Effects Of Recycled Water Regulation And Low Impact Developments On Water Quality Of Urban River

As a crucial component of urban areas, urban river plays multiple roles including water supply sources, flood and drainage prevention, landscapes, etc. Rapid urbanization and human activities yield insufficient drainage capacity, water scarcity, and serious pollution for many rivers. How to make full and effective use of reclaimed water recharge and low impact development are keys for water quality control and mechanism studies of urban rivers. The primary goal of this study is to explore the effects of reclaimed water recharging and low impact developments on water quality of Tangxi river by using mathematical models. It would provide theoretical supports and decision-making basis for water quality control and mechnism studies of unban rivers.1) Firstly, fuzzy pattern recognition, comprehensive pollution index method and system clustering method were adopted to explore the spatial and temporal variation patterns of water quality in Tangxi river. Results showed that the overall quality of Tangxi river belonged to moderate to severe levels of pollution, and nitrogen and phosphorus were the primary pollutants to Tangxi river; Tangxi river exhibited obvious seasonal pattern, with the highest CPI of spring; the spatial boundary between moderate and severe levels of water quality was Ziyun road, to which from Yulong road was moderate level and from Huizhou road was severe level;2) Secondly, to investigate the effects of reclaimed water recharge on water quality of urban river, one-dimensional hydrodynamic and water quality models, in combination with fuzzy pattern recognition technique, were developed to explore how the location, quality and quantity of reclaimed water recharging regulate water quality of urban river. Application to the Tangxi River in Hefei showed that the reclaimed water recharge shaped hydrodynamic characteristics and pollutants loads, as well as their diffusion and degradation processes, thus affecting spatial distribution of river water quality; the most significant impacts occurred around the supplement location. Fuzzy pattern recognition analysis revealed that the supplement of reclaimed water at the upstream had more significant positive impacts on river water quality, and enhanced quality and quantity of reclaimed water can further advance water quality of urban river;3) Finally, this study focused on the effects of bio-retention and initial rainwater storage ponds on water quality of urban landscape river, where the SWMM model was adopted to simulate rainfall-runoff of the watershed of Tangxi River, in combination with one-dimensional hydrodynamic and water quality models of the river. The results indicated that application of bio-retention ponds increased rainwater infiltration and delayed the peak flow, thus reducing the surface runoff and yielding the reduction rates of pollutants at the Huizhou dam ranging from 5.8% to 70.6% under the storm events with various return periods. Compared with the bio-retention ponds, the initial rainwater storage ponds exhibited much better performance on reducing the peak flow and pollutants into the river, with the pollutant reduction of 43.4%～71.9% for various return periods. Nevertherless, the reduction effects of both LID strategies would gradually decreased with further increase in the return period. The combination of these two LID measures could lead to better effects for urban river regulation.