| Saline water intrusion is one of main factors impacting water supply in dry season at the Pearl River estuary. Safeguarding water supply has become a significant social problem concerning economy development and people's living standards in this region. Rational reservoir operation, which is designed to increase runoff at estuary in dry season, is a key approach to solve water shortage problem in dry season at the Pearl River delta. However, both the dynamic processes at the Pearl River estuary and water resource system of its upstream basin are very complex. Dispatching water from upstream reservoirs to suppress saline water faces many complex problems such as long route, large span, wide range, long duration, numerous influence factors and high precision requirement. Therefore, searching rational reservoir operation method in dry season for supplementing freshwater to repulse saline water by considering the Pearl River estuary and its upstream basin as a whole, is an extremely urgent problem. Based on this, further summarizing of rules and characteristics of slat tide at the Pearl River estuary is present in this paper. A digital watershed model of the Pearl River basin is proposed and applied on discussing its hydrological characteristics in dry season. Rational reservoir operation method is studied for optimized the result of supplementing freshwater to suppress saline water. The main conclusion and innovative achievement of this paper are listed as follows:1. The characteristics of runoff effecting on saline water intrusion at Modaomen estuary were analyzed firstly. And then, we clearly propound that the upstream runoff should be divided into three regions to investigate the dominant discharge of freshwater supplement. The response relationship of salinity to tide variation is also analyzed, a selection method searching for the best opportunity to begin water supplement is proposed. A methodology of science was suggested that the best time to begin water supplement is the time corresponding with weighted daily lowest tidal level at Sanzao hydrological station.2. The applicability of the model at sectional watershed was illustrated and demonstrated basing on the integrated analysis of digital watershed model principle and particular geological, geomorphologic and hydrological conditions of the sectional watershed. A digital watershed model, which is suitable for Longtan-Wuzhou section, is built up for the first time, and can be applied on runoff analysis in these areas.3. The rules and characteristics of runoff variation at Wuzhou in dry season are studied. The response pattern of the runoff discharge at Wuzhou to Longtan discharge at dry season is obtained by using numerical experiment.4. A comprehensive prediction model of dispatching scheme is established basing on regional runoff forecast by using the digital watershed model. The prediction model is composed of three levels; those are dispatching preparedness for different level years, long-period prediction for month or ten-days and short-period modification for real-time rainfalls. These three different scale models are mutual combined with each other and cascade modified layer-by-layer.5. Dispatching preparedness and dispatching water amount for different level years in dry season are simulated and discussed. A prediction method of water dispatching for month or ten-days is proposed, detailed scheme and key factors are also provided. Short-period rotational correction on dispatching scheme according to real-time rainfall data is achieved by using our model. Furthermore, a set of scientific methods and analysis tools, which are suitable for rational reservoir operation for supplementing freshwater to suppress saline water at the Pearl River estuary, have been preliminarily established.
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