Improved Continuing Losses Estimation Using Initial Loss-Continuing Loss Model for Medium Sized Rural Catchments

Mahbub Ilahee,Monzur Alam Imtea

doi:10.3844/ajeassp.2009.796.803

Abstract

Problem statement: The rainfall based design flood estimation techniqu es are commonly adopted in hydrological design and require a number of inputs including information on soil loss characteristics. Approach: A conceptual loss model known as the 'Initial Loss- Continuing Loss (IL- CL) model' is widely used in Australia. Results: The Initial Loss (IL) occurs at the beginning of th e rainfall event, prior to the commencement of surfac e runoff and the Continuing Loss (CL) is the average rate of loss throughout the remainder of th e storm. The currently recommended design loss values depicted in Australian Rainfall and Runoff Vol. 1 for Queensland (Australia) has some basic limitations. This study investigated how more accur ate CL values can be estimated and derived for medium sized tropical Queensland catchments using long term rainfall and streamflow data. Accuracy in CL estimation has got significant implications i n the estimation of design floods. Conclusion/Recommendations: The results showed that CL value is not fixed and constant through out the duration of the storm but the CL value deca ys with the duration of the storm.

Highlights

In design flood estimation, simplified lumped conceptual loss models are commonly used because of their simplicity and ability to approximate catchment runoff behavior
The rates of continuing loss are constant as recommended in ARR[4], in reality the value could be decreasing with the time depending upon the soil cover and duration of the storm
It is found that continuing loss value decreases with the increase of the duration of the rainfall event i.e., Continuing Losses (CL) value is not a fixed single value for a catchment as recommended in ARR[4] but it decays with the increase in the duration of the storm

Summary

Introduction

In design flood estimation, simplified lumped conceptual loss models are commonly used because of their simplicity and ability to approximate catchment runoff behavior. The common loss factors include rainfall intercepted by vegetation (interception loss), infiltration into the soil (infiltration), retention on the surface (depression storage), evaporation and loss through the streambed and banks. Many loss models do not account for the interception, depression storage and evaporation losses separately Instead, such losses are considered as infiltration into the soil. The selection of catchments was done based on the catchment size, regulation, record lengths of rainfall and streamflow data. The loss (IL-CL) model which was used in this research is only suitable for small to medium size catchments and not suitable to compute the loss values for the larger catchments. Australian Rainfall and Runoff[4] suggests the catchment area with an upper limit of 1000 km can be considered as a small to medium sized catchments, which was taken as a guide to selecting the study catchments. The gauging authority was consulted to know about any recent changes of regulation and land use in the selected catchments

Objectives

Discussion

Conclusion