Research On Connotation Analysis And Simulation Evaluation Methods Of Sponge Watershed

The time-space development of river basins is easily interfered by the natural factors and human factors,and because of that,the researches,projects or managements focusing on river basins also need to change the trend along with the change of the features of river basins.The goal should be continually adjusted toward to the healthy development of river basins and Man-Water Harmony.In order to let river basin give full play to the function as the carrier of the nature-manpower duality water cycle,the effect way is to explore new ideas,promoted a better distribution and to harmonize natural resources usage and society development.The concept of"Sponge Basin" is proposed as an angle to accomplish the goal.The physical mechanism of Sponge Basin is preliminarily explored and the evaluation system is set up.The SWAT model is applied in Yongding River Basin to analyze the changes of two indexes(runoff and water conservation)by simulating in several scenarios,finally to help recover the potentiality of Sponge Basin,and to identify the advantageous factors and disadvantageous factors of Sponge Basin.1."Sponge Basin" Connotation analysisThe nature of Sponge Basin is to adjust and interfere the water cycle under Man-Water Harmony by limited human activities,and to enhance the adaptive and adjustment ability of nature.The main function is when the precipitation is rich,the basin will absorb some to reduce the runoff,and when the precipitation is poor,the storage of the basin will sustain the water supply for the human society and natural environment.The basic goal of Sponge basin is to restore the resilient storage space for water and build a natural structure to prevent water disasters.2.Explore the evaluation system of Sponge BasinThe method of evaluation is divided to two ways.The first is to analyze the long-term evolution of the river basin to generalize the trend of the development of basin.The second is to set the baseline scenario and comparing scenarios simulated by a model to analyze the respond of the chosen indexes to the whole basin,and then to evaluate the effect of the indexes.The indexes system is set according to the three properties of Sponge Basin(water absorbency,water release capability,and resilience).3.Simulate water cycle on Yongding River Basin by SWAT modelBased on the flood return period,the flood scenarios are set as 5-year probability flood,10-year probability flood,and 20-year probability flood.And the time period is set as from June to September in the year of the chosen floods.The land use of 1995 is set as the baseline scenario,and the land use of 2005 is set as comparing group(SO).The change of the agricultural land between 1995 and 2005 is set as S1.The change of the grass land between 1995 and 2005 is set as S2.The change of the construction land between 1995 and 2005 is set as S3.The transformation from all unused land to agricultural land is set as Wl.The transformation from all unused land to forest is set as W2.The transformation from all unused land to grass land is set as W3.SWAT model is applied to conduct all 8 simulations.In S series,the indexes are 1-day maxim runoff,7-day maxim runoff and the depth of runoff.In W series,the indexes are soil water content and underground recharge by soil infiltration.4.The results of runoff scenariosApart from S3 scenario,the three indexes under S0,S1,S2 all decrease.The effect from strong to weak is S1>SO>S2.In 5-year probability flood scenario,in the order of 1-day maxim runoff,7-day maxim runoff and the depth of runoff,SO decreases by-5%,-20%,-11%,comparing to the baseline scenario.Results of S1 decreases by-19%,-21%,-16%.Results of S2 decreases by-4%,-10%,-19%.Results of S3 increases by +29%,+19%,+5%.In 10-year probability flood scenario,in the order of 1-day maxim runoff,7-day maxim runoff and the depth of runoff,SO decreases by-13%0-19%,-18%,comparing to the baseline scenario.Results of S1 decreases by-19%,-21%,-16%.Results of S2 decreases by-6%,-14%,-21%.Results of S3 increases by +15%,+4%,+7%.In 20-year probability flood scenario,in the order of 1-day maxim runoff,7-day maxim runoff and the depth of runoff,SO decreases by-14%,-8%,-10%,comparing to the baseline scenario.Results of S1 decreases by-18%,-16%,-10%.Results of S2 decreases by-1%,-8%,-20%.Results of S3 increases by+13%,+9%,+2%.5.The results of water conservation scenariosThe amount soil water content under W1,W2 and W3 all increased.The effect from strong to weak is W1>W2>W3.Soil water content under W1 is 34.92mm,the one of W2 is 34.48mm and the one of W3 is 34.34mm,which are respectably added by 0.73mm,0.29mm and 0.15mm comparing to the baseline scenario.Groundwater recharge by soil infiltration under W1 is 6.09mm,the one of W2 is 6.14mm and the one of W3 is 6.15mm,which are respectably added by 0.04mm,0.09mm and 0.10mm comparing to the baseline scenario.