In the study, raingauge network design has been developed for the Pagladiya basin of Brahmaputra river in Nalbari, Assam and Bhutan. Precipitation is the most basic data required for any water resources study and the estimation of the number & location of raingauge stations that provide adequate information regarding rainfall falling over the catchment is referred to as network design. A raingauge network is intended to serve general as well as specific purposes such as water supply, hydropower generation, flood forecasting, irrigation and flood control.
A wide spatial variation of rainfall is observed in the catchment, whose annual rainfall is over 2300 mm. The rainfall occurs mostly during March to October. During March and April, the rainfall is sporadic, but steady and heavy to very heavy during May to October.
The rainfall data of ten existing raingauge stations in and around the study area has been analyzed using various methods that take into account the location of raingauges, type of basin, climate and precipitation characteristics from the existing raingauge stations.
Apart from BIS recommendations, Cv method, Key Station method, Spatial Correlation method and Entropy method have been used. The various methods suggest that the rainfall in the basin is not sampled well. All methods used in the study other than the Cv method, indicate that a maximum of eight stations are adequate to represent the rainfall in the plain area of the basin. No method other than BIS method says anything about the number of stations in the hilly part of the basin, which is mostly in the Bhutan territory. It recommends a total of four stations in the hilly portion.
Therefore, it may be inferred from the study that a total of twelve stations are required in the basin, four in the hilly portion and another eight in the plains. The Entropy method shows very high concentration of information in the north-central part of the basin, and indicates that discontinuation of two stations will not affect the adequacy of the network.
The study indicates that additional stations are required in certain parts of the basin while in other parts some redundant stations have been identified. For adequate and economical network design, discontinuation of two existing stations and installation of additional four stations have been proposed in the catchment with their possible locations.
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