hydrology Analysis of Land Use Change and Its Impact on the Hydrology of Kakia and Esamburmbur Sub-Watersheds of Narok County, Kenya

: Narok town is one of the places in Kenya which experience catastrophic ﬂoods. Many lives have been lost and valuable property destroyed in recent years. Change in land use / land cover upstream of the town area may have contributed signiﬁcantly to the severity and frequency of ﬂooding events. Runo ﬀ , which contributes to ﬂoods in Narok town, comes from Kakia and Esamburmbur sub-catchments of Enkare Narok watershed. The objective of this study was to assess the impact of land use / land cover change on the hydrology of Kakia and Esamburmbur sub-watersheds. To detect land use / land cover change, Landsat satellite images from 1985 to 2019 were used. Using supervised classiﬁcation in Erdas Imagine 2014, land use of the study area was classiﬁed into four classes, i.e., forest, rangeland, agriculture and built-up areas. Five land use maps (1985, 1995, 2000, 2010, and 2019) were developed and used to perform land use change analysis. There was rampart conversion of forest to other land uses. Between 1985 and 2019, the forest and rangeland declined by 40.3% and 25.6% of the study area, respectively, while agriculture and built-up areas increased by 55.2% and 10.6% of the study area respectively. Analysis of soil hydrological properties indicate that the inﬁltration rate and soil hydraulic conductivity were greatest in forest than in other land use types. The basic inﬁltration rate in forest land was 89.1 cm / h while in rangeland and agricultural land, it was 7.9 cm / h and 15 cm / h respectively. At the top-soil layer, average soil hydraulic conductivity under forest was 46.3 cm / h, under rangeland, 2.6 cm / h and under agriculture, 4.9 cm / h. The low hydraulic conductivity in rangeland and agriculture was attributed to compaction by farm machinery (tractors) and livestock respectively. An interesting observation was made in rangelands where the top layer (0–20 cm) had a higher bulk density and a lower hydraulic conductivity as compared to the next deeper layer (20–40 cm). This was attributed to the combined impact of compaction and localised pressure by hooves of livestock which only have an impact on the top layer. The ﬁndings of this study show that land use has a major impact on soil hydrological properties and imply that the observed land use changes negatively a ﬀ ected the soil hydrological properties of the watershed. The decreased inﬁltration in the increasing areas of degraded land (mainly agriculture and rangeland) and increase in built-up area in Narok town are the possible causes of the increased ﬂood risk in Narok town. It is recommended that ﬂood risk management strategies in Narok town include watershed management to enhance water inﬁltration. conductivity. For example, an analysis of soil samples taken in di ﬀ erent land uses (natural forest, corn, grassland, hazelnut garden) in the Dagdami river catchment in Turkey showed that the saturated hydraulic conductivity in natural forest was 82.4 cm / h compared to that of grassland (8.4 cm / h), hazelnut garden (11.5 cm / h) and corn ﬁeld (30.0 cm / h) [8]. In another study [9], the soil hydrological properties of three land uses (degraded grass covered ﬁeld, traditional co ﬀ ee plantation and primary forest) were studied in the Talgua River watershed in Honduras and the results showed that hydraulic conductivity was lower in degraded grass compared to non-degraded lands. Under a traditional co ﬀ ee plantation and primary forest, the soils had high inﬁltration capacities and readily conducted water vertically at rates of 109 and 840 mm / h, while in land under degraded grass, the hydraulic conductivity was between 8 and 11mm / h [9].