TN-35 : Instrumentation and measuring techniques for flow measurements in mountainous area

Abstract

Flow measurements in mountainous areas are comparatively difficult and need a special attention. Stream flow is the combined result of all the climatological and geographical factors that operate in the drainage basin. Variations of these conditions in India are very wide in the range pertaining to East to West or south to North. A general feature of Indian mountain streams is the high velocity of flow. These are often deep-gorges or shallow channels with an uneven bed; carry stones, pebbles and high sediment load; have transverse, rocky/unstable slopes, high density of confluencing flow and uneven water surface or ice cover conditions in winter. Consequently stations in arid or forested zones require to be designed to measure flows from zero to major floods whereas, glacier-fed stream requires to be designed for pulsating, perennial and ice covered flows to flash floods.

Flow measuring equipments and methods applicable for mountainous stream have been indicated and discussed in this report. Review presents the scope, the limitations with relevant recommendations in adopting velocity-area, dilution gauging, control structures, gauge measurement, slope-area, and electromagnetic methods and their instrumentation based on local condition, accuracy required and maintenance possible in remote areas. The application of telemetering system in remote and application of unconventional , specially designed and portable gauges for flow measurement during expeditions are highlighted.

Part of the table prepared by WMO (TN-337) on the instruments of proven reliability and appropriate to this report are listed in Appendix II. For measurement of open channel flow, International and Indian Standards are available with reference to instruments and techniques only, and listed in Appendix I. It is required to standardize the methods of observation and instrumentation for flow measurement in Indian mountainous areas, based on climate and local conditions which are yet in the process of development in the world.