Abstract:
The Mau forest complex has experienced forest destruction (clearing, felling and burning) to make room for cultivation from as early as 1970s. This has had a disastrous effect on forest cover. The forest functions in the watershed have been affected with the formerly perennial rivers such as River Njoro, which drains the catchment into Lake Nakuru becoming seasonal. The changing land use has resulted into reduced water retention capacity and increased soil erosion in the catchment. Consequently very large peaks and low flows with frequent drying up in the lower reaches are common in River Njoro. Due to increased erosion, the river deposits a lot of sediments into Lake Nakuru. These events stimulated this study that assessed infiltration rates, surface rimofi and soil erosion imder selected land use practices. The study also investigated the effect of rainfall intensity on soil erosion and surface rtmoff on different land use practices. Field rainfall simulation at different rainfall intensities was used to examine infiltration, surface runoff and soil loss on natural forest, agricultural and grazing lands in this catchment. Runoff plots were randomly established in each of the land use areas and runoff volume collected from the simulated storm for laboratory analysis. Water-sediment mixture from runoff was weighed for each sample, oven dried and the dry weight of the sample determined. It was a two—factorial experiment Where the interaction between land use and rainfall intensity treatment was investigated. A statistical evaluation ANOVA, using SAS prograrmne was used to analyse the data. Analysis of the soil was carried out to establish the corresponding soil properties for different land use practices. The study found that there was a significant difference in the mean runoff rate and soil lost from the three land use practices. Soil loss increased as rainfall intensity increased from 30 to 80 rnm/hr in the order of forest (0.0352 tons/ha), grazing (0.352 tons/ha) and agricultural land (1.45 tons/ha) which registered the highest loss. However, the highest mean runoff rate was recorded from grazing (26.46mm/hr) area followed by agricultural (2l.Olmm/hr) while forested area recorded the least runoff rate of 8.22mm/hr in all treatments. These results are useful in prioritising interventions for land and water management.
