Micro-level Assessment of CN Based Runoff in an ungauged Subwatershed of Tamilnadu, India

Abstract

Abstract-CN method is a globally accepted, practical method to estimate the direct runoff depending on land use/land cover (LULC), soil type and its antecedent moisture condition (AMC). In the present study, micro-watersheds level runoff from the upper Manimuktha sub-watershed (4C1A2e) of Tamilnadu, India, has been assessed. IRS 1C LISS-III satellite image in 2012 was used to obtain LULC information. Hydrologic Soil Groups' (HSG) map was prepared from the soil map of the study area. The daily rainfall data were collected from Gomukhi dam and Manimuktha dam raingauge stations for 6 water years (2011)(2012)(2013)(2014)(2015)(2016)(2017) and converted to weighted spatial distributed rainfall by Thiessen polygon method and used to calculate the daily, monthly and annual runoff. CN map of the micro-watersheds was made by integrating HSG and LULC maps by using ArcGIS 10.5 software. The weighted CN for AMC II condition of the sub-watershed was 81.72 and of the microwatersheds it ranged from 59 to 89. The average annual minimum and maximum runoff were 64.28mm (in 2016-2017) and 573.96 mm (in 2011-2012). The high runoff potential was occurred in 25 micro-watersheds of area 103.483 km 2 and very high runoff of 37.986 km 2 in 6 micro-watersheds. This study will be useful to estimate runoff from an ungauged watershed having same characteristic.