Runoff and Streamflow

Abstract

Rivers have served as the lifeline for mankind and continue to do so. Streamflow data are the most important hydrological data for surface water analysis. Streamflow records are primarily continuous records of flow passing through a particular section of the stream. These data are analysed to determine the magnitude and variability of surface waters. They constitute input in planning, design, and operation of surface water projects and are also used in design of bridges and culverts, flood forecasting systems, and flood plain delineation. Before describing the use of streamflow data, it is helpful to know how these are observed. 5.1. ACQUISITION AND PROCESSING OF STREAMFLOW DATA A network of stream gauging stations is established to collect data about surface water resources. The location of gauging sites depends on the purpose of data collection. If the site is needed for a specific project, the general location is in the vicinity of the project. However, if the objective is to study the general hydrology of a region, careful planning is required to identify locations so that optimum information is obtained for the resources deployed. The number of gauging sites depends on the cost of installation and operation, the value of the data, watershed size, degree of development, objective of data collection, accuracy, hydrologic characteristics, etc. Some of these factors are interrelated. For example, large watersheds involve costlier projects and more data are needed. River water level (gauge) and discharge are of immense use in water resources management. Gauge or river stage is the water level of a river at a given location and time measured with respect to some datum. A continuous observation of the river water level or stage can be made with comparative ease and economy. Discharge is the volume of flow passing through a section per unit time. Measurement of discharge in a natural channel is comparatively difficult, time consuming, expensive and requires special skills. Therefore, the discharge at a site is measured less often. Usually, the stage is measured at short intervals while discharge is measured once each day. A relation between stage and discharge at a section, termed as rating curve, is used to transform the observed stages into discharges. 193