RN-42 : Procedure for hydrological network design

Abstract

Network design enters into most aspects of hydrology. Meteorological and hydrological data characteristics of watersheds, provide the basis for all water studies and determine the major aspects of hydrological and hydraulic design of water utilisation projects. In spite of its importance , studies for determining optimum density of hydrometric network in general and stream-gauging network in particular are not extensive in many countries-including India. Some of the important aspects of hydrological network design have been reviewed.

Recommendations and suggestions have been made for types and stages of network development. The network stations are to be so located that the data collected is useful in developing relations between the hydrological factors and the significant physical parameters. A minimum plan is to be considered as a first step, as the establishment of an optimum network is a desirable but much greater undertaking. Once the minimum network is operating, one should work towards the optimum network by establishing a relatively desne network of secondary stations.,

Two basic scientific problems in network design are to determine how many data acquisition points are required and where to locate them. During recent years, most approaches to network design have seemed to fall into one of following broad categories viz. the regionalization and system analysis. Regionalization deals with the distributed rather than point values and with treated data rather than in their original form. System analysis approach is based on the optimization of some goal, subject to constraints imposed upon the system.

Some typical network design studies have also been reviewed. The recommendations for India's network made by Rao have been plotted according to Langbein's analysis of comparative areal densities of stream gauging stations as a function of population densities. It is seen that while the number of stations as per existing and modified WMO norms for immediate stage fall below the reasonable objectives and minimum requirement; while the network as per WMO norms appears to be of satisfactory level for corresponding population density.

The study for design of hydrologic network in Krishna basin is a typical example of application of physical-statistical method combined with zonal characteristics approach. However, further studies with good data base would be necessary to arrive at definite conclusions for application of this approach. The review note also includes some useful information about education and training of personnel and measurement standards adopted by Indian standards Institute and International Organization for Standardization.

Though WMO norms provide useful guidelines for general network design but it does not consider the effect of man's development activities in the river basins. Benson's study indicates the likely course of action for dealing with network design problems considering the parameters such as population, per capita income, area of land and water, relief, mean annual precipitation, surface water withdrawals, average annual growth in population, irrigated area, precipitation range areally of mean annual precipitation and number of hydroelectric plants. Appropriate methodologies would have to be developed for specific regions of the country considering climatic factors, physiographic factors, population and other indices of water resources development.