Hydrology Response In Different Scales Using Surface Water And Groundwater Coupling Model

Water is one of the most precious natural resource,upon which mankind depends forsurvival.The Water Framework Directive adopted by the European Union prescribes that waterresources management strategies must be developed at catchment scale - the natural geographicaland hydrological unit - instead of according to administrative or political bounds and theecological state of both surface- and groundwater must be considered.The catchment or basinscale is also used as the management scale in the concept of Integrated Water ResourcesManagement (IWRM) that is widely adopted as the management principle in developingcountries.The catchment or basin scale is also used as the management scale in the concept ofIntegrated Water Resources Management (IWRM) that is widely adopted as the managementprinciple in developing countries.In water circle,there is one-way or two-way transformationbetween rainfall,surface water,unsaturated flow and ground water,while surface water andgroundwater separation method in active water resources evaluation separate the complicativetransformation between surface water and ground water.In a word.Integrated Water ResourcesManagement (IWRM) will be a trend of Chinese water resource management in the future.A number of modeling tools have been developed over the past decades with quite diversityin complexity and in how the individual hydrological processes are represented.Water dynamicsin the unsaturated zone is one of the most important processes as it controls model precision.One of the limitations in using a catchment model based on a Richards' equation formulation isthe huge amount of parameters required to run the model.Using Richards' equation as themodeling platform for unsaturated flow simulations at catchment scale increase thecomputational demand,as small spatial and temporal discretizations are required in thenumerical approximation of the equation.Given these complications a relevant questiontherefore arises whether simpler and less demanding modeling approaches will provide same results or perhaps even better at catchment scale?Global climate change and human activities (land use change) have a great effect on thehydrological circle.To one study area,different land use and scale have an effect on hydrologicalcircle;to different study areas,and different climate and land use conditions have an effect onhydrological circle.Aiming at the problem,MIKESHE software developed by DHI (Danish hydrology institute),which represent a state-of-art of distributed hydrological model,is used to establish surface waterand ground water coupling model of Skjern catchment,and standard parameterization andcalibration of the model has been done.The objective of this study is to test and analyze theeffect of using different models for unsaturated flow on the dynamic response of an integrateddistributed hydrological model and analyzes effect of different climate and land use condions onhydrological circle.The effect of different unsaturated flow models on dynamic response of afully-distributed hydrological modelBased on soil database of Denmark,Pedo-transfer-functions (PTFs) are used to derive hydraulicparameters of soil.From surface to 30cm depth,there are 4 types of soil,from 30cm to 70cm,there are 2 types of soil,from 70cm to 300cm,there are 3 types of soil,and 24 combinations ofsoil are obtained through ARCGIS software in order to describe the heterogeneity of unsaturatedzone in Skjern catchment.Aiming at the problems,5 unsaturated models have been established:TLM (Simple two layer water balance model for the root zone and instantaneous routing ofthe excess water to water table)RI2 (Richards' equation -simple parameterization)R124 (Richards' equation -parameterization determined on the basis of pedo-transferfunctions and detailed soil maps)RIBP ( Richards' equation with bypass to accommodate for spatial variability)RIGR (Simplified version of Richards' equation only considering gravity flow)The results show that four kinds of unsaturated flow model have the same seasonalcharacters,in spring and winter,the rainfall is plentiful,the groundwater recharge and riverdischarge is big,while in summer and autumn,the rainfall reduced,the groundwater recharge andriver discharge decreased.The hydrological response of bypass flow model and gravity flow modelis quicker than two layers model and Richard equation model,which the simulated groundwaterlevel and discharge of bypass flow model and gravity flow model have a good agreement with theobservations,the simulated groundwater level and discharge of Richard equation model and twolayer model have a time-lag compared with observations,one reason is the sand covers main areaof Skjern catchment,macropore exist,and preferential flow occurs.The groundwater recharge andriver discharge of two layers model is bigger than the other three models.Compared simulatedeffect of four unsaturated conceptual models,Nash and Sutcliffe coefficient (R2),Root MeanSquare Error (RMSE),Correlation Coefficient (R) are chosen as model performance criteria,thesimulated results of two layers model are the most similar to the observations in four unsaturated conceptual models,and further more it is the most simple one which needs the shortest computertime,therefore two layer model is more fitable for Skjern catchment.The effect of land use change on water balance components such as groundwaterrecharge,evapotranspiration and groundwater dynamic responseSeveral land cover scenarios in the upstream area of Skjern catchment were developed by theextreme land use/cover method.Based on those land cover scenarios,MIKESHE model was usedto predict the possible hydrological variations resulted from land cover change.Results also showthat afforestation in the Skjern catchment might raise evapotranspiration and reduce runoff,and cutdown and delay flood peaks effectively.Conversion from forests to grassland,grain,heather andhomestead covers tends to reduce evapotranspiration and increase runoff volume.This invariablycould make flood peaks increase and appear in advance.Site scale and Catchment scale combinations in Skjern catchmentActual evapotranspiration,percolation,recharge and groundwater level fluctuations weresimulated for a period of twenty years (1990-1999) using EARTH and MIKESHE models Theresults of EARTH model represent one dimensional site scale,while MIKESHE model representcatchment scale.Both models appear to simulate the slow groundwater level fluctuations of thestudy area with high accuracy from 1990-1999.However,the simulated result of EARTH modelis a bit higher than the observed data probably as a result of it does not consider groundwaterabstractions.Nearly identical actual evapotranspiration and groundwater recharge values wereobtained from the simulation results of both models.The goodness of fit between the observedand simulated groundwater levels is also equally good for both models.It is recalled that bothmodels share the same boundary conditions.Hence it can be concluded that the water balancecalculation is depending more on the top boundary conditions than on the complex soil waterflow in the unsaturated zone.In general the actual evapotranspiration for forest is lower than forgrass and heather.On the contrary,recharge values below forest is almost the same as grass andheath lands.This shows that in forested areas,evaporation of intercepted rainfall contributessignifcantly to the total loss of water due to evapotranspiration causing recharge to be small.Theclose agreement between the simulated results of the two models also indicates that the simpleEARTH model is equally suitable as the more complex MIKESHE model at least for thecondition of the Skjern catchment.Comparing the hydrology response of groundwater in Skjern catchment and theNorth China plaina.Different climatic conditionsDenmark is warm climate,of which mean annual precipitation is 700-800 mm.The greatestrainfall comes between September and November.The Hebei plain is a semi-arid to semi-humidarea with a monsoon-dominated climate.Mean annual precipitation is only 500-800 mm.ofwhich more than 80% occurs in the months of June through September.The groundwaterrecharge of Skjern catchment mainly concentrated from September to November,while of theNorth China Plain mainly from June to September if not considering the effect of irrigation.b.Different groundwater depth When water table is shallow,Infiltration reaches groundwater relatively quickly,so thatmost of the individual rainfalls correspond to isolated infiltration recharge events with very smalltime-lags,the peak time-lag is about one or two days.As the depth to groundwater increases,the correspondence between rainfall and rechargedecreases;the recharge events produced by individual rainfalls merge into one single annualprocess although a few peaks of recharge correspond to large rainfall events or concentratedrainfall clusters.When water table is deep,Infiltrated water takes a long time to reach groundwater table sothe peak time lags here are 18 to 35 days even longer.c.Different land use considering crop rotationIn spring barley,winter wheat,maize and grass,the average annual actual evaportranspiration ofspring barley is the smallest one about 384.8mm,and its average annual groundwater recharge isthe biggest one about 255.1 mm in 4 types of crops.The groundwater recharge of maize is higherthan winter wheat in Skjern catchment and the North China Plain.d.Different irrigation methodIn Skjern catchment,the annual irrigation is about 60 mm.The groundwater recharge fromirrigation is a small part occupied in total rainfall and irrigation.In the North China Plain,theannual irrigation is about 300-450 mm.The simulation results show that groundwater recharge decreased significantly and thatrecharge caused by irrigation in the Hebei Plain accounted for 27-49% of the total precipitationand irrigation.Irrigation-induced recharge at Luquan was largest among the five sites (49% ofthe total precipitation and irrigation).Recharge caused by irrigation in the piedmont plain wasfound to be slightly larger than that in the alluvial and lacustrine plainInnovations1.The hydrological response of four unsaturated conceptual models is compared incatchment scale.The applicability of these models are analyzed which enrich theexperience of distributed hydrological models.2.Based on high resolution DEM and soil database,Distributed hydrological models ofSkjern catchment established which coupling the surface water and groundwater.Pedo-transfer-functions (PTFs) have been used to derive soil hydraulic parameters incatchment scale which is benefit for describing soil heterogeneity in Skjern catchment.3.Combine the results of Denmark and China,the effect of different climatic conditionsand land use on hydrological response was analyzed.