Optimization Of Slope-separated Terrace Structure And Its Water Catchment And Storage Measures In Hilly And Gully Region On The Loess Plateau

Slope-separated terrace is one of the important measures to develop high-efficiencyagriculture of soil and water conservation. It’s a scientific problem that how to optimize theslope-separated terrace structure and its water catchment and storage measures when thosemeasures built. So in this paper, a physical model of slope-separated terrace was constructedand the mathematical model (WEPP) was modified and validated by the measured data on thephysical model. Then the structure of slope-separated terrace and the measures of thecorrespongding water catchment and storage measures were optimized.The conclusionsshowns as follows:1. The physical model of slope-separated terracecould provide necessary parametersfor mathematical model. Aiming at the promble that the mathematical modelwas diffcult to beverified due to the limited measured data, a physical model of slope-separated terrace wasbulit, on which the processes of soil erosion and nutrient migration were simulated byartificial rainfall.Then the measured runoff, sediment, soil moistureand soil availablephosphorus(A-P) loss were provided for WEPP mode verification.The results showed that therunoff on slope-separated terrace was significantly positive to rainfall intensity and thesediment showed a significantl positive correlation with flux, which was consistent with theexisted results. The soil moisture increased with the distance from slope to flat of theterraceincreased, while the soil moisture first increased and gradually became smooth lateralong the vertical direction. The stable soil moisture was about50cm below the surfacein theflat part of terraceand the value was about1.52times of that on slope(30cm). The A-P loss onterrace was significantly related with flux, runoff and start time, but changed little along thenrunoff direction. The concentration of A-P in the runoff on terrace presented a power declinerelationship with time.The A-P loss presented a power relation with ruoff×Runoff beginingtime, and could be described by the fuction··. The loss of soil nutrientcould be simulate by combining the fuction and WEPP model.2. WEPP model verification and the secondary development. Acoording to theparametres provided by the physical model, the initial crop conditions database and watercatchment area database were establishedbased on the existed database updata of WEPPmodel, the effective hydraulic conductivity of soil was tested and the hydraulic parameters of slope-separated terrace were simulated and verified. The results showed that the effectivehydraulic conductivity of loutu in Yangling was about21.67mm/h when the soil bulk densitywas1.3g/cm3aroundbase on fixed head soil column test. the correlation coefficient R2and theNash Model Coefficientsreached0.87and0.87respectivelybetween the simulated andmeasuredvaluesof soil water storage in0-200cm soil in apple orchard, which indicated thatthe soil water storage in0-200cm soil could be simulated by WEPP model.The yeild of applesimulated by WEPP model was close to the mean yield of5-8year’s apple, which means theyeild of apple could be simulated by WEPPmodel. The same results also occurredoncollectingflow efficiency, runoff and sediemnt yield, which indated thatthe WEPP model could be usedto simulate the hydraulic parameters of slope-separated terrace.3. The optimization of slope-separated terrace structure and the corresponding water andsediment regulation measures.The water cellar and water and sediment regulationmeasureswere optimized using the modified and verified WEPP model and the results showedthat in hilly and gully region of the Loess Plateau, the water cellarswith the whole volum of550m~3/hm~2shouldbe built for level terrace to meet the water requiremen by apple in thenormal years. The optimal terrace width to slope length, the volum of water cellarand the areaof water catchment areawere1:1.5,75m~3/hm~2and247m~2/hm~2respectively for the slope of15°of slope-separated terrace,1:1.0,95m~3/hm~2and313m~2/hm~2respectively for the slope of20°and1:1.0,80m~3/hm~2and263m~2/hm~2respectively for the slope of25°. The optimallocation of water catchment in slope-separated terrace was in the middle of the flat section.4. The modified and verified WEPP model could be used as a tool forthe optimization ofwater and sediment regulation measures for apple on terrace.