Abstract
The calculation of loss is vital for design flood estimation models and in order to estimate continuing loss (CL), proportional loss (PL) and volumetric runoff coefficient, the surface runoff has to be separated from the total given in a stream flow hydrograph. To obtain the volume of surface runoff from the streamflow hydrograph, baseflow separation becomes necessary and in this paper a few base flow separation methods are explored and an appropriate method selected to assess to impact of baseflow on loss estimates. The process of separation requires a base flow separation coefficient and this coefficient (�) is selected from individual study catchments from 3 to 5 rainfall streamflow events of the same catchments based on sensitivity analysis. The selectedvalue of individual catchments is then applied to other rainfall streamflow events of a given catchment. It has been observed that a small degree of error in the selection ofvalue does not seem to affect the estimates of the CL, PL or runoff coefficient. Hence, the more practical base flow separation method used in this paper may be applied to other rural catchments for baseflow separation in design loss studies.
Highlights
Flood estimation is often required in hydrologic design and has important economic significance for low lying lands that are close to rivers 1,2
Rainfall-based flood estimation techniques are most commonly adopted in practice and they require a number of inputs/parameters to convert design rainfalls to design floods
Long term rainfall data were purchased from Bureau of Meteorology (BoM) and respective stream flow data were collected from DNRM
Summary
Flood estimation is often required in hydrologic design and has important economic significance for low lying lands that are close to rivers 1,2. Rainfall-based flood estimation techniques are most commonly adopted in practice and they require a number of inputs/parameters to convert design rainfalls to design floods. The simplified lumped conceptual loss models are generally used because of their simplicity and ability to approximate catchment runoff behaviour[4]. In Australia, the most commonly adopted conceptual loss model is the initial loss-continuing loss (IL-CL) model[4]. For a specific part of the catchment, the initial loss occurs prior to the commencement of surface runoff, and can be considered to be composed of the interception loss, depression storage and infiltration that occur before the soil surface saturates[3]. CL is the average rate of loss throughout the remainder of the storm
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