven sub-catchments. It also lists the time of concentration and the time lag for each subcatchment. Table 12 also shows the local average maximum daily rainfall factor for each sub-catchment.
12B 11B 14B
13B
16B 15B
Figure 36:
Wady Degla Sub-Catchments
Figure 37:
Sub-Catchment Streams of Wady Degla
52
17B
Table 12:
Properties of Different Sub-Catchments (Scenario#2)
SubBasin A (km2) S a s AVEL(m) L(km) Smax Tc(min) TL(min) CSD (km) Rfi
11B 90.7 0.063 3.170 1.17 181.4 19.8 0.0144 202.7 121.6 11.4 0.6
12B 20.5 0.042 3.090 1.06 29669.0 8.4 0.0213 90.1 54.1 3.8 0.6
13B 28.3 0.050 2.110 1.35 279.4 10.4 0.0130 128.4 77.0 5.3 0.6
14B 34.3 0.032 1.670 1.23 332.2 9.3 0.0110 125.7 75.4 4.6 0.8
15B 19.5 0.043 3.540 1.07 343.9 8.9 0.0138 111.3 66.8 5.5 0.8
16B 14.2 0.034 2.220 1.13 388.2 6.3 0.0120 90.0 54.0 3.2 0.8
17B 52.0 0.043 2.160 1.23 421.0 13.0 0.0067 196.8 118.1 7.0 0.8
Ai*Rfi (km2)
56.2
12.3
17.0
25.7
14.6
11.6
42.9
For the purpose of comparing the results of Scenario 1 and Scenario 2, it has been assumed that the rainfall volume over the whole catchment is the same however, the spatial distribution is constant (i.e. uniform) for Scenario 1 whereas it is variable from sub-catchment to the other for Scenario 2. Accordingly, the equation that defines the local value of the rainfall intensity (Ii) for each sub-catchment (i) has been deduced as follow:
I i = α .R fi .I u
α=
At
∑ A .R i =1
Where: Ii = Iu = Ai = At = Rfi = n =
(1)
n
i
fi
local rainfall intensity over sub-catchment No. i; the uniform rainfall intensity over the whole catchment (as per scenario 1); the area of the sub-catchment No. i; the total area of the whole catchment; the local average maximum daily rainfall factor for each sub-catchment; number of sub-catchments (7 sub-catchments as per scenario 2).
Table 13 presents the local rainfall intensity Ii for each sub-catchment, i, corresponding to a uniform intensity of the whole catchment Iu.
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Table 13: Iu(mm) 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0
Figure 38:
Local Intensities Over Each Sub-Catchment (scenario2) 11B
12B
13B
14B
15B
16B
17B
4.5 8.9 13.4 17.8 22.3 26.8 31.2 35.7 40.1 44.6
4.3 8.6 13.0 17.3 21.6 25.9 30.2 34.5 38.9 43.2
4.3 8.6 13.0 17.3 21.6 25.9 30.2 34.5 38.9 43.2
Ii(mm) 5.4 10.8 16.2 21.6 27.0 32.4 37.8 43.2 48.6 54.0
5.4 10.8 16.2 21.6 27.0 32.4 37.8 43.2 48.6 54.0
5.9 11.7 17.6 23.5 29.3 35.2 41.0 46.9 52.8 58.6
5.9 11.9 17.8 23.7 29.7 35.6 41.6 47.5 53.4 59.4
Schematic Presentation of Main Basin Elements (Scenario #2)
54
Table 14:
Local Rainfall Depth (Over Each Sub-Catchment) Corresponding to Different Return Periods (Scenario#2)
RP
Iu(mm)
11B
12B
100 50 20 10 5 2
30.66 24.79 18.27 14.09 10.38 5.85
27.4 22.1 16.3 12.6 9.3 5.2
26.5 21.4 15.8 12.2 9.0 5.1
Sub-Catchment# 13B 14B 15B Ii(mm) 26.5 33.1 33.1 21.4 26.8 26.8 15.8 19.7 19.7 12.2 15.2 15.2 9.0 11.2 11.2 5.1 6.3 6.3
Figure 39:
Runoff Hydrographs for Each Sub-Catchment, 100 yr, (Scenario#2)
Figure 40:
Outlet Hydrograph, 100 yr, (Scenario#2)
55
16B
17B
36.0 29.1 21.4 16.5 12.2 6.9
36.4 29.4 21.7 16.7 12.3 6.9
Figure 41:
Runoff Hydrographs for Each Sub-Catchment, 50 yr, (Scenario#2)
Figure 42:
Outlet Hydrograph, 50 yr, (Scenario#2)
Table 15:
Peak Discharge for Each Basin (Scenario#2)
RP
Qout(m3/s)
11B
12B
100 50 20
213.8 135.7 57.70
79.6 51.9 25.5
33.5 21.8 10.6
56
Sub-Catchment# 13B 14B 15B Ii(mm) 30.1 37.1 15.5 19.2 23.7 9.2 8.8 10.8 3.7
16B
17B
13.3 7.9 3.1
24.8 14.7 6.0
6.3.4 Consideration of Transmission Losses (Scenario#3) In this scenario, the assumptions will be the same as that of Scenario #2 except for the consideration of the transmission losses that might take place in the conveying streams.
Transmission losses take place when stream-flow percolates deeply and gets lost underneath. Based on previous studies in arid zones, it is believed that transmission losses account for marked reduction in flow volumes over the reached desert streams (Ecology of Desert Systems By Walter G. Whitford). For example, Mabbutt (1977) reported that transmission losses could decrease the runoff volume by 60 to 65%. Different empirical formulas are found in the literature to estimate the transmission losses from ephemeral streams. However, non of the available equations is universal and therefore, the common practice is to use different approaches to get an estimate of the expected range of the actual infiltration rate then to select the most probable range of the transmission losses based on the awareness of the local conditions. One method commonly used to estimate the infiltration losses in unlined perennial channels is based on Darcy seepage formula, where the gradient of the piezometric is assumed equal to one (the unit gradient approach) and the seepage rate is calculated based on the following relation: QsLoss = K(B+2D) Where: QsLoss K B D
= = = =
(2)
the seepage loss rate (m3/s/m'); the hydraulic conductivity (m/s); the channel bed width (m); the average channel water depth (m).
It should be mentioned that the term in brackets represents the length of the witted perimeter of the channel through which infiltration takes place. It should be also mentioned that the above equation gives the highest estimate of water seepage losses since it assumes that the ground water table is located deep enough from the ground surface. In case of Wady Degla, the deep groundwater level assumption is relevant. One should also mention that the above equation is for perennial channels only and its application to ephemeral streams is questionable and requires special investigation and calibration campaign. The transmission losses will be considered by calculating the expected infiltration losses from the stream channels in Wady Degla. The schematic layout of Wady Degla includes 6 main streams (called hereafter as conduits, refer to Figure 38). The geometric parameters of each stream (conduit) are listed in Table 16.
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Table 16:
Geometric Parameters of Different Stream Conduits Reach# 1 2 3 4 5 6
L(m) 3100 1860 3000 1920 11150 11750
w(m) 2.7 2.0 7.3 2.0 17.4 7.5
So 0.006833 0.00987 0.007979 0.011134 0.011943 0.010045
6.3.4.1 Transmission losses for 20-yr storm event (Scenario#3-Run11) In this run, HEC-HMS package has been used to estimate the outlet hydrograph after the consideration of the transmission losses in the channel streams for the 20-yr storm event. The rate of transmission losses have been evaluated based on Eq. 2 for different hydraulic conductivity values.
Figure 43:
Transmission Losses Rates for Each Conduit, 20 yr, (Scenario#3) (Transmission Losses Based on Eq. 2, K= 1m/day)
58
Figure 44:
Outlet Hydrograph, 20 yr, (Scenario#3) (Transmission Losses Based on Eq. 2, K= 1m/day)
Figures 43 and 44 present the time variations of the transmission losses rates and the outlet hydrograph respectively for the case of K equals 1 m/day. It is of interest to note that conduits No. 5 and 6 produced almost no outflow and thus the source of the produced outflow comes mainly from the direct contribution of the nearest sub-basin (B11) to the Wady outlet (refer to Figure 38). Table 16 lists the transmission losses volume and the peak loss rates for each channel reach. Table 17:
Estimated Transmission Losses for Conduits (Based on Eq. 2, Scenario#3, 20Yrs storm) Reach# 1 2 3 4 5 6 Total(m3)
TransLoss(m3) 30216 6336 117588 12282 438894 138264 743580
QTLpeak(m3/s) 0.7 0.2 2.5 0.4 25.2 9.2
For higher values of K, it is expected that the transmission losses significantly increased in the upper-Wady streams (Wady reach #1, 2 and 4) and this rise will cause the downstream runoff water to decrease and thus the water volume lost downstream will significantly decrease compared to the upstream reaches. 6.3.4.2 Transmission losses for 50-yr storm event (Scenario#3-Run12) This run is the same as run 11 (item 6.3.4.1) except for it is designated for the 50-yr storm event.
59
Figure 45:
Transmission Losses Rates for Each Conduit, 50 yr, (Scenario#3) (Transmission Losses Based on Eq. 2, K= 1m/day)
Figure 46:
Outlet Hydrograph, 50 yr, (Scenario#3) (Transmission Losses Based on Eq. 2, K= 1m/day)
Figures 45 and 46 present the time variations of the transmission losses rates and the outlet hydrograph respectively for the case of K equals 1 m/day.
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Table 18:
Estimated Transmission Losses for Conduits (Based on Eq. 2, Scenario#3, 50Yrs storm) Reach# 1 2 3 4 5 6 Total(m3)
TransLoss(m3) 39528 10398 139878 17676 969216 221472 1398168
QTLpeak(m3/s) 0.9 0.3 3.1 0.5 46.6 11
6.3.4.3 Transmission losses for 100-yr storm event (Scenario#3-Run13) This run is the same as runs 11 and 12 (items 6.3.4.1 and 6.3.4.2) except for it is designated for the 100-yr storm event.
Figure 47:
Transmission Losses Rates for Each Conduit, 100 yr, (Scenario#3) (Transmission Losses Based on Eq. 2, K= 1m/day)
Figure 48:
Outlet Hydrograph, 100 yr, (Scenario#3) (Transmission Losses Based on Eq. 2, K= 1m/day)
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Figures 47 and 48 present the time variations of the transmission losses rates and the outlet hydrograph respectively for the case of K equals 1 m/day. Table 19:
Estimated Transmission Losses for Conduits (Based on Eq. 2, Scenario#3, 100Yrs storm) Trans Loss(m3)
Reach# 1 2 3 4 5 6 Total(m3)
Figure 49:
Eq(2) 48198 11484 159570 20040 1349010 292968 1,881,270.00
Lane 61371 11158 172491 21202 775953 220749 1,262,923.02
Walter 609779 165459 228981 401635 332587 239384 1,977,823.98
Wheater 17375 7151 19173 9575 81776 46136 181,186.42
QTLpeak(m3/s) 1.2 0.4 3.6 0.6 51 12.4
Transmission Losses Comparison Based on Different Approaches, 100 yr, (Scenario#3, K= 1m/day)
Table 19 compares the water volume of the transmission losses for each Wady reach in case of the 100-yr event and using different methods. The compared methods include Eq.(2), Lane, Walter and Wheater empirical formulas. It is clear to note that each method gives different estimate of the transmission losses and it is not possible to say that one of these methods is superior over the others. Figure 49 shows that the transmission losses based on Eq.(2) are generally higher than the results from the other formulas on the contrary Wheater's formula seems to give the lowest predictions. It is also noted that results based on Eq.(2) and Lane's formula are relatively close to each other.
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6.3.5 Comparison and Discussion In this chapter, the authors carried out the hydrological analysis based on two different approaches. The first approach is the conventional one and the more easy to follow where the whole Wady is being dealt with as a single basin. This approach disregard the differences in the infiltration rates between the catchment basins and the Wady bed streams and it also assumes that the rainfall is just uniform all over the whole basin which might not always be true. The first approach lump sum the whole system unknowns, nonuniformity and spasial variability in a single parameter of calibration which might be the Curve Number (if the CN-SCS method is adopted in this regard). The second approach, gives more insight and details and the variability in the rainfall intensity and infiltration rate from the catchment basin and the Wady bed are maintained. Based on the second approach, one could estimate the infiltrated water from the Wady bed streams separated from the interception and infiltrated water from the catchment basin it self. The second approach has therefore more unknowns and thus more calibrated parameters need to be adjusted and tuned. In case of data in-availability, the coarser approach might be more relevant (like the case in Wady Degla). However, it is usually a good habit to try different approaches and compare with them.
For the purpose of model calibration, all the historical rainfall events that took place in the last 100 year at Maadi area have been investigated. Based on the recorded historic events in Maad area, it has been found that the area experienced 3 major flash flood events crash down Wady Degla; one in 1913 and two events in the same year in 1945 (Jan 1st and May 14th). Unfortunately, no significant rainfall rate at Helwan station has been found corresponding to the 1913 flashflood event therefore, this flashflood event has been disregarded. For the other two events, the recorded maximum daily rainfall was about 17mm which corresponds to the 20-year event. The 1945 event can be used to qualitatively calibrate the model based on the following: - The threshold rainfall intensity above which non-zero runoff takes place should be significantly lower than 17mm. - Since the 1945 flood event is significant, it is expected that the produced water depth at the Wady outlet should be not less than 0.5m. On the other hand and due to the running development throughout the Wady, it is currently expected that the 17mm flood storm event will produce (if it occurs) less flood event and the water depth at the outlet will be significantly less because some branches of the old Wady are not currently contributing to the main Wady. - Since no runoff flow has been recorded for the last 10 years, it is expected that the threshold rainfall intensity is very close to the corresponding rainfall depth at 10year return period.
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7.
GROUNDWATER HYDROLOGY 7.1
AQUIFER SYSTEM FROM THE REGIONAL SCALE
7.1.1 General Description The aquifer system in the study area is part of a regional system that exceeds the country's boundaries. The Egyptian side aquifer system is a multi-layered aquifer that can be divided into two main systems. The first aquifer system is the deep Nubian Aquifer System (NAS) which comprises the Paleozoic and Mesozoic continental deposits and the second upper reservoir is the more recent reservoir that is called “Post Nubian Aquifer System (PNAS or shortly the Carbonate aquifer system)” and it comprises the Tertiary Carbonate Rocks in Egypt. Between the two systems, a low permeability layers of shales and carbonates (belong to the Upper Cretaceous and the lower Tertiary) exists and forms an aquitard. The NAS system consists of mainly of sandstone continental clastic sediment and it overlies the Pre-Cambrian basement complex. The NAS strata age ranges from Cambrian to the Pre-Upper Cenomanian ages and extends over four countries (Egypt, Sudan, Libya and Chad). The PNAS system exists only in Egypt and Libya and it is believed that it is under unconfined conditions all over its domain.
The Nubian Aquifer System (NAS), in its turn, is a multi-layered system of shales and sandstones and it extends over a vast area of about 2.2 million km2 in Egypt, Libya, Sudan and Chad. The Post Nubian Aquifer System (PNAS) overlies the NAS north of 26th parallel. The PNAS is bounded by the Red Sea Mountains from the east, the Mediterranean Sea from the north, the 26th parallel demarking the limit of the deposition in the south bound and 19th Meridian in the east bound. Figure 50 presents the aerial extents of the PNAS aquifer system. The PNAS system is a fissured carbonate rocks consist of the following multi-layers (arranged from bottom to the top): - Upper Cretaceous Strata, this layer directly overlays NAS system. The outcropped area of this carbonate sediment layer covers a limited area in the northern portion of the eastern desert (about 5000 km2). The thickness of this layer reaches 500m in the northern part of the eastern desert (near the study area) and except for this zone, the upper cretaceous layer is dominated by shaly and clayey faces and it has a limited conductivity and it might be considered as globally impervious or aquiclude layer that confines the underneath NAS system. Several water points are supplied from this strata including: Bir Araiyda, Saint Anthony spring and Saint Paulo spring. - Paleogene limestone Strata, this layer generally overlays the upper cretaceous layer and its outcropped area covers about 47,000 km2 in the northern portion of the eastern desert through which a good portion of the very sparse and rare rainfall gets infiltrated. It should be mentioned here that this limestone layer is of low permeability however water could be transmitted through the fissures,
64
-
cavities and fractures that serve as water conduits. There are few water points taping from these strata. El-Dakhal spring is as an example with a daily yield of 10m3/day and very good water quality (100 ppm). However, very close to Suez Gulf region, there is a karstic formation in this strata and the water becomes brine with TDS of more than 150,000 ppm. Neogene Limestone Strata, this layer generally overlays the Paleogene limestone strata and its outcropped area covers an area in the coastal portion of the eastern desert of about 2400 km2. The occurrence of saline groundwater in the upper portion of this strata is expected as it is dominated by evaporate.
Section A-A'
Figure 50:
Regional Extent of the Unconfined PNAS System
7.1.2 Transmissivity and Hydraulic Conductivity The transmissivity of an aquifer is defined as the product of the saturated thickness of the aquifer times its hydraulic conductivity. In our study area (Wady Degla) NAS is confined system thus the transmissivity equation to be used depends on the thickness of the aquifer layer. For the NAS system, the transmissivity varies from 100m2/d to more than 10000 m2/d and the transmissivity greatly increases in the north side towards the Mediterranean Sea. For the study area, the typical NAS-transmissivity value ranges from 5000 to 6000 m2/day
The hydraulic conductivity of PNAS ranges between 6.4x10-5 m/s and 2.1x10-3 m/s. It is shown that the maximum calculated value of the transmissivity is of the order of 3000 m2/day and it takes place at the east side of Qattara depression whereas the reported lowest value is of the order of 200 m2/day and it takes place in the nearby of Farafra oasis. For our study area, the typical PNAS-transmissivity value ranges from 400 to 800 m2/day.
65
It should be mentioned that the carbonate aquifer is fractured and thus the secondary porosity plays an important role in the local groundwater flow field and in the recharge rates from Wady stream beds. Figure 51 and 52 present the contour maps of the PNAS and NAS-transmissivity respectively. Regarding the hydraulic conductivity of the low permeability layer between NAS and PNAS, it is estimated to be of the order of 1.0E-07 m/s and the vertical conductivity is estimated to be three or four order of magnitudes less than the aforementioned horizontal hydraulic conductivity.
Figure 51:
Transmissivity Map of PNAS (Source: Modified from [3])
66
Figure 52:
Transmissivity Map of NAS (Source: Modified from [3])
7.1.3 Storativity of NAS The storage coefficient reported for the confined part of NAS ranges from 2.0E-04 to 8.0E-04 s. 7.2 RECENT PEIZOMETRIC AND WATER LEVEL PATTERN 7.2.1 For NAS System Figure 53 shows the piezometric map of NAS. This map was prepared based on the measurements of 170 wells (97 wells in Egypt and the rest from the wells in the other 3 sharing countries). It is noticed that there is a steep gradient to the north east side in the potentiometric field at the south west corner of the Egyptian eastern desert which reveals a global northeastern flow direction in this area. However in the study area nearby Wady Degla, the local groundwater flow direction is directed to the north bound towards the Mediterranean Sea.
67
7.2.2 For PNAS System Figure 54 shows the potentiometric map of PNAS. This map was prepared based on the measurements of 52 wells. It worth to be mentioned that no water wells taping from PNAS has been drilled in the plateau area and in the eastern desert area where our study area is located and this is because of the high salinity of the water in this unconfined aquifer system (refer to item 7.3). Despite of the lack of peizometric field measurements, it is expected that the main direction of the regional flow in the carbonate aquifer system (PNAS) is generally driven by groundwater recharge due to deep percolation from Wady stream beds and its direction is thus directed from the highlands towards the lowlands (i.e. towards the Nile Wady) [6].
Figure 53. Piezometric surface map of NAS (modified after [3])
7.3
Figure 54. Piezometric/ water level surface map of PNAS (modified after [3])
GROUNDWATER QUALITY
For the confined NAS aquifer system, particularly in the area up to latitude 30o (just to the north of Wady Degla) the water quality changes laterally and vertically. The upper part of the confined aquifer contains freshwater with TDS
