| This paper studies on a small watershed where the spatial scale of the confluence area of the watershed is much smaller than the spatial scale of the atmospheric rainfall meteorological process.The operation of the water environment system in small watersheds is mainly driven by local rainfall,with no inflow of outside diameter.During the rain period,the river has a large runoff,and the transport capacity and re-oxygenation ability are strong.During the non-rainfall period,the river runoff is small,and the river transport capacity and re-oxygenation ability are weak.The TP and organic matter transported from the land area into the river water body during the non-rainfall period may accumulate in the river bed or stagnate in the river water body,and cannot be exported in time.During the rainy season,the river has a high velocity,and the sediment is washed back by the current and returned to the water body.The transportation of TP and organic matter by rivers in small watersheds is uneven in time and space.After high-intensity rainfall periods,a large amount of silt organic nutrients are exported,which may cause the TP and organic matter nutrient concentrations of the river to rise rapidly in a short period of time and dissolve in the water Oxygen concentration decreases;during non-rainfall periods,organic nutrients and TP deposited on the bottom of the river bed will also be slowly released due to temperature changes or wind disturbances,consuming water to dissolve oxygen.The non-uniformity of the temporal and spatial distribution of organic nutrients and TP transport processes in small watersheds and rivers may lead to a persistently high concentration of organic nutrients and TP in river water bodies,depleting the water body of dissolved oxygen,water The ecosystem collapsed.Under natural conditions,the accumulation and input and output of organic nutrients and TP in small rivers,as well as the re-oxygenation and aerobic processes of water bodies,are in equilibrium.When the load of organic nutrients and TP released by human activities is large,it may cause the imbalance of the transportation process of the water environment system.Therefore,in order to control the water quality of small river basins and maintain their natural transport balance,it is necessary to fully study the transport and siltation process of the water environment system in order to formulate effective water environment control strategies.It is considered that TP is easy to adhere to the sediment in the river channel to accumulate or to accumulate with the biological metabolic waste to the bottom of the river bed,and will not be consumed.This subject studies the TP transport balance of a siltation section in the Fuxi River Basin,which indirectly reflects the process of siltation and erosion.The Fuxi River Basin is a small watershed with an area of about 3037.2 km~2.The spatial scale of the watershed is much smaller than the local meteorological rainfall scale.The silted river segment is located in the lower reaches of the basin,and the river segment is about 14.0km long.The TP transport model of runoff flood peaks in the deposition period of the river basin was established.This paper analyzes the process of TP's entrainment output with the rainfall runoff flood peak under the conditions of the distribution of rainfall in the basin from 2014 to 2017,And compares it with the TP siltation balance on the monthly time scale.(1)The analysis of the transport scale within the watershed shows that the scale of rainfall runoff flood peak transport is much smaller than that of the watershed runoff.Moreover,due to the low frequency of continuous rainfall lasting t>24h from 2014 to 2017,the sedimentation of TP in rivers need multiple runoff flood peaks formed by rainfalls to output.(2)According to the model's calculation of the annual output of TP in the basin,the average monthly output is 31,000 kg,accounting for 62.50%of the total annual output.The peak output of the runoff flood with rainfall is 19,100 kg,accounting for 38.10%of the annual total.During the rainfall period,the output of high-frequency runoff flood peaks accounts for a small proportion of the total annual output,so the annual output of the TP in the silted river section can be calculated using the monthly average runoff flow and measured concentration,accounting for about 81.14%,The output process of the model calculation is in good agreement with the output process of entrainment,scouring and siltation of the silt reach.(3)According to the analysis of daily rainfall and rainfall frequency from December to May of 2014 to 2017,the frequency of rainfall below 30mm per day is high,and the runoff flood peak has weak erosion and suction suction effect on the silted river section,the time is short,and the upstream The organic matter and TP transported are silted up in this river section.(4)According to comparing and analyzing the erosion and silting volume and monthly average output calculated by the model from June to September in 2014?2017,the results show that the erosion and silting volume of the runoff flood peak is about 60.10%of the annual total siltation,and the highest is about 94.40%The erosion and siltation of the silted river reaches the peak of runoff. |
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