Study On The Underlying Surface Change Of Haihe River Basin And Its Impacts On Flood

The influence of human activities on runoff is currently a hot issue. Humanactivity, including agriculture, forestry, industrialization, urbanization and the waterconservancy project construction, as a result, the impact of these human activitieschanged the watershed underlying surface, therefore, the impacts of underlyingsurface changes on runoff and flood are objective existence. In Haihe River basin thehuman activity influence on watershed underlying surface mounting, lead to obviouschanges that have taken place in watershed underlying surface conditions for decades,resulting in rainfall and flood attenuation in flood season, caused flood productiondecrease under the same rainfall condition and a sharp reduction in river basin waterresources. Delineating the hydrological type regions of Haihe River basin, and takingthe typical watersheds in hydrological type regions of Haihe River basin as researchobjects, we analyzed the underlying surface factor changes of typical watersheds, andcarried out the variation analysis of storm and flood, identified the change points, thenstatistically analyzed the the impacts degree of underlying surface changes on floods.The rainfall-runoff evolution characteristics of Luanhe River basin and typicalwatersheds, the rainfall-runoff model was established basing on the underlyingsurface factors, and the influences degree of underlying surface changes on differentlevel floods was calculated. The main research contents and results were as follows:(1)Based on the hydrological underlying surface factors, including remotesensing monitoring data of geomorphology, vegetation and the surface permeable rate,et. al, and the measured climate data, the underlying surface and climate factors ofHaihe River basin were identified and used to do multiple superimposed andcompound analysis in GIS. According to the similarities and differences of units todelineate hydrological type regions, and Haihe River basin is divided into sevenhydrological type regions. Then we discussed the impacts of land use change and unitbasin scale on hydrologic regions and chose typical watersheds in some of them.(2)Based on the land use remote sensing data in different period of Haihe Riverbasin, we analyzed the land use area variation trends and transfer between differenttype of land use in Fuping, Xitaiyu and Lengkou watershed. In each watershed, theland use changed a lot1970-1980and2000-2006, mainly transferred between farmland forest and grassland, and changed little1980-2000. Through investigation,analyzed soil and water conservation measures and size of key soil and waterconservation area in Haihe River basin and typical watersheds, collected groundwatermining information in mountainous area, and estimated the groundwater mininginfluence on basin’s soil moisture storage capacity.(3)For the time series of typical watershed’s storm volume, flood volume, floodpeak and flood peak delay time, Using linear trend regression and Mann-Kendall rankcorrelation test for trend analysis, adopting sequential clustering method, double masscurve and nonparametric pettitt test to test the jump points, and determining theaberrance points of storm and flood characteristics through comparing with measuredrainfall and runoff data. Selecting floods under similar rainfall before and afterunderlying surface change, and the characteristic changes of each flood were analyzed,preliminary results suggest that, underlying surface changes can result in flood peakand volume reducing, and make flood hydrograph homogenizing.(4)Using qualitative and quantitative change theorem based on variable fuzzysets, aberrance point test analysis was carried out for times series of annual rainfalland runoff in6sub-basins of Luanhe River basin and time series of flood peak, floodvolume and flood peak delay time in Fuping, Xitaiyu and Lengkou watershed,compared with nonparametric pettitt test result that the result is reasonable and themethod is available. Analyzing the evolution characteristics of annual rainfall andcorresponding runoff series, and flood processes under similar rainfalls, and it showsthat, the human activities is the main factors which cause runoff reduction and thegradually qualitative change of runoff series, and underlying surface changes result inattenuation of flood peak, runoff volume and runoff coefficient, the graduallyqualitative changes will occur to flood processes when the attenuation rate reaches acertain extent.(5)A distributed hydrological model was established, which consideredunderlying surface changes such as groundwater level change, land use change andsoil and water conservation projects, and respectively considered the differences offlow production elements such as evaporation and infiltration on each land use type,adopted excess infiltration-saturation combined runoff model to calculate the runoffon different land use areas, used unit hydrograph to calculate surface water confluenceand in the meantime considered water storage capacity and catchment area of soil andwater conservation projects such as small reservoir and check dam, adopted linear reservoir method to calculate the confluence of interflow and groundwater runoff. Themodel parameters were calibrated and verified, and the shapes of simulated floodhydrograph and measured flood hydrograph were fitting good, the model can be usedto analyze underlying surface impact degree on flood characteristics.(6)Adopting the distributed hydrological model we have established, the floodprocesses in underlying surface conditions that before and after1980were simulatedrespectively. Comparing simulate results, we obtained the comprehensive effect onflood caused by underlying surface change including land use changes and soil andwater conservation project, etc., and the respective effect of land use changes,groundwater level change and soil and water conservation projects. In Fuping, Xitaiyuand Lengkou watershed, underlying surface changes cause flood peak and floodvolume reduced, in general, the changes of flood peak and volume caused byunderlying surface changes decrease with the increase in flood volume. The changesof flood peak and volume caused by groundwater level falling are little, and theaverage reduction proportion is not more than3%. The impact of land use change onwatershed flood volume depends on the land use change extent. Soil and waterconservation has the reducing effect both on flood peak and flood volume, and thereduction extent of flood peak and volume caused by underlying surface changesdecrease with the increase in flood volume.