WATER QUALITY MODELLING OF RIVERS IN HILLY REGION

Abstract

ABSTRACT Rivers in hilly region are generally swift fast moving, steep and varying slopes, shallow depth and narrow as compared to rivers in plain regions. They are typically characterized by the presence of water falls of small to medium height, the algal growth attached to river bed stones, and small deeper pools formed in the course of river, which affect the rate kinetics of river. Thus, in these rivers significant re-aeration is caused by frequent falls and turbulence created by bed-stones; algal growth on bed-stones causes large diurnal DO variations; pools formed in the river course act as oxidation ponds which remove significant BOD and formation of thick biological slime layer on the stones and rocks at the bed in the more polluted stretches. The widely used 1-dimensional river water quality models such as QUAL2e and STREAM do not explicitly simulate these processes with the result that these models become less useful for modelling such rivers. Application of a simple 1-D water quality model was examined for a shallow and swift hilly river (Hathli Stream, Hamirpur, HP) wherein effect of benthic and attached algal photosynthesis, reaeration due to water falls, and deoxygenation due to small pools formed in river course were considered for a realistic simulation. It was observed that these factors significantly affect model calibration parameters and thus need to be incorporated in models for such rivers.