Derivation of low flow maps by transferring

General characteristics of low flow and its spatial variation are used in design of water diversion projects, hydropower، water resources studies, threshold discharge for environmental purposes, allowable sewer discharge into rivers, river ecological requirements, and water resources priority studies. Analysis of low flow with different durations and return periods and transposition of regional models are the main objectives of this paper. This research has been carried out in watersheds of Gilan province located in northern Iran with an average annual precipitation of 1100 mm.
After extracting 13 physiographic indices of the watersheds using geographic information systems (GIS), watershed area, average annual rainfall, and watershed slope were determined as the most effective parameters in step by step regression. Regional multivariable models for various low flow duration and return period were then derived. Flow accumulation map was generated using GIS and the regional models were continuously mapped in the stream networks. Moreover, the variation of low flow against distance (so called profile) was plotted for close inspection of low flow change along the streams. In this research, the technique of mapping low flow in GIS was introduced and its application to Gilan watersheds was demonstrated. The low flow maps could be effectively used in site selection of water resources projects and preparation of base hydrological drought maps.