Design of On-Farm Hydraulic Structures forRegulating Road Drainage

摘要

In semi arid areas of Kenya, the highest concentrations of runoff water flow is fromroad drainage. This runoff is generated by the excessively intense storms of short duration that are common in these areas. Currently, the hydraulic and storage used for managing roaddrainage in Kenya are either inadequately designed or non-existent. Rarely have check damsbeen used to regulate road drainage. Road culverts have been constructed without provisionsfor stone aprons to dissipate the energy of runoff water. Hence undercutting and scouringdownstream of culverts has often resulted in gully erosion. In this study, attempts have beenmade to design effective hydraulic structures for regulating road drainage in Mwala, Machakos,Kenya. The hydraulic structures considered included: conveyance systems (trapezoidal andrectangular open channels); energy dissipating structures (stilling pool, sedimentation basin andstone apron). Besides, water flow measurement devices (v-notch weir and horizontal water levelrecorder) were included in the design. The design runoff discharge rate of 0.375 m3/s wasestimated using Cook' s Method and was based on a return period of 10 years. The designedhydraulic structures were found to be effective in regulating and dissipating the energy of runoffwater and discharging into a constructed micro-dam of 200-300m3 capacity. The V-notch weir(90 0) installed was effective in measuring low to medium runoff discharges expected in the area.