The Relationship between Surface Water Quality and Watershed Characteristics

Abstract

The healthy water resources are necessary and essential prerequisite for environmental protection and economic development, political, social and cultural rights of Iran. In this research, water quality parameters i.e. total dissolved solids (TDS), sodium absorption rate (SAR), electrical conductivity (EC), Na⁺, Cl^-, CO₃^2-, K⁺, Mg²⁺, Ca²⁺, pH, HCO₃^- and SO₄^2- during 2010-2011 were obtained from Iranian Water Resources Research Institute in water quality measurement stations on Mazandaran province, Iran. Then, the most important catchment characteristics (area, mean slope, mean height, base flow index, annual rainfall, land cover, and geology) were determined on water quality parameters using stepwise regression via backwards method in the 63 selected rivers. The results showed that sodium absorption rate (SAR), total dissolved solids (TDS), electrical conductivity (EC), Na⁺ and Cl^- parameters are strongly linked to geology characteristics, while K⁺, Mg²⁺ and Ca²⁺ cations is linked to rainfall and geology characteristics. pH and HCO₃^- are related to area, rainfall, land cover and geology characteristics, CO₃^2- is related to area, rainfall, rangeland area and geology characteristics and SO₄^2- is related to area, rainfall, range and bar land area and geology characteristics. Adaptive Neuro-Fuzzy Inference System (ANFIS) was used for modeling the selected catchment characteristics and water quality parameters. The ANFIS models have a high Nash-Sutcliffe model efficiency coefficient (NSE)  and low root mean squares error (RMSE) to estimate water quality parameters.