Report Format

CE 3070-Hydraulic Design

Assignment 1: Field Identification of Hydraulic Structures and Their Hydraulic Performance

Identification of Structure Components and Important Aspects of Hydraulic Design Associated with a Village Reservoir

Madawala Ihala Wewa and Madawala Pahala Wewa, Madawala Gramaniladari Division, District Sectarian Division of Palugaswewa Anuradhapura District

Name : R.S.M. Samarasekara Index Number: 080438V Date of Sub : 20/11/2012

Contents Contents......................................................................................................................... i List of Figures ............................................................................................................. iv List of Tables................................................................................................................ v 1 Introduction .......................................................................................................... 1 1.1 Overview of the Assignment ......................................................................... 1 1.2 Objective and Specific Objectives................................................................. 1 2 General Details of the Reservoirs......................................................................... 2 2.1 Reservoir 1..................................................................................................... 2 2.2 Reservoir 2..................................................................................................... 3 3 Data Collection of Reservoir 1 ............................................................................. 4 3.1 Tank Management ......................................................................................... 4 3.2 Person responsible of issuing water .............................................................. 4 3.3 Bund Details .................................................................................................. 5 3.4 Spill Details ................................................................................................... 5 3.4.1 General Details and Status of the Spill................................................... 5 3.4.2 Condition of the Spill ............................................................................. 7 3.4.3 Downstream protection measures from erosion..................................... 7 3.4.4 Cut off walls and other aspects .............................................................. 7 3.4.5 Characteristics of Spilling ...................................................................... 7 3.5 Sluice Details ................................................................................................. 8 3.5.1 General Details and Status of Sluices .................................................... 8 3.5.2 Condition report for each sluices ........................................................... 9 3.5.3 Sluice diameter or conveyance section dimension of each sluice .......... 9 3.5.4 Inlet of each sluice.................................................................................. 9 3.5.5 Outlet of each sluice ............................................................................... 9 3.5.6 Inlet and Outlet transitions ................................................................... 10 3.5.7 Trash racks of each sluice .................................................................... 11 3.5.8 Approach path for Operating sluices.................................................... 11 3.5.9 Measuring device and Calibration in each sluice ................................. 11 3.5.10 Stilling basin of each sluice.................................................................. 11 3.5.11 Seepage cut offs of each sluice ............................................................ 11 3.6 Water Releases from each sluice ................................................................. 11 3.6.1 Water Releases from a stakeholder perspective, .................................. 11 3.6.2 Prevailing method of water control (water issues) and measurements 11 3.6.3 The waterway conditions ..................................................................... 12 3.6.4 Maintenance after the release ............................................................... 12 3.6.5 Adequacy of dead storage .................................................................... 12 3.6.6 Number of dry months ......................................................................... 12 3.7 Water Uses................................................................................................... 12 3.7.1 Direct users........................................................................................... 12 3.7.2 Main uses and Quantity of Use ............................................................ 12 i

3.7.3 Measuring method for water available in the reservoir........................ 12 3.7.4 Dead storage capacity and adequacy.................................................... 12 3.8 Stakeholder Concerns .................................................................................. 12 3.8.1 Design of the bund and associated structures....................................... 12 3.8.2 Wildlife issues ...................................................................................... 13 3.8.3 Vegetation issues .................................................................................. 13 3.8.4 Sharing of work .................................................................................... 13 4 Data Collection of Reservoir (2) ........................................................................ 14 4.1 Tank Management ....................................................................................... 14 4.2 Person responsible of issuing water ............................................................ 14 4.3 Bund Details ................................................................................................ 14 4.4 Spill Details ................................................................................................. 15 4.4.1 General Details and Status of the Spill................................................. 15 4.4.2 Condition of the Spill ........................................................................... 17 4.4.3 Downstream protection measures from erosion................................... 17 4.4.4 Cut off walls and other aspects ............................................................ 17 4.4.5 Characteristics of Spilling .................................................................... 17 4.5 Sluice Details ............................................................................................... 18 4.5.1 General Details and Status of Sluices .................................................. 18 4.5.2 Condition report for each sluices ......................................................... 19 4.5.3 Sluice diameter or conveyance section dimension of each sluice ........ 19 4.5.4 Inlet of each sluice................................................................................ 19 4.5.5 Outlet of each sluice ............................................................................. 19 4.5.6 Inlet and Outlet transitions ................................................................... 19 4.5.7 Trash racks of each sluice .................................................................... 20 4.5.8 Approach path for Operating sluices.................................................... 20 4.5.9 Measuring device and Calibration in each sluice ................................. 20 4.5.10 Stilling basin of each sluice.................................................................. 20 4.5.11 Seepage cut offs of each sluice ............................................................ 20 4.6 Water Releases from each sluice ................................................................. 20 4.6.1 Water Releases from a stakeholder perspective, .................................. 20 4.6.2 Prevailing method of water control (water issues) and measurements 21 4.6.3 The waterway conditions ..................................................................... 21 4.6.4 Maintenance after the release ............................................................... 21 4.6.5 Adequacy of dead storage .................................................................... 21 4.6.6 Number of dry months ......................................................................... 21 4.7 Water Uses................................................................................................... 21 4.7.1 Direct users........................................................................................... 21 4.7.2 Main uses and Quantity of Use ............................................................ 21 4.7.3 Measuring method for water available in the reservoir........................ 21 4.7.4 Dead storage capacity and adequacy.................................................... 21 4.8 Stakeholder Concerns .................................................................................. 21 4.8.1 Design of the bund and associated structures....................................... 21 4.8.2 Wildlife issues ...................................................................................... 22 ii

4.8.3 Vegetation issues .................................................................................. 22 4.8.4 Sharing of work .................................................................................... 22 5 Discussion .......................................................................................................... 23 5.1 Learning Outcome ....................................................................................... 23 5.2 Seepage from Bunds .................................................................................... 23 5.3 Environmental Sustainability ...................................................................... 25 5.4 Engineering Aspects of the Structures ........................................................ 27 Annex 1-Photographs Related to Reservoir 1 ............................................................ 31 Annex 1-Photographs Related to Reservoir 1 and 2 .................................................. 32 Annex 2-Photographs Related to Reservoir 2 ............................................................ 33

Note: Do not delete any section. Comment to indicate if data were not available in any section and give reasons. You may add sections at the end of each main section. Always indicate the unit of measurements. Use this guide as a template and ensure all guided elements that were given in the class room instructions have been incorporated. Provide quantifications and a description under each section.

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List of Figures Figure 2.1: Location Map of the Reservoir .................................................................. 2 Figure 2.2: Location Map of the Reservoir .................................................................. 3 Figure 3.1: Person Controlling Water of Reservoir 1 .................................................. 4 Figure 3.2: Location Sketch in the plan view of the reservoir bund ............................ 5 Figure 3.3: Sketch of the Spill and Stilling Basin ........................................................ 6 Figure 3.4: Location Sketch of the Sluices in the plan view of the reservoir bund ..... 8 Figure 3.5: Sketch of the Cross Section across the Sluice Pipe in Scour Sluice ........ 10 Figure 3.6: Sketch of the Cross Section across the Sluice Pipe in Sluice .................. 10 Figure 4.1: Person Controlling Water of Reservoir 1 ................................................ 14 Figure 4.2: Location Sketch in the plan view of the reservoir bund .......................... 15 Figure 4.3: Sketch of the Spill and Stilling Basin ...................................................... 16 Figure 4.4: Location Sketch of the Sluices in the plan view of the reservoir bund ... 18 Figure 5.1: Plan view of gout hole arrangement at bunt top level ............................. 24 Figure 5.2: Proposed Dam Section............................................................................. 25 Figure 5.3: Bad workmanship in earth channel repairing .......................................... 26

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List of Tables Table 1: Details of the Person Responsible for Water Issues ...................................... 4 Table 2: Details of the Bund of Reservoir 1................................................................. 5 Table 3: General Spill Data .......................................................................................... 7 Table 4: Characteristics of Spilling .............................................................................. 7 Table 5: General Details of the Sluices ........................................................................ 9 Table 6: Details of Sluices ........................................................................................... 9 Table 7: Dtrails of the Person Responsible for Water Issues ..................................... 14 Table 8: Details of the Bund of Reservoir 1............................................................... 14 Table 9: General Spill Data ........................................................................................ 16 Table 10: Characteristics of Spilling .......................................................................... 17 Table 11: General Details of the Sluices .................................................................... 19 Table 12: Details of the Sluices.................................................................................. 19 Table 13:Sluice - Inlet ................................................................................................ 19 Table 14: Details of the Return Periods ..................................................................... 28 Table 15: Sluice levels relative to each other and the engineering reasons for such decisions ..................................................................................................................... 29

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1 Introduction 1.1

Overvie w of the Assignment

Brief introduction to the work carried out, including the keywords Learn the key words relating to hydraulic structures with the issues related in designing processes to get good understanding of principals of water and ability to do the process design and capacity calculations meaningfully. This assignment will contribute to wide recognitio n and understanding of hydraulic structures by ensuring common procedures are followed in the development of communication strategies and design procedures and plans, including the regional technologies. Additionally, appropriate common sense development techniques and introduction to safety aspects with respect to water storage, management and conveyance are studied. Key Words: Inlet, Outlet, Inlet and Outlet transition, Stilling Basin, Cut off Wall, Tail Canal, Flux, Free Board, Return Period, Measurement Device. 1.2

Objective and Specific Objectives

Purpose of carrying out the assignment  Learn key words related to the hydraulic design subject.  Evaluate the performance of existing hydraulic structures in rural tanks.  Identify difficulties associated with design of hydraulic structures and suitable actions to overcome them.  Improve effective Communication.  Understand the principals of sustainable design and development relating to the water.  Understand the social, cultural, global and environmental responsibilities and commitment to them.  Understand the expectation of the need to undertake life- long learning and capacity to do so.  Develop the capability of undertake problems related to hydraulic design and solution.  Develop in depth competence in geotechnical and hydraulic engineering design concepts.  Improve the capability to complete works before deadline.

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2 General Details of the Reservoirs 2.1

Reservoir 1

Name: Madawala Pahala Wewa Location/Co-ordinates at the Centre of the Bund: (8°8’48’’, 80°44’60”)

Madawala Pahala Wewa

(Source: http://www.bing.com/maps/) Figure 2.1: Location Map of the Reservoir

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2.2

Reservoir 2

Name: Madawala Ihala Wewa Location/Co-ordinates at the Centre of the Bund: (8°8’35’’, 80°45’27”)

Madawala Ihala Wewa

Figure 2.2: Location Map of the Reservoir

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3 Data Collection of Reservoir 1 3.1

Tank Management

Responsible authority/agency for the water management of the tank Farmer organization of Namalpura, Galenbindunuwewa 3.2

Person responsible of issuing water

Table 1: Details of the Person Responsible for Water Issues Name of the person Mr. V. Jayasena Postal Address Namalpura, Galenbindunuwewa Contact Phone Number +94-254902527

Figure 3.1: Person Controlling Water of Reservoir 1

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3.3

Bund Details

Table 2: Details of the Bund of Reservoir 1 Bund length 600m Average bund height 5.0m Bund Slopes (Upstream) 3.1 1 Bund Slopes (Downstream) 2.2 1 Bund Top Width Seepage from Bund Cracks on Bund Is Bund top horizontal? Elevation of FSL relative to BTL Elevation of HFL relative to BTL Free Board 3.4

3.0m Prevented Not Exist Yes -1.75m -1.5m 1.5m

Spill Details

3.4.1 General Details and Status of the Spill

Scour

Figure 3.2: Location Sketch in the plan view of the reservoir bund

5

1 1.5m

Side View

Bund Top Level

A

2

30.0m Spill Level

Wing Walls A

Cross Section A-A

Reservoir

Natural Vegetation Unprotected Channel

1.0m

Concrete Wall

Plan View B Flow Direction

Unprotected Channel

30.0m

1.2m Concrete Wall

Tank Bund

B

Figure 3.3: Sketch of the Spill and Stilling Basin

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Type of Spill Length of spill Drop in elevation in spilling Length of the stilling basin

Table 3: General Spill Data Side-channel spillway 30.0m 1.0m Didn’t exist

3.4.2 Condition of the Spill  Previous spillway flows didn’t initiate a failure. A deterioration of the structure or a foundation problem or a significant external loading was not observed. Therefore existing structural damages can compromises the spillway condition.  Flows rarely exceed the spillway capacity. The flow over the spillway subjects very low flow velocities. Therefore cavitations cannot be occurred.  There exists a soil fill in the reservoir side. The stagnation pressure which is caused due to concrete cracking and spalling of joints will not be a critical case due minimum usage of concrete and most of the component of the structure was built in soil a nd rocks.  Foundation erosion is minimized due to action of concrete wall as a cutoff wall by reducing the seepage.  Hence the condition of the spill is safe. 3.4.3 Downstream protection measures from erosion  Sufficient downstream protection is not available there.  Erosion from stream banks is controlled by increasing the cross sectional area of the flow. Then the water path is passed through a deep pit/pond. When the spilling or water issuing is not in action, this causes many environmental issues such as acting as a birth place of mosquitoes. The stagnant water body is heavily subjected to eutropication (Nitrogen enrichment in water bodies). (Annex A, photo 1)  The mitigation of sedimentation problem in downstream is not engineered.

3.4.4 Cut off walls and other as pects  The embankment was constructed in Anuradhapura era and the recent major renovation is done in five decades ago. Therefore such data were not available mainly due to migration of native people from these areas. When take the durability of existing tank bund, the existence of cut off wall mechanism can be assumed.

3.4.5 Characteristics of Spilling Table 4: Characteristics of Spilling On average how many time a year does it spill? One Average flux 15cm Spill Duration 7 days Months of Spilling January 7

Last occasion the reservoir spilled December 2011 Any stakeholder comments on spilling Tank rarely spill in rainy season, Spill should renovate, Flow rises by 6 inches from top of the weir when spilling. Engineering aspect to judge the adequacy and safety of the structure Spillway occasionally experienced spilling  Adequate Large trees are grown on the tank bund, Bushes are grown on spillway, Spill tail channel is made out of earth, Not Safe Cattle cross over the spill tail channel

3.5

Sluice Details

3.5.1 General Details and Status of Sluices

Scour Sluice

Figure 3.4: Location Sketch of the Sluices in the plan view of the reservoir bund

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Table 5: General Details of the Sluices Type of sluice Scour Sluice Sluice Sluice elevations -4.0m -2.5m Gate Type and Condition Plain Gate – Plain Gate Located Downstream(Annex1,Photo2)

(0.0m – Bunt Top) 3.5.2 Condition report for each sluices  Sluice is in good condition.  Scour Sluice discharges water continuously. Condition of the sluice is bad. 3.5.3 Sluice diameter or conveyance section dimension of each sluice Scour Sluice Sluice Outlet - 30cm Outlet – Not Visible Inlet – Not Visible Inlet – Not Visible Table 6: Details of Sluices The sluice diameter is 30cm (Ask from the reservoir operator)

3.5.4 Inlet of each sluice  Score Sluice has a simple inlet. It is a submerged horizontal pipe whose diameter is 30cm, which is having a downward bend at the upstream end.  Sluice has a vertical plain gate which regulates the flow of 30mm steel pipe which is sloping to the direction of downstream at the edge of upstream tank bund.( Annex 1: Photo 3) 3.5.5 Outlet of each sluice  Sluice gate is located at its outlet of the scour sluice. There exists a downstream transition to facilitate the flow changing from trapezoidal section to a rectangular section. (Annex 1; Photo 5)  Sluice outlet directly discharge water to an earth channel section. Condition of outlet is bad. (Annex1; Photo 4)

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3.5.6 Inlet and Outlet transitions  Inlet outlet transition is simple in scour sluice. The pipe is horizontal. Following sketch shows the flow path. (Ask from a old villager)

Tank Bund Sluice Gate

30cmØ steel pipe

Inlet

Concrete Block

Dense Sand Layer around the Pipe

Figure 3.5: Sketch of the Cross Section across the Sluice Pipe in Scour Sluice  The sluice steel pipe is sloping to the upstream direction. (Ask from a old villager). This transition doesn’t take in place currently due to lack of sufficient maintenance. Sluice Channel Bed Trash Rack

Bund

Outlet

Sluice Gate

Sluice Pipe 30cmØ

Figure 3.6: Sketch of the Cross Section across the Sluice Pipe in Sluice

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3.5.7 Trash racks of each sluice  The trash rack of the scour sluice is a mesh which is covered the inlet of the sluice. The grid size of the mesh is 8cm8cm.  The trash rack of the sluice is made out of the pipes of 20mm diameter which generate 10cm10 cm grids. 3.5.8 Approach path for Ope rating sluices  The gates were located on the bund. Approach path did not exist. One of the regulators located at the outlet and other regulator is on the tank bunt. (Annex 1 ; Photo 2, Photo 3) 3.5.9 Measuring device and Calibration in each sluice  The sluice outlet is constructed with a rectangular notch. There is no any other measuring device or calibration device installed in the reservoir. 3.5.10 Stilling basin of each sluice  Both of the sluice outlets are design without a stilling basin. 3.5.11 Seepage cut offs of each sluice  The both sluices are new constructions. Hence those structures build out of concrete.  In both cases, the seepage cut-off walls should be installed. Because all outlet structures of sluices are made out of concrete and it’s very easy to provide seepage cut-offs when structures are made out of concrete and not identified unusual grass or bush growth on tank bund close to each sluices. 3.6

Wate r Releases from each sluice

3.6.1 Wate r Releases from a stakeholder perspective,  They are interested of water release from the sluices continuously after starting the cropping because a stagger system does not use in water issuing.  After a certain water level, water is not issued in dry months.  Due to improper maintenance of sluices, the water releasing is not done genuinely  The main problem in sluice is subjected to siltation due its alignment. 3.6.2 Prevailing method of water control (wate r issues) and measurements  Eutropication in stationary water.  Wrong decision making by top of the farmer organization due to lack of technical knowledge.  Infrastructure deterioration.  Risk and Vulnerability of the Water Supply System.

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3.6.3 The waterway conditions  Water regulation cannot be done properly due to poorly maintained channel system.(Annex 1; Photo 6)  90% of the channels are earth channels and they most of them are at their stable profile. 3.6.4 Maintenance after the release  No maintenance after the release 3.6.5 Adequacy of dead storage  The dead storage is not provided for this tank. But water regulators do not issue whole water in the tank. They are only issue certain amount of water. They consider that amount is sufficient to keep system alive. 3.6.6 Number of dry months  Five 3.7

Wate r Uses  To irrigation ,to protect ecological system, to consumption of farm animal , to bath

3.7.1 Direct users  200 Families 3.7.2 Main uses and Quantity of Use  Farmers, Villagers and Fishermen  500Ac.ft 3.7.3 Measuring method for water available in the reservoir  Not have a precise method. Use water marks on rocks in the tank. 3.7.4 Dead storage capacity and adequacy  Not have a dead storage. But they keep nearly 50Ac.ft as a dead storage. 3.8

Stakeholder Concerns

3.8.1 Design of the bund and associated structures Capacity adequacy, maintenance of the bund and structures, stakeholder role and division of work  The tank bunt and other related structures require a huge renovation.  Capacity is adequate but requires excavating the tank bottom. Because the tank depth is reduced due to sedimentation during last three decades.  Due to several policy issues of the government the investment on small tanks is very low. 12

 A stagger system is not adapted in water management process.  Most of the stake holders use water carefully.  There exists chena cultivation in upstream feed channels close to the tank. 3.8.2 Wildlife issues  The animal that lives in Ritigala and surrounded reserved area comes to the tank. Therefore a substantially higher crop protection is required. (Annex 1, Photo 7)  Cattle crosses the bunt is a critical issue. Because it causes damages the bund shape and degrade the soil. 3.8.3 Vegetation issues  Lotus leaves on the tank surfaces reduce the evaporation loss in storage.  Vegetation cover in the tank bunt prevents the soil degradation due to soil erosion.  The huge trees grown in tank bund cause to create large cavities in the tank bund by increasing the seepage through the bund. (Annex 1: Photo 8)  Trees and bushes grown near or on the structures cause cracks on structures due to their root complex. (Annex 2: Photo 9) 3.8.4 Sharing of work Sharing of work, water theft etc  No stagger system (In Sinhala: Bethma) associated with water management system.  People use water which was collected in low elevated area which was discharged due to leakage of the sluice. This can consider as a water theft.  Some people manufacture bricks in upstream of the tank. This is also a illegal activity.

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4 Data Collection of Reservoir (2) (Ihala Wewa and Pahala Wewa are twin tanks. Both of them were controlled by same farmer organization) 4.1

Tank Management

Responsible authority/agency for the water management of the tank Farmer organization of Namalpura, Galenbindunuwewa 4.2

Person responsible of issuing water

Table 7: Dtrails of the Person Responsible for Water Issues Name of the person Mr. V. Jayasena Postal Address Namalpura, Galenbindunuwewa Contact Phone Number +94-254902527

Photograph of the person with you

Figure 4.1: Person Controlling Water of Reservoir 1 4.3

Bund Details

Table 8: Details of the Bund of Reservoir 1 Bund length 500m Average bund height 10.0m Bund Slopes (Upstream) 3.5 1 Bund Slopes (Downstream) 2.5 1 Bund Top Width Seepage from Bund

4.0m Prevented 14

Cracks on Bund Is Bund top horizontal? Elevation of FSL relative to BTL Elevation of HFL relative to BTL Free Board 4.4

Exist Yes -3.15m -3.0m 3.0m

Spill Details

4.4.1 General Details and Status of the Spill

Natural Rock

Bund

Spill Tail Channel Spillway

Figure 4.2: Location Sketch in the plan view of the reservoir bund

15

Cross sectional vie w of spillway

2.0m M ax

6 1 1

Concrete Weir Stilling Basin 5.0m 1 3

9.0m

Natural Rock

3 1

Spill Tail Channel

6 1

Stepped Spillway 7 3

Plan Vie w

Tank Bund Wing Walls

Tank Side Weir Natural Rock Stilling Basin

Sloping Direction

Steps

Spill Tail Channel

Annex 2; Photo 1, Photo 2

Figure 4.3: Sketch of the Spill and Stilling Basin

Type of Spill Length of spill

Table 9: General Spill Data Over-fall Spillway 100.0m 16

Drop in elevation in spilling Length of the stilling basin

9.0m 5.0m

4.4.2 Condition of the Spill  Abrasion appears that given appropriate flow conditions in the presence of debris. (All of the construction materials currently being used in hydraulic structures are to some degree susceptible to erosion.) Or  High-range water-reducing admixtures (HRWRA) and condensed silica fume have not been used to develop high compressive strength concrete to overcome problems of unsatisfactory aggregate.  Even the upstream water level rises by 15cm from the spill level which ensure comparatively low flow velocity, the structure can be considered as inadequate due to use of low strength concrete which is highly subjected to the abrasion.  The mud patches on rock (Annex2, photo 4) are uniformly spread out through the rock. It implies that the cracks on the rock surface are not deep. Because if there exist no sign of flow paths. Therefore the rock should be a hard rock and seepage should be very low. Hence the structure is safe. 4.4.3 Downstream protection measures from erosion  The water path lies along a cascade made out of natural rock which is act as a lined channel. Downstream is protected from erosion. 4.4.4 Cut off walls and other as pects  There cannot see tilted trees or cracks on the bund in downstream. Therefore the downstream slope is stable. It shows that the seepage is minimized in downstream. Tank is constructed on a big rock premises. The tank bund is on a rock. It can be consider as a dam built on bed rock. There might not be a requirement of a cut off wall. 4.4.5 Characteristics of Spilling Table 10: Characteristics of Spilling On average how many time a year does it spill? One Average flux 15cm Spill Duration Two Weeks Months of Spilling January Last occasion the reservoir spilled December 2011 Any stakeholder comments on spilling The sluice was recently broken and continuously discharges water, Wearing of the concrete structure is significant. (Annex 2, photo 4), The water level rises by 15cm from top of the weir. Engineering aspect to judge the adequacy and safety of the structure Abrasion and Wear in concrete structure is significant, Inadequate 17

The structure is constructed on a huge rock, Spill tail channel lie on the rock, Mud/Water mark on the rock is uniformly spread out on the rock (Annex 2, Photo 5)(Rock is hard) 4.5

Safe

Sluice Details

4.5.1 General Details and Status of Sluices

Scour Sluice

Surge Tank

Figure 4.4: Location Sketch of the Sluices in the plan view of the reservoir bund

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Table 11: General Details of the Sluices Type of sluice Sluice elevations Gate Type and Condition

Scour Sluice -6.0m Plain Gate

Sluice -2.5m Plain Gate

(0.0m – Bunt Top) 4.5.2 Condition report for each sluices  Scour Sluice discharges water continuously. Condition is bad.  Sluice gets filled from sand. It doesn’t discharge water. Sluice is not functional. 4.5.3 Sluice diameter or conveyance section dimension of each sluice Table 12: Details of the Sluices Scour Sluice Sluice Outlet - 30cm Outlet – 30cm30cm(Square) Inlet – Not Visible Inlet – Not Visible 4.5.4 Inlet of each sluice Table 13:Sluice - Inlet Sluice Sluice Plan Vie w of concrete Front Vie w of concrete structure structure Annex 2: Photo 7 Annex 2; Photo 10

60°

30°

 Both slices seem to have same inlet and outlet shapes 4.5.5 Outlet of each sluice  Annex 2 Photo 12 shows the outlet of the scour sluice. The dimensions of the outlet of the sluice are same as the inlet of the sluice. 4.5.6 Inlet and Outlet transitions Inlet – Sub critical flow through a contraction Outlet – Flow through outlet is non uniform

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Gate

Inlet

Cylinder which contain the gate

Outlet Surge Tank

Figure 4.5: Section of the reservoir bund 4.5.7 Trash racks of each sluice 

Trash racks were not installed

4.5.8 Approach path for Ope rating sluices  No approach paths. Because the all the gates were installed in the tank bund. 4.5.9 Measuring device and Calibration in each sluice  No measuring devices were installed 4.5.10 Stilling basin of each sluice  Water directly discharges to the cement – line channels and not provides a stilling basin. 4.5.11 Seepage cut offs of each sluice  Concrete cut-off walls around a height of 1.5m were construct there 4.6

Wate r Releases from each sluice

4.6.1 Wate r Releases from a stakeholder perspective,  They are interested of water release from the sluices continuously after starting the cropping because a stagger system does not use in water issuing.  After a certain water level, water is not issued in dry months.  Due to improper maintenance of sluices, the water releasing is not done genuinely 20

4.6.2 Prevailing method of water control (wate r issues) and measurements  The attached photo shows a siphon (Annex 1 Photo 10, 11). This will ensure that the spill water will not mix with water. 4.6.3 The waterway conditions  Water regulation cannot be done properly due to poorly maintained channel system.  80% of the channels are earth channels and they most of them are at their stable profile. 4.6.4 Maintenance after the release  No maintenance after the release 4.6.5 Adequacy of dead storage  Dead storage is adequate. Even for very dry periods, this tank will not empty and much wildlife survives from this. 4.6.6 Number of dry months  Five 4.7

Wate r Uses

4.7.1 Direct users  150 Families 4.7.2 Main uses and Quantity of Use  Paddy Cultivation, Downstream Flood control, Fishing and water source for beasts of the reserved forest.  300Ac.ft 4.7.3 Measuring method for water available in the reservoir  Not have accurate or proper measuring devices in tank premises. But they use the water marks on rocks and structures to measure the water quantities of released water from the sluice. 4.7.4 Dead storage capacity and adequacy  10Ac.ft  Adequacy is enough for survival of the current system. 4.8

Stakeholder Concerns

4.8.1 Design of the bund and associated structures Capacity adequacy, maintenance of the bund and structures, stakeholder role and division of work  A siphon is provided at the outlet of the scour sluice 21

Spill Tail Channel

Channel comes from sluice

Positioning Blocks – Keep the pipe stationary

Figure 4.6: Shyphon along the spill tail channel 4.8.2 Wildlife issues  Crocodiles are living in these tanks.  Elephant walks on tank bund and surrounding causes dam ages to the tank bund.  Some wild animals fall into the “Bisokotuwa”. 4.8.3 Vegetation issues  Lotus leaves on the tank surfaces reduce the evaporation loss in storage.  Vegetation cover in the tank bunt prevents the soil degradation due to soil erosion.  The huge trees grown in tank bund cause to create large cavities in the tank bund by increasing the seepage through the bund. (Annex 1: Photo 8)  Trees and bushes grown near or on the structures cause cracks on structures due to their root complex. (Annex 2: Photo 9) 4.8.4 Sharing of work Sharing of work, water theft etc  No stagger system (In Sinhala: Bethma) associated with water management system.  People use water which was collected in low elevated area which was discharged due to leakage of the sluice. This can consider as a water theft.  Some people manufacture bricks in upstream of the tank. This is also a illegal activity.

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5 Discussion 5.1

Learning Outcome

What did you learn from this assignment? Learn the key words relating to hydraulic structures with the issues related in designing processes to get good understanding of principals of water and ability to do the process design and capacity calculations meaningfully. Key Words: Inlet, Outlet, Inlet and Outlet transition, Stilling Basin, Cut off Wall, Tail Canal, Flux, Free Board, Return Period, Measurement Device. Mention issues faced by your and how they were overcome. 1. The meanings of the key words did not clearly understood – Refer Books – Hydraulic Structure – 3rd edition, P. Novak, A.I.B. Moffat, C. Nalluri and R. Narayanan, Refer web sites – www. Wikipedia.org, published research papers etc. Ask from Research Assistance etc. 2. Communication problems occurred when asking the questions from people who managed water. Because we didn’t knew the exact meanings of English terms in Sinhala Language. – Refer Sinhala English Dictionaries, Read Sinhala articles in newspapers related to irrigation engineering, Rifer Sinhala websites related to water resource management. Past episodes of advance discussion like “Doramadalawa, ITN” 3. Places where we cannot get exact measurements of structures needed to judge the values. – The knowledge gain from already completed modules was used such as Fluid Mechanics, Hydraulic Engineering, and Irrigation Engineering etc. 4. Got problems to visit village reservoirs due to risk of elephant attacks and rainy weather. – Relatives were helped to overcome these problems in Kekirawa 5. Got limited time due to workload of other subjects. – Worked till 3.00 am to complete assignments in several nights. Make recommendations for improvements.  Give the assignment at term before start the semester. In term we have enough time to arrange visits.  If gave a chance to visit to reservoirs maintained by Department of Irrigation or Mahaweli Authority  If a guide document can provide relevant information about communication with native people will much benefiter to us. 5.2

Seepage from Bunds

If you had noticed any seepage from bund or cracks in bund, what are the reasons and remedial measures according to your engineering evaluation? Notice only in Ihala Wewa Parameters which we can use in monitoring the behaviour of the seepage and cracks Seepage and leakage quantity, location and nature can be measure. Settlement and loss of free board in embankment (magnitude and rate), internal and external deformations (magnitude, rate and location); pour water pressure and uplift (magnitude, variation) 23

Reasons for understanding of the seepage  Sand wash away from sand blanket found collect in the rubble lined toe drains. At present, it is feared that the existing pot holes would increase in number and in size, which could lead to a failure of bunt.  Water can be stored up to a far below level. ( Note: Each and every sluice also discharge continuously water)  Boggy areas were observed at eight locations on the downstream side of the embankment. Reasons which can conform the seepage  The overburden material in the bund is heterogeneous, having different layers some of which are composed of decomposed rocks.  A bore hole test – to identify the composition of soil, Core recovery test – to identify the irregularities of rocks, RQD (Rock Quality Designation) test – to identify the zones of fractures are present and the Lugeon value (A measure of rock permeability ) are important to suggest a suitable remedial action. Remedial measures  A rock grouting should be done first. Drilled two parallel lines in bund top as shown in following figure.  Clay: Cement grout is used to treat to the overburden and Cement grout is used to treat the rocky basement. Clay: Cement Grout should contain of 20:10:1 – water: clay: cement and Cement Grout should contain of 7:1 – water: cement ratio.  After doing the rock grouting, the remedial actions to the existing dam section should be taken. The main requirement is facilitate horizontal drainage and vertical drainage. The seepage should be minimized.

U/S Filled with Clay – Cement Grout Central Axis Filled with Clay – Cement Grout and Cement Grout

Grid System 1.5 m1.5 m Figure 5.1: Plan view of gout hole arrangement at bunt top level 24

D/S



Perforated PVC tubes filled inside with sand are used as the horizontal drains to dissipate pore water pressure to ensure the slope stability.

Grass – not bushes

Grout Fills

Horizontal Drains Rock Fill

Clay fills – Act as Cut off Walls

Sand Filler

Toe Drain

Figure 5.2: Proposed Dam Section 5.3

Environmental Sustainability

In your opinion what should be the dead storage for environmental sustainability for the driest months? In my opinion the dead storage what the people keep here is enough. That is 10Ac.ft for Ihala Wewa and 50Ac.ft for Pahala Wewa. Because the people who live nearby area has the knowledge to judge what is the required storage. Those people live in this area nearly 4 generations. They have a close relationship with the tank. Even they can empty the tank by scour sluice, they keep something for animal. This is a behaviour which we can appreciate. Adequacy of the structure on sustainability and safety in engineering perspective  The environmental sustainability can be adapt in dead storage concept, providing fish passes, study of ancient structures and the construction materials.  The dead storage is to survive fish, animal and plants their life in severer dry weather conditions. Therefore the existing food chains will ever last and cannot expect environmental degradation. Ecological system will not collapse.  All metallic ions will deposit at the bed of dead storage. The causes to the kidney failures will be reduced. 25

 The dead storage will keep the ground water level stable in downstream. It keeps the downstream environment stable.  The structures will not provide adequate fish paths to ahead the up steam. This is a must for last upstream ecology. Otherwise there will generate environment degradation where we cannot expect the expected economical advantage from the project.  The grown lotus leaves retard the evaporation loss. The people pluck the flowers and yams of lotus. Hence the exceeding of growing limits can be controlled.  Animal reservations in tank should keep downstream side to ensure hygiene.  The bathing places should keep in a higher elevation where the sedimentation/ mud accumulation will not occur.  Before discharge water into the agricultural purposes, the water send to a ditch called “Katta Kaduwa”. This consists of Kumbuk trees and some other native common plants. Actually this act as a wet land in water purification process. The significant eutropication is the existed problem. Otherwise this would be a very safe purification method for metallic and heavy metal ions. (Annex 1; Photo 1)  The sufficient soil erosion measures should take at the sluice outlets and the spill way outlet. Coarse gravel layer might cause significant energy loss at the place of outlet and it will help to wash out of fertile soil.  The stable profile does not keep at the earth channels and change it to rectangular section. Stable Shape Stable Shape

First Profile – Ease Construction Shape

What people do at renovation project?

Final Shape after repair

Figure 5.3: Bad workmanship in earth channel repairing  The poor farmers do not know what the expected stable shape is. They should be taught what it is. This causes extra soil erosion. (Loss of fertile soil)  The blindly use guidelines to construct structures without getting the advantages from the natural environment. Increase the height of the weir of the spillway in Ihala 26



    

5.4

Wewa. The previous spilling happens along the rock (crest profile generate along the surface of rock). The rock surface is irregular. These irregularities can be considered as installation of a projection to prevent aggregate removal due to generated vacuum between the weir and the free falling vortex. (Annex 2; Photo 2) Not provided safety rails or fences near sluices on the tank bund. The vehicles movements on the bunt are very rare. Therefore providing a safety fence is a must at least near the sluice to prevent falling to water near the sluice. The “Bisokotuwa” should cover from a net to prevent dry leaf or animal falling inside to it.(Annex 2; Photo 11) A trash rack should provide at the inlet of the siphon to prevent the blocking. (Annex 1; Photo 10) Add 2% silica fume to 930kg of cement will gives an abrasion and wearing resistance concrete. Use of hazardous and toxic materials is a negative impact. Disturbance of natural soil native vegetation, relocating inhabitants are also considering as negative impacts on the environment. Don’t allow big trees to grow on the tank bund, because the roots weaken the soil when it dies. Engineering Aspects of the Structures

What should be the design return period for the spillway and bund? Indicate reasons for your judgment. A return period also known as a recurrence interval is an estimate of the interval of time between events like a flood or a river discharge flow of a certain intensity or size. It is a statistical measurement denoting the average recurrence interval over an extended period of time, and is usually used for risk analysis (e.g. to decide whether a project should be allowed to go forward in a zone of a certain risk, or to design structures to withstand an event with a certain return period. The main depending factors of design return period, 1. The important of the structure being designed 2. The project cost 3. The level of protection it will provide 4. The damage that would result from failure of the structure The bund has an importance to last the life of both human and animals. A high level of protection is required to because a breach can endanger lives in downstream communities. If the spillway fails, the dam will be subjected to a risk or the tank will not be fully functionalized. Has a high hazard. The dam is in small scale. For average inflow downstream reservoir spills; But the downstream reservoir rarely spill. The tank bund requires minimum 150 yr. Design return period (ICE, 1996) and Spillway required minimum of 100 yr. (DOEC, revised edition 1985) Design return period. The downstream tank failure will not cause losses of human life. But it can cause lot of damages for properties. Hence 150% of 100 yr. of design period can be used to design. 27

Table 14: Details of the Return Periods Structure Dam Spillway

Madawala Ihala Wewa 150 yr. 100 yr.

Madawala Pahala Wewa 150 yr. 150% of 100 yr.

Indicate the important things that an engineer should consider when designing the sluice, bund and the turnouts  The engineer should not be a guest to the area where the structures will be constructed at his field visit. He should gather information from to perform his visual inspection and simple practical; ask past experiences of behaviour of water from the people who live nearby areas and already available data from survey department, irrigation department, and metrology department etc. Bund Designing 1. Study of available types of earth and rock fill dams and cross sections. 2. Select economically viable and safe materials for dam construction. 3. Do a geotechnical investigation. (SPT test, RQD test, Permeability test, etc.) 4. Perform a full seepage analysis with selected dam section 5. Do a slope stability analysis for downstream and up steam slopes 6. Do the environmental impact studies and suggest suitable changes to the design if impacts are existed. 7. Recommend required compaction with suitable available machineries; provide sufficient vertical and horizontal drainage etc. 8. If found leakage in testing, suitable foundation treatment and grouting methods.  The careful and correct zoning of the available materials is an important aspect of embankment design. The core width should be as great as is economically viable. The downstream shoulder should be maintain be underlain by drainage blanket, or base drain, of free – draining material. Core fill, shoulder fill drain/filter material should be necessarily done.  The selected types of structures should be tally with the proposed water management/ irrigation methods. If a structure fails at the irrigation time, many social problems can be raised which a single irrigation engineer cannot handle.  The main operational requirements for gates are failure- free performance (operational study), water tightness, rapidity of operation, minimum hoist capacity and convenience in installation and maintenance of gates should be considered select the type of gate which should install. Spillway/turnout Designing  Geotechnical and hydraulic design considerations require that to minimize the risk of damage to the dam under flood conditions the spillway and discharge channels are kept clear of the embankment. Spillways are therefore generally built on natural ground with the channel by pass sing the flank of the dam and discharging to a stilling basin clear of the downstream toe. 28

Freeboard  The provision necessary for long-term settlement within the overall minimum freeboard is determined by the height of the dam and the depth of compressible foundation at any section. It is therefore customary to construct the crest of the dam to a longitudinal camber to accommodate the predict consolidation settlement. This freeboard should be at least 1.5m Sluice  Length of transition depends on the degree of construction, approach flow condition, type of structure and permissible head loss. 1. Find out the expected discharge at the considering location. If data are not available use synthetic hydrograph theory. 2. Study the way of transition based on literate and suggest a better transition type 3. Calculate the expected width of the jump 4. Calculate the length and width of the stilting pool  United States Bureau of Reclamation (USBR) guidelines are used to design inlets and outlets. Riprap and gravel protection should provide to the adjacent to the structure in earth faced channels. The transition of sub critical  super critical should occur within the concrete lined structure. Sluice levels relative to each other and the engineering reasons for such decisions Table 15: Sluice levels relative to each other and the engineering reasons for such decisions Structure

Sluice

Relative level with respect to sluice level Ihala Pahala Wewa Wewa 0

0

Reason

A level between the maximum heights of irrigable lands from the gravity fed system and the level which can provide maximum water quantity.

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Sluice level varies between these levels

Maximum irrigable land is governs by this height Maximum water quantity can be released is govern by this height Section of the bund – Front View

Scour Sluice

-3.5m

-1.5m

Bunt Top

6.5m

3.5m

Spillway

3.5m

1.75m

Spill tail channel

-2.5m

-1.5m

To clean the reservoir when filled with mud and sand in renovations To empty the tank if a sudden draw drown may require To store water when the spill way cannot discharge completely the accumulated water at a storm or a critical flood time (Spillway Height + Freeboard) To discharge excess water to ensure the safety of the bund To ease the discharge water from command area to prevent soil salinity

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Annex 1-Photographs Related to Reservoir 1

Photo 1: Pond in spill tail channel

Photo 3: Sluice Inlet

Photo 5: Channel Section Transaction at Outlet of Sluice

Photo 2: Scour Sluice Outlet

Photo 4: Sluice Outlet

Photo 6: Poorly maintained Channel System 31

Annex 1-Photographs Related to Reservoir 1 and 2

Photo 7: Bench Mark at end of the reserved area

Photo 8: Damages caused by cattle crossing

Photo 9: Damages caused by grown bushes and plants on structures

Photo 10: Inlet of an invert siphon

Photo 11: Main Sluice outlet crossing the spill tail channel

Photo 12: Main sluice outlet

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Annex 2-Photographs Related to Reservoir 2

Photo 1: Stilling Basin

Photo 3: High Flood Water Marks on Rocks

Photo 5: Mud patches on the rock

Photo 2: Spillway

Photo 4: Abrasion in concrete due to flow of water

Photo 6: Sluice Gate 33

Photo 7: Sluice Inlet

Photo 8: Sluice Outlet

Photo 9: Mud Sluice

Photo 10: Mud Sluice - Inlet

Photo11: Surge Tank (Bisokotuwa)

Photo 12: Mud Sluice - Outlet

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