Study On Distributed Runoff-Sediment Coupled Model In Nanliujiang Based On RS/GIS And SWAT Model

Beibu gulf is the south gate of our country and is the marine outfall of the southwest area recently. In recent years, with the adjustment of industrial structure,the surface coverage have taken place drastic changes in the area, and it is urgent to assessment the effects on the ecological environment. Along with the rising of the beibu gulf economic zone as the national development strategy, the importance of Nanliujiang basin is becoming more and more get the attention of the people.Therefore, this paper by dint of RS/GIS technology,based on the Mann-Kendall test method, the RUSLE model and the SWAT model, discusses the precipitation and temperature changes and its impact on hydrological processes in the Nanliujiang basin.In addition, in this paper, the soil erosion is evaluation in the study area and the watershed’s distributed runoff-sediment coupled model is established. At the end of the article, Nanliujiang runoff and sediment variation characteristics are simulated.Through the research, in this paper, the main conclusions are as follows:1. Through the collection of meteorological and hydrological data, using describing statistical analysis and the M-K test method analysis found that rainfall was roughly in balance and the temperature has a rising trend, in addition to the mutation has occurred around 1967, during the period of 1961 to 2008, and the runoff and sediment has a downward trend. The runoff and the sediment significantly influenced by the climate, and the determination ratio of regression equation is more than 0.8 between rainfall and runoff.2. The soil erosion of Nanliujiang watershed is slight erosion with the RUSLE model to evaluate the status of soil erosion, the average soil erosion modulus is 1390t/km2?a, the yearly amount erosion is 1032.83 × 104t/a. Moreover, research finding that:(1) the mainly source of soil erosion are nonirrigated farmland, woodland, the reason is that a large number planting of sisal hemp, cassava, sugar-cane and eucalyptus.(2)In the range of 0~400 meters above sea level, the soil erosion intensity first climb up then decline.(3)The soil erosion have a strongly influence by vegetation coverage, the smaller vegetation coverage, the greater erosion area.3. Based on SWAT model,the runoff and sediment variation characteristics under monthly scale are simulated. In the select 20 parameters, including the CN2, ESCO,OV_N, etc, respectively the sensitivity analysis of runoff and sediment, study found that runoff on CN2, ALPHA_BNK, GW_DELAY, ESCO and REVAPMN parameters is more sensitive, however, sediment on CN2, USLE_P, SOL_AWC, CH_K2,SLSUBBSN parameters is more sensitive. After the sensitivity parameters calibration and test, the R2 and the NS coefficient is above 0.8 both in the calibration and validation periods, and the result showed that the runoff and sediment simulationeffect is very efficient with the established model.4. Based on the RUSLE model and the SWAT model contrast found that both have their advantages. For runoff simulation can rely on the SWAT model, in the sediment transport simulation, however, can first through evaluation of RUSLE model,after satisfactory results, then put the value of R, K, C and P from the RUSLE model adjust input to the SWAT model to simulate. That can greatly improve the efficiency of parameter calibration and simulation.