MODELING THE IMPACTS OF WATERSHED DYNAMICS ON ARROR RIVER DISCHARGE, ELGEYO MARAKWET COUNTY, KENYA

Abstract

The challenge to manage water resources in a watershed in a sustainable and appropriate manner is growing. Water scarcity is a serious problem worldwide and thus the need to understand the watershed dynamics and their impact on discharge. This can be done effectively through integrated water resource management. In Arror River watershed, there has been a lot of degradation caused by human activities and this has led to a reduction of river flows. This study sought to model the impact of watershed dynamics on the discharge of Arror River, Elgeyo Marakwet County, Kenya. The primary sources of data included the remotely sensed data and socio-economic data. Landsat 5 Thematic Mapper (for the year 1986 January) and Landsat 7 Enhanced Thematic Mapper (for 2000 and 2012 both for the month of January) with a resolution of 30 m were used for GIS analysis. A DEM with a resolution of 90 m was used to delineate Arror watershed. The secondary data included climate, river discharge and soil data. Field surveys and questionnaires were used to collect information about the indigenous and contemporary watershed management and conservation practices and other socio- economic data. In this study GIS was integrated with WEAP together with the SWAT model to analyse the various management practices in the watershed. SWAT was used to assess the impact of land use changes on river discharge while WEAP was used to assess water demand in the watershed. The results showed that the local communities in Arror watershed have their own traditional ways of managing their water catchments with most respondents (89%) reporting prohibition of cutting of trees. They also reported some modern watershed management methods with agroforestry being the most popular (67.5%). Decision Support System based on the WEAP model as well as the SWAT model were able to predict the general trend of the catchment processes with an coefficient of efficiency (EF) of 0.85 and 0.86 as well as R-squared of 0.88 and 0.81, respectively. On land use changes, there was a reduction of 3.48% on deciduous forest and 11.82% on grassland while agricultural land increased by 14.30% in the period 1986 to 2012. The average monthly flows for 1986, 2000 and 2012 land uses were 2.04 m3/s, 2.46 m3/s and 1.94 m3/s, respectively. The variation in flow is attributed to mainly land use/cover changes. Agriculture and livestock keeping are the main economic activities in the study area. The total water allocated for agriculture, domestic and livestock in the watershed was 10,333,441m3p.a with the highest consumer being agriculture in the lower catchment at 7,154,457 m3 p.a for the reference scenario (1986-2012). The total mean demand for the same period was 10,461,123 m3 p.a and thus a mean annual unmet demand of 127,682 m3 p.a. The highest mean monthly unmet water demand was that of agriculture in the lower sub-catchment in January (90,200 m3). The minimum flow requirement scenario would yield the highest mean annual flows (85,113,000 m3 p.a) while the climate varied scenario would yield the lowest mean annual flows over the 28 years (2013-2040). The management practices that would enhance the sustainable management of the watershed include contour farming, construction of a reservoir, enforcement of minimum environmental flows maintenance in the river, agroforestry and afforestation which are recommended to be applied in Arror watershed. The findings of this study are intended to contribute towards sustainable water resource management.