Morphometric analysis is important in any hydrological investigation and it is inevitable in development and management of drainage basin. The present study is an attempt to evaluate and compare various morphometric parameters and prioritization of micro-watersheds based on water holding capacity of Kokkayar sub-watershed, a typical highland sub-watershed of Manimala river basin. Morphometric analysis and prioritization of micro-watersheds have been achieved through measurement of linear, aerial and relief aspects of basins by using remote sensing and GIS techniques, and it necessitates preparation of a detailed drainage map. For prioritization, 9 micro-watersheds are delineated and morphometric parameters such as Rb, Dd, Fs,T, Lof and C are calculated separately and prioritization has been done by using the Raster calculator option of Spatial analyst. The analysis reveals that the stream order varies from 1 to 4 and the total number of stream segments of all orders counted as 200. Lsm varies from 0.50 to 7.55. Higher value of mean Rb (4.17) (linear parameters), higher values of Bh (0.08), Rh (0.07) and Rn (3.02) (relief parameters), high values of Dd (3.2), Fs (6.3), T (5.63) and low values of Lof (0.16) and C (0.31) (aerial parameters) all together reveal that the sub-watershed has a complex structure, mountainous relief, high runoff and low infiltration. The maximum area is covered by high prioritized zones (12.72 km2) followed by very high (10.63km2) while very low zone is only 9.37 km2.

The present study encompasses an assessment of annual and long term variations in groundwater level of Peruvanthanam and Valiyathodu sub-watersheds and its correlation with rainfall occurrence. The seasonal variations in phreatic surfaces of both sub-watersheds reveal that unlike Peruvanthanam, Valiyathodu sub-watershed shows maximum fluctuations in groundwater level during post monsoon season. Average rainfall in Peruvanthanam sub-watershed during this period was 3832.28 mm and the average water levels in the observation wells CGWBp1 and CGWBp2 were 4.86m and 2.62m respectively. In 2007 when there was an increase of 1199.72 mm rainfall from the average. Well no. CGWBp1 shows a decrease in water level from 4.36 to 4.10m ie, 0.76 m (15.64%). The corresponding decrease in value observed in groundwater level of well no CGWBp2 was from 2.62m to 2.20m ie, 16.03%. When both the well data are compared, greater variations are observed, in well no.CGWBp2 during increase in rainfall. This is a reflection of the greater porosity and permeability of the ground material in an around the well. Similarly in 2000, there was a decrease of 1296.78mm in rainfall from the average. In well no CGWBp1 there was an increase in depth from 4.86m to 5.59m ie, 0.71m (14.61%). The corresponding value for well no CGWBp2 was from the average value of 2.62m to 2.95m ie, 0.33m (12.60%). Average rainfall of Valiyathodu sub-watershed was 4099.82mm and the average water level in CGWBv1 and CGWBv2 are 9.12m and 5.64m respectively. In 2005 when there was an increase of 1031.68mm rainfall from the average well no. CGWBv1 shows a decrease in value from 9.12 to 7.82 (14.25%). The corresponding variations observed in well no. CGWBv2 was from 5.64m to 5.16m (8.51%). In 2002 there was a decrease in rainfall to 3089.00mm from the average value of 4099.82mm. The variation in groundwater level observed in well no. CGWBv1 in accordance with this is from 9.12m to 10.01m ie, 0.89m (9.76%). The corresponding variations observed in well no. CGWBv2 is from 5.64m to 5.98m ie, 0.34m (6.03%). When both well data are compared, greater variations are observed in well no CGWBv1 during both increase and decrease in rainfall. This shows that sub surface phreatic aquifer material in around well no. CGWBv1 has more permeability compared to CGWBv2.