Theme 8-14-Discharge measurement in turbulent streams of the middle mountains in Nepal.

Abstract

In mountainous areas such as the mountain ranges of the Hindu Kush – Himalayan region, the measurement of discharge is very difficult. This is due to high variability of the flow and turbulent stream conditions mainly during monsoon season. For the planning and design of water resources projects, however, reliable information on water quality with its spatial and temporal variability is necessary. The selection of the most appropriate instrument or method for discharge measurement in different flow conditions is the first step to accurate information on surface water conditions.

In the PARDYP Nepal watershed, Yarsha Khola, three techniques are applied: current meter, salt dilution and Uranin tracer. Depending on which method is used, different values of discharge are obtained at the same location. This ultimately results in different stage – discharge relationships. Inaccuracies in the stage – discharge relationships can cause major errors in the estimation of available water resources or flood discharge.

The presented paper discusses which method is the most appropriate under given condition and which values are to be taken for the development of the stage – discharge relationships. The results are derived from three years field measurement at various sites in the Yarsha Khola watershed during different flow conditions in monsoon as well as dry season.