Development of an Integrated Mathematical Model on Water Quantity and Quality and its Application to the Weihe Basin

The Yellow River basin is the largest one in North West and North China, covering 752 thousand km(2) and accounting for 8% of the area of China. The basin is characterized by arid and semi-and climate, the Loess Plateau, and industrially developing and highly cultivated area. It has been suffering from water shortage and heavy sediment transport. Appropriate allocation of water resources is of importance in the basin for development and sustainability. Appropriate allocation of water resources would bring better ecosystem and higher sustainability with wise water use, efficient water reuse, and discharge of wastewater after appropriate treatment. Allocation of water resources to the sectors; agriculture, industry, daily lives, and ecosystem, is a matter of policy and economy. Water use with high efficiency is of technology and of social systems, and water reuse is of technology, health risk, and economy. In order to reach more appropriate allocation, what have to be done are to construct an integrated modeling on water quality mid quantity in an objective area and to simulate future figures in the area. Since polluted water, even if it is fresh water, does not become water resources, water quality is of necessity for water reuse. In this study, an integrated water quantity and quality model is developed to apply to the Weilie basin, the major tributary of the Yellow River, as an objective area. The model consists of two sub-models, a water circulation sub-model and a water quality sub model, which are based on the GBHM2 model (geomorphology-based hydrological model 2) and the Streeter-Phelps model with the 1-D diffusion term, respectively. In order to make water reuse with high efficiency possible, discharging points are also identified. The pattern of precipitation, surface flow rates, the groundwater flow level, and evapotranspiration rates are taken into consideration in it. The amount of evapotranspinition is estimated with the Penman-Monteith method and with hourly changes of temperature and precipitation. Parameterization and determination of boundary and initial conditions are done by use of GIS data, satellite images, observation data on site, and statistical data by the central and local Chinese Governments. The units of discharged Pollutants and water consumption are developed based on relevant statistical data for simulation. This model constructed is available to simulate the rates of evapotranspiration, penetration, runoff, and river flow rates, especially peak flow rates. Simulated BOD, DO, nitrogens, phosphorus and suspended solids in the Weihe River agreed well with measured ones. It is estimated that water quality in the Weihe River would be improved when the ratio of wastewater treatment reaches 80%/