Comparing Developed Manning Coefficients for some selected soils Gidan Kwano with Exiting Values

Abstract

Collapse and failure in infrastructures in Nigeria has been a concern to the hydrologist community in Nigeria. Hence the need to determine Manning coefficient for some selected types of soil. Models that describe watershed hydrology are classified according to several criteria. One of the most significant of these classifications is based on the spatial variability of the parameters that define the flow processes Hydrologic empirical models are developed with little or no consideration to the underlying physical theory and attempt to explain the natural behavior by using simple input-output relationships. With the soil types and particle sizes of the study area determined, samples were collected from each area and placed within the experimental plots and identified. Five 22.9 m by 2 m standard runoff plots with a standard slope size of 9% were prepared and soils to be studied were collected and placed in the various runoff plots to replace the existing soils in the plots. Times of concentration for the five plots were determined using five empirical equations. The results shows that the soil samples of the study area are sandy, sandy loam, clay loam, sandy clay and loamy soils. Time of concentration ranged between 14 and 27 minutes, 49.01 and 52.14 minutes and 11.17 and 6.18 minutes for SCS, FAA and time lag equations respectively. The n values obtained ranged between 0.68 to 3.70, 7.64 to 8.87 and 0.00 to 0.37 for SCS, FAA and time lag values of time of concentration. It can be concluded that the calculated Manning and runoff coefficients for the study area which is higher than the existing one should be used in the design calculation of structures.