Development of a Cell-based Model to Derive Direct Runoff Hydrographs for Ungauged Mountainous Basins

A model to derive direct runoff hydrograph for an ungauged basin using the physical properties of the basin is presented. The basin is divided into grid cells and canal elements. Overland flow is generated from each grid cell of the basin by application of continuous effective rainfall of I mm/hr to the basin, The flow generated is routed through downstream grid cells and the canal elements using the kinematic wave approach. The travel time for direct runoff from each grid cell to the basin outlet is calculated and the S-curve is derived for the basin. The S-curve is used to derive the unit hydrograph of a given duration for the basin. The model, referred as Cell-basin model was applied to the Upper Kotmale Basin in Sri Lanka and the model predictions of direct runoff hydrographs for rainfall events agreed with the observations to a reasonable accuracy. Comparison of the unit hydrographs obtained from the model and from the conventional Snyder＇s synthetic unit hydrograph using regionalized parameters assuming the basin as an ungauged basin, with the unit hydrograph derived from the observations showed that the model predicted unit hydrograph was more suitable than that obtained by Snyder＇s method for Sri Lankan up country basins. Thus, the present model is a useful tool to obtain direct runoff hydrograph for ungauged basins.

Predicting erosion and sediment yield in a mesoscale basin in the semiarid monsoon region Miyun/China

Introduction:Changes in land use and agricultural management have caused a strong increase in sediment and particulate phosphorus input into the Miyun reservoir.The simulation of the relevant runoff and sediment fluxes at the mesoscale needs adequate procedures,adapted to a semiarid monsoon climate and regional land-use pattern.Results:The modified Universal Soil Loss Equation(USLE-M)was integrated into the STOFFBILANZ model to calculate daily soil losses in the entire Miyun catchment area.The results are well within the range of monitoring data from Wischmeier plots that are located inside the investigation area.For the reference year 2009,soil erosion was estimated at an average of 952 kg ha^(-1) year^(-1).Daily based simulation of sediment input into surface waters was done in the next step,taking into account the likeliness of sediment input and sediment delivery ratio.Average sediment inputs are by 113 kg ha^(-1) year^(-1).Critical source areas are located on cropland and are particularly relevant on the former lakebed of the Miyun reservoir which has recently been used for corn cropping.Conclusions:Compared with observation data from the Bai and Chao rivers,the simulation of sediment loads showed a satisfying agreement that underlines the suitability of the selected approach to substitute recently used one-year balances based on the Universal Soil Loss Equation(USLE)approach.Conservation tillage was selected as a possible mitigation option to reduce soil erosion and sediment loads.Owing to the limited availability of spatial and monitoring data,the simulations are approximate and only a first step in contributing to an integrated river basin management that should be improved in future.