Ranking the Suitability of Subwatersheds for Ponding-Based Methods of Managed Aquifer Recharge in Lower Yom River Basin, Thailand *
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Kriengsak Srisuk , Sumrit Chusanatus , Sitisak Munyou , Laa Archwichai , *
Kewaree Pholkern and Penlada Boonsongka *
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Groundwater Research Center, Faculty of Technology, Khon Kaen University, Khon Kaen,
Thailand. (
[email protected]) **
Department of Groundwater Resources, Ministry of Natural Resources and Environment,
Thailand. (
[email protected])
Abstract 2
The study area is located in the Lower Yom River Basin embracing an area of about 970 km in the lower part of northern Thailand which is underlain by sequences of unconsolidated materials of alluvium and alluvial fans of the Yom and Nan River floodplains. Groundwater has been heavily exploited from the shallow gravel, sand and silt aquifer. Drastically declining water levels, ranging from 7 to 10 meters, has been noticeable within the past decade. Therefore the Department of Groundwater Resource, Thailand considers that artificial recharge of surface water may be useful for recovering the static water levels within the most hydrogeologically suitable areas. The objectives of the paper is to identify and classify existing subwatershed in the Lower Yom river basin and select the most appropriate areas for a pilotscale testing taking experiment of managed aquifer recharge (MAR) into account the hydrogeological characteristics as well as non-hydrogeological factors using surface ponding methods. Subwatersheds were characterized based on hydrogeological mapping at a scale of 1:50,000. Hydrogeological parameters such as thickness of surficial clay, depth to first aquifer, aquifer thickness, density of existing pumping wells etc, moreover, non-hydrogeological factors such as the distance to available source water for recharge, access to power supply, land use, accessibility and availability, were considered for ponding recharge site selection criteria. Boolean Logic and Fuzzy Logic were used for delineating the subwatershed. There are 19 subwatersheds in Lanba watershed. Detailed hydrogeological investigations were conducted in the ten most prospective subwatersheds. Of these, the Ban Nong Na 3 sub-basin covering an area of about 500 hectares is one of the most appropriated sites for the MAR pilot construction and testing. KEYWORDS: Subwatershed, Managed Aquifer Recharge, surface ponding, Hydrogeological factors, Lower Yom River Basin
INTRODUCTION Extensive use of shallow groundwater for rice growing in the Lower Northern River Basin of Thailand has caused groundwater levels to decline from 1-2 m below ground surface in previous decades to 7-10 m (DGR, 2009) at the present time. Effective management of aquifer recharge is becoming and increasingly important aspect of water resource management strategies. Artificial recharge is an effective technique for the restoration and augmentation of groundwater resources. Ponding systems may be one of the simplest and cheapest methods of the artificial recharge, and is proposed to be applied to raise the groundwater levels within this area. The objective of this study is to rank the suitability of subwaterseds in the Lower Yom Basin for selection of sites and conducting a pilot-scale testing based on hydrogeological and non hydrogeological data. The study area is located in the lower part of northern Yom River Basin in 2 Thailand embracing an area of about 970 km in Bangrakham districts, Pitsanulok Province, and Samngam and Vachira Baramee districts, Pichit Provinces (Figure 1). Groundwater-based irrigation of rice paddy is a dominant land use for the largely agrarian economy in the region. Paddy field occupies more than 70% of the area (LDD, 2000) as shown in Figure 2. This area has topographic elevations vary
from 54 to 34 m above mean sea level. The Lower Yom River Basin consists of 13 subwatersheds o (Figure 1) and has a tropical monsoon climate with an annual average temperature about 28 C, annual rainfall of about 1,200 mm and annual evaporation of about 1,350 mm (Meteorological Department, 2009). The Yom River is the main river which flows from north to the south. The Lower Yom River Basin is underlain by alluvial fan, floodplain deposits, and channel and natural levee deposits. Alluvial fan deposits consist of gravel, sand, silt and clay. Floodplain deposits consist mainly of clay and silt. Channel and Natural levee deposits are composed of sand, silt and clay (Figure 3).
Figure 1.Watersheds in the study area
Figure 2. land use and existing pumping wells in the study area
Figure 3. Hydrogeological map and hydrogeological cross sections
METHODOLOGY Two main groups of hydrogeological and non-hydrogeological parameters were used as the criteria for analyses the appropriated areas. The hydrogeological parameters are thickness of surficial clay, depth to the first aquifer, aquifer thickness, density of existing pumping wells (irrigation wells). Whereas the nonhydrogeological parameters are distance to available water source, access to power supply, land accessibility and availability. These sets of information were prepared from several sources of information as well as from field investigation during the study period. The derivative maps derived from this information were produced and analyzed by overlaying technique and scoring, weighting, classifying by the Boolean and Fuzzy logic. The Boolean logic consists of AND and OR operators. Based on the set theory, the AND operator yields the logical intersection of the two data set, and the OR operator obtains the logical union of the two data sets. In classical set theory, the membership of a set must defined 1 or 0. Membership of the Fuzzy set, however, is expressed on continuous scale from 1 (full membership) to 0 (full non-membership). In contrast to Boolean logic, no certainty exists in fuzzy logic. Therefore, no unit area is definitely satisfactory or unsatisfactory for artificial recharge (Ghayoumian and Mohseni Saravi, 2007). Selection of appropriate areas is divided into three steps, namely, 1) selecting the appropriate watershed from hydrogeological characteristics which are depth to the aquifer and agricultural well density. Depth to the aquifer was interpreted from existing groundwater well logs, piezometer wells and hand auger bored logs. The agricultural well density was calculated from the ArcGIS 9.3 software. The depth to the aquifer and agricultural well density was integrated in GIS by Boolean logic acceptable ranges as shown in Table 1. 2) Watershed area were divided into subwatersheds and selected subwatersheds were preliminary chosen based on Boolean logic. The result of the initial interpretation was used to integrate with the second group of the parameters as tabulated in Table 2. 3) Reanalyzing the initial results with the new sets of parameters, such as aquifer thickness, access to power supply and land availability and were interpreted by Fuzzy logic. Classification, membership of the Fuzzy set and weight of parameters were assigned for each parameter based on the field evidences and previous works (Table 3).
Table 1. Acceptable ranges of selecting the appropriate watershed Parameter
Acceptable ranges
Depth to aquifer (m)
0-5 2
Agricultural wells density (wells/m )
More than 15
Table 2. Acceptable ranges for preliminary selection of the appropriate subwatershed Parameter
Acceptable ranges
Depth to aquifer (m)
Less than 3 2
Agricultural wells density (wells/m )
More than 5
Distance to available source water (m)
Less than 1500
Land accessibility
Easy
Table 3. Criteria selection of the appropriate subwatershed in Fuzzy logic Parameter
Classes
membership
weight
Aquifer thickness
More than 15
1
3
10-15
0.75
5-10
0.25
Less than 1
1
1-2
0.75
2-3
0.25
More than 20
1
20-10
0.6
10-5
0.2
Distance to available source
Less than 200
1
water (m)
200-500
0.7
500-1000
0.4
1000-1500
0.2
Less than 500
1
500-1000
0.5
1000-1500
0.2
Pubic land
1
Land field
0.8
Paddy field
0.6
Depth to aquifer (m)
Agricultural wells density 2
(wells/m )
Access to power supply
Land availability
3
2
2
1
1
RESULTS Lanba watershed is one of the most suitable watersheds from 13 watersheds exiting in the Lower Yom River Basin for MAR as shown in Figure 4. The Lanba watershed consists of 19 subwatersheds as shown in Figure 5. Eventually, there are only 10 subwatersheds, namely, BK-1, BK-2, DKK1, NM-2, NN-1, NN-2, NN-3, PK1, SS-2, TC1 and TC2 that were selected for the detailed study. NN3 subwatershed (Nong Na 3) is one of the most appropriate sites for the MAR Pilot test site. Nong Na 3 subwatershed (Figure 6) is located in Nong Na Village Bangrakham district, Pitsanulok Province covers an area of about 500 hectares. Paddy field and sugar cane plots are the main land uses and occupy more than 85% of the area. Rainwater and existing creeks within the Nong Na area flows through the area and discharging to the Lanba stream located in the northern region. In this area, there are about 90 agricultural wells that have been pumping ground water from the shallow aquifer (10 to 15 meters below the ground surface). The high well density zone is located in the northern region near the Lanba stream. Therefore, the detailed hydrogeological investigation is conducted within Nong Na 3 subwatershed in order to locate the final construction site for the MAR pilot project.
Figure 5. Subwatershed in Lanba watershed
Figure 4. Lanba watershed appropriate watershed for MAR
Figure 6. Nong Na 3 subwatershed
CONCLUSIONS AND RECOMMENDATIONS Diverse and complex arrays of criteria for determining the suitability of areas for MAR can be generated during the study. However, field investigation with the GIS analyses is a useful method in delineating the detailed study areas for MAR using ponding recharge system. Moreover, this simple technique described here can also be adapted and employed to determine the suitability of other MAR techniques, such as trenching, roof-runoff rainwater harvesting, recharge weir, and Aquifer Storage and Recovery (ASR) for the future studies.
ACKNOWLEDGEMENTS We would like to thank the Department of Groundwater Resources, Ministry of Natural Resources and Environment, Thailand for providing financial support to the project.
REFERENCES Department of Groundwater Resources (DGR). 2009. Pilot Study and Experiment on Managed Aquifer Recharge Using Ponding System in the Lower North Region River Basin, Pitsanulok, Sukhothai, and Pichit Provinces. Progress Report No. II. Groundwater Research Center, Khon Kaen University, Thailand. Department of Meteorological. 2009. Weather information of Pitsanulok, Sukhothai, and Pichit Provinces (1995-2009). Bangkok, Thailand. Ghayoumian, J., Mohseni Saravi, M., Feiznia, S., Nouri, B. and Malekian, A. 2007. Application of GIS techniques to determine areas most suitable for artificial groundwater recharge in a coastal aquifer in southern Iran. Asian Earth Sciences, Vol. 30 pp 364–374 Land Development Department (LDD). 2000. Soil Series Map, scale 1:50,000 (report on land use by province). Bangkok, Thailand.
