Water for people.pdf - WHO Thailand Digital Repository

C H A O P H R A Y A R I V E R B A S I N , T H A I L A N D / 3 9 3Table 16.3: Annual average runoff in the sub-basinsSub-basin Catchment area Total volume(km 2 ) (Mm 3 )Ping 35,535 9,073Wang 11,084 1,624Yom 19,516 3,684Nan 32,854 11,936Sakae Krang 5,020 1,096Pasak 15,647 2,823Tha Chin 18,105 2,449Chao Phraya main stream 21,521 4,435Total 159,283 37,120Runoff is fairly constant all over the sub-basins; the Wang and Tha Chin sub-basins show ahigher runoff.of 26,400 km 2 . The installed hydroelectricity generation capacityis 713 megawatts (MW). The dam was completed in 1963, andfilled for the first time in 1970. Sirikit dam on the Nan Riverwas completed in 1972 and has a live storage capacity of 6 bm 3compared to the average annual inflow of 5.9 bm 3 . The installedhydroelectricity generation capacity is 500 MW. Several otherlarge dams (Kiew Lom, Mae Ngat, Mae Kuang, Mae Chang, ThapSalao and Kra Sieo) have also been built during the last twentyyears to increase the total surface water storage in the basin,while another, the Pasak dam, was commissioned in 2000. Table16.4 presents some information on selected dams in the basin.BarragesA number of barrages have been constructed in the Lower ChaoPhraya basin to control and divert the water in the canal systemsthat provide irrigation water to some 1 million hectares in thisarea. The most important barrages in the delta area are the Rama VIbarrage, completed in 1924, and the Chao Phraya (Chainat)diversion dam on the Chao Phraya River, built in 1957. Althoughthe Rama IV barrage was constructed about seventy-five yearsago, it still maintains its structure and remains operational. Thesebarrages divert water to a complex system of interconnectingcanals serving the Lower Chao Phraya basin irrigation system.Barrages have also been constructed above the Chao Phrayadiversion dam. The Naresuan dam across Nan River at Phitsanulokwas completed in 1985 and diverts water to the whole area of thePhitsanulok Phase I Project. The water released from the Sirikitdam meets the requirements of the Phitsanulok Irrigation Projectas well as part of the demand for the Chao Phraya Delta area.GroundwaterAquifer distributionHydrogeologically, the Chao Phraya River basin is comprised of sevengroundwater sub-basins: Chiangmai-Lampoon basin, Lampang basin,Payao basin, Prae basin, Nan basin, Upper Chao Phraya basin andLower Chao Phraya basin. Within these groundwater sub-basins,water is held in either confined or unconfined aquifers. Eightseparate confined aquifers are located in the Upper Tertiary toQuaternary strata of the Bangkok area. The natural groundwaterwithin this succession of aquifers is highly confined, creating artesianconditions in each. Ease of exploitation, as well as the high chemicalquality, are the main reasons for the original development of thissource. Groundwater storage and renewable resources have beenestimated for each groundwater sub-basin, as shown in table 16.5.Recharge, flow and dischargeThere are few existing estimates available of groundwaterrecharge on a regional basis. In an artesian aquifer, as thatbeneath Bangkok, storage depletion is seen through a decline inpiezometric pressure and a reduction in the area in whichTable 16.4: Characteristics of major reservoirsMaximum retention Normal retention Minimum retention Effective storageReservoir name Sub-basin (Mm 3 ) (Mm 3 ) (Mm 3 ) (Mm 3 )Bhumiphol Ping 13,456 13,462 3,800 9,662Sirikit Nan 10,640 9,510 2,850 6,660Kiew Lom Wang 112 112 4 108Mae Ngat Ping 325 265 10 255Mae Kuang Ping 263 263 14 249Mae Chang Wang 108 NA NA NAThap Salao Sakae Krang 198 160 8 152Kra Sieo Tha Chin 363 240 40 201Pasak Pasak 960 NA NA 785The two largest dams of the Chao Phraya River basin are Bumiphol and Sirikit; together, they control the runoff from 22 percent of the entire basin.