e - poz 2 - Central Institute of Brackishwater Aquaculture

of this century. The current lwei of depth in the sourhem sector of the lakeob~ed under the present study was 2.2m, a further depletion of 0.51.3m in aspan of 20 years approximating to 86000 ham.Table 2. Reduction in depth range in different Mom of Vcmbarud lakeover a period of 50 yeanSectors-Depth-range (In mrs)South oi Thanneermukkom bund5QYmulU89 3-3.5.Brtwwn Thannerrmukkom bund and Vaikom 8-9 3 -4Betwe-n Valkom and South Paravmr 7-9 4-5B~rwwn 50uth paravmr and Armr 5-6 34Between Arcmr and south 01 Well~ngton Island 7-8 7-8Bolghdn~ to Chrra~ 3-4.5 2-2.5tl11~rd1 10 Mundmbarn 3-6 2.5-4RIVER DISCHARGE IN TO THE LAKEThe rlvers, which d~rectly drain into the Vembanad wetland system are Chalakudy(1 700 km', 130 km), Periyar (5400 km', 244 km) and Muvattupuzha (1 550 km',12 1 km), In the northen sector, and Meenachal(1250 km', 78 km), Manimala (850km', 90 km), Pampa (2250 km', 176 km) and Achancoil(1500 km', 128 km) In thesouthern sector (Fig.1). The basins together cover an area of about 16200 km' outof which 22 % lies in the lowland, 23 % in the midland and the remaining 55 %In the highland. The rivers flow down the highlands over steep slopes of almost60mkm and more, and traverse the~r midland stretches with much flatter slopes ofabut 1 d m.The rivers are estimated to bring in a total of 10074 million m' of water to the lake(Table3). Of this, 66.54 % are brought in during the three months of the southwest monsoon and 11.67 % during the north east monsoon in October. Only 22% of the discharge are spread among the rest 8 months. Practically there ts noseaward flow of river water during t k months.