(河海大学水利水电学院,江苏南京210098)
关键词：河岸带;洪水;地下水水位;沙槽试验;数值模拟
河岸带指河水-陆地交界处至河水影响消失为止的地带(riparianzone)[1]。河岸带是受河水水位影响显著的陆地生境,具有独特的空间结构和生态功能,是陆地水文循环的重要组成部分[2]。在河岸带,河流与地下水之间的相互作用密切,两者通过河道岸坡进行水分和物质交换,从而影响河岸地区生物地球化学过程。
野外观测中,由于各研究的实验环境不同,观测结果具有较强的区域性,很难将结果应用于其他流域。河岸带地表水与地下水的作用过程受到流量、河床形态、沉积物渗透性、岸坡坡度等诸多因素的影响[3],很难对影响因子进行人为的调控,从而得到在单一因子影响下的河岸地下水与河水的交换规律。Boano等[33]提出,研究动态条件下的潜流过程要简化模型突出动态因子对于地表水地下水交换过程的影响。
1.1试验沙槽
为模拟河流地表水和河岸带地下水的相互作用,试验在如图1所示的循环水槽装置中进行。循环系统由蓄水箱、水位控制室和沙槽组成。蓄水箱中的水通过水泵进入水位控制室,水位控制室中间设有溢流平台,当周围的水位高于溢流平台的上平面时,多出的水会由溢流槽回流到蓄水箱中。溢流平台通过步进电机与控制端相连,通过调整溢流平台的高度来控制水位。试验中由于水分蒸发量很小,忽略不计,沙槽除连接控制室的一侧外均为无流边界。
图1试验循环水槽装置
试验主要考虑了河道水位变动对河岸带横断面的影响。沙槽长度为8m,高1.2m,宽0.16m。沙槽装填高度0.8m的人工石英砂,颗粒大小较均匀,中值粒径为0.7mm,饱和渗透系数为3.88×10-3m/s,孔隙度为0.4。根据vanGenuchten[37]公式,非饱和土壤的形状参数α和n分别取11m-1和6。水位控制室和沙槽之间设有0.9m的连接段,使水流在进入沙槽时更加平稳。沙体岸坡为竖直边坡,为防止水流掺杂沙粒流失并稳定沙坡,在沙槽与连接段之间安装了透水隔板。沙槽内部设置有10个压力传感器,实时记录试验过程中沙槽内的压力数据,压力传感器每隔5s自动记录测点压力,测量精度为±1mm,埋设位置见图1(a)。
1.2水位信号
(1)
图2试验用洪峰脉冲信号
1.3试验步骤
每组试验结束后,控制溢流平台使其下降至最低位置,关闭水泵并打开回水阀门,使沙槽中的水缓慢排出,确保沙槽中水位下降到较低的位置,不影响下组试验的进行。所有工况的试验过程中,均无泥沙启动情况。
本文基于Voss等[39]的研究成果建立河水和河岸带地下水相互作用的非饱和二维模型,控制方程为
(2)
根据vanGenuchten[37]提出的经验公式,非饱和土壤的水力参数由式(3)～(4)确定:
(3)
(4)
式中:α和n分别为形状参数;KS为饱和渗透系数;SWres为残余饱和度。
3.1洪水作用下的河岸带地下水的波动规律
图3洪峰前后瞬时水头及流速分布数值模拟结果
图4距河岸不同距离的地下水水位过程试验和数值模拟结果对比
图5河岸地下水的水平和垂直流速变化数值模拟结果
图6质点运动轨迹数值模拟结果
3.2不同峰值洪水对河岸带地下水的影响
图7不同峰值洪水作用下的地下水水位过程试验结果
图8不同峰值洪水作用下的岸坡流量过程数值模拟结果
3.3不同历时洪水对河岸带地下水的影响
a.洪水作用下,河岸带地下水水位的波动沿程呈指数形式衰减。水位上升和下降过程表现出显著的不对称性,水位上升较快而下降较慢,对洪水过程的响应具有滞后性,且随距河岸距离的增加而更明显。
b.河岸带各点地下水水位的波动随洪峰的增大而增强,同时岸坡上的流通量增加,河水和地下水的交换量增大,峰值的变化对于地下水水位滞后性的影响并不明显。
本文研究了单峰脉冲洪水信号对河岸带地下水动力过程的影响,但受水力调控、蒸发、降雨等影响,实际潜流带的交换过程动态性更强,非规则信号作用下的地下水波动规律尚需明确。另外,本文基于垂直岸坡,而天然河道中大部分河岸具有一定的坡度,因此不同河岸形态影响下的地下水动力过程还有待进一步研究。
参考文献：
[1]陈吉泉.河岸植被特征及其在生态系统和景观中的作用[J].应用生态学报,1996,7(4):439-448.(CHENJiquan.Riparianvegetationcharacteristicsandtheirfunctionsinecosystemsandlandscapes[J].ChineseJournalofAppliedEcology,1996,7(4):439-448.(inChinese))
[2]夏继红,严忠民.生态河岸带研究进展与发展趋势[J].河海大学学报(自然科学版),2004,32(3):252-255.(XIAJihong,YANZhongmin.Advancesinresearchofecologicalriparianzonesanditstrendofdevelopment[J].JournalofHohaiUniversity(NaturalSciences),2004,32(3):252-255.(inChinese))
[3]HARVEYJW,BENCALAKE.Theeffectofstreambedtopographyonsurface-subsurfacewaterexchangeinmountaincatchments[J].WaterResourcesResearch,1993,29(1):89-98.
[4]KASAHARAT,WONDZELLSM.Geomorphiccontrolsonhyporheicexchangeflowinmountainstreams[J].WaterResourcesResearch,2003,39(1):1-14.
[5]SAVANTSA,REIBLEDD,THIBODEAUXLJ.Convectivetransportwithinstableriversediments[J].WaterResourcesResearch,1987,23(9):1763-1768.
[6]HESTERET,DOYLEMW.In-streamgeomorphicstructuresasdriversofhyporheicexchange[J].WaterResourcesResearch,2008,44(3):1-17.
[7]SILLIMANSE,BOOTHDF.Analysisoftime-seriesmeasurementsofsedimenttemperatureforidentificationofgainingvs.losingportionsofJudayCreek,Indiana[J].JournalofHydrology,1993,146:131-148.
[8]BOANOF,REVELLIR,RIDOLFIL.Quantifyingtheimpactofgroundwaterdischargeonthesurface-subsurfaceexchange[J].HydrologicalProcesses,2009,23(15):2108-2116.
[9]CARDENASMB,WILSONJ,ZLOTNIKVA.Impactofheterogeneity,bedforms,andstreamcurvatureonsubchannelhyporheicexchange[J].WaterResourcesResearch,2004,40(8):1-14.
[10]PACKMANAI,BROOKSNH.Hyporheicexchangeofsolutesandcolloidswithmovingbedforms[J].WaterResourcesResearch,2001,37(10):2591-2605.
[11]ELLIOTTAH,BROOKSNH.Transferofnonsorbingsolutestoastreambedwithbedforms:theory[J].WaterResourcesResearch,1997,33(1):123-136.
[13]KRAUSES,BOANOF,CUTHBERTMO,etal.Understandingprocessdynamicsataquifer-surfacewaterinterfaces:anintroductiontothespecialsectiononnewmodelingapproachesandnovelexperimentaltechnologies[J].WaterResourcesResearch,2014,50(2):1847-1855.
[14]GUC,HORNBERGERGM,HERMANJS,etal.Effectoffreshetsonthefluxofgroundwaternitratethroughstreambedsediments[J].WaterResourcesResearch,2008,44(5):1-12.
[15]WESTHOFFM,GOOSEFFM,BOGAARDT,etal.Quantifyinghyporheicexchangeathighspatialresolutionusingnaturaltemperaturevariationsalongafirst-orderstream[J].WaterResourcesResearch,2011,47(10):DOI10.1029/2010WR009767.
[16]ARNTZENEV,GEISTDR,DRESELPE.Effectsoffluctuatingriverflowongroundwater/surfacewatermixinginthehyporheiczoneofaregulated,largecobblebedriver[J].RiverResearchandApplications,2006,22(8):937-946.
[17]STOREYRG,HOWARDKW,WILLIAMSDD.Factorscontrollingriffle-scalehyporheicexchangeflowsandtheirseasonalchangesinagainingstream:athree-dimensionalgroundwaterflowmodel[J].WaterResourcesResearch,2003,39(2):1-17.
[18]WROBLICKYGJ,CAMPANAME,VALETTHM,etal.Seasonalvariationinsurface-subsurfacewaterexchangeandlateralhyporheicareaoftwostream-aquifersystems[J].WaterResourcesResearch,1998,34(3):317-328.
[19]WONDZELLSM,SWANSONFJ.Seasonalandstormdynamicsofthehyporheiczoneofa4th-ordermountainstream.I:hydrologicprocesses[J].JournaloftheNorthAmericanBenthologicalSociety,1996(1):3-19.
[20]CZIKOWSKYMJ,FITZJARRALDDR.EvidenceofseasonalchangesinevapotranspirationineasternUShydrologicalrecords[J].JournalofHydrometeorology,2004,5(5):974-988.
[21]LOHEIDESP,LUNDQUISTJD.Snowmelt-induceddielfluxesthroughthehyporheiczone[J].WaterResourcesResearch,2009,45(7):DOI:10.1029/2008WR007329.
[22]MATHIEUR,BARIACT.Anisotopicstudy(2Hand18O)ofwatermovementsinclayeysoilsunderasemiaridclimate[J].WaterResourcesResearch,1996,32(4):779-789.
[23]张光辉,费宇红,田言亮,等.暴雨洪水对地下水超采缓解特征与资源增量[J].水利学报,2015,46(5):594-601.(ZHANGGuanghui,FEIYuhong,TIANYanliang,etal.Characteristicsofalleviatingtheover-exploitationanditsrechargeontherainstormfloodtotheshallowgroundwaterinthesouthernplainofHaiheRiverBasin[J].JournalofHydraulicEngineering,2015,46(5):594-601.(inChinese))
[24]DUDLEY-SOUTHERNM,BINLEYA.Temporalresponsesofgroundwater-surfacewaterexchangetosuccessivestormevents[J].WaterResourcesResearch,2015,51(2):1112-1126.
[25]SHIBATAH,SUGAWARAO,TOYOSHIMAH,etal.Nitrogendynamicsinthehyporheiczoneofaforestedstreamduringasmallstorm,Hokkaido,Japan[J].Biogeochemistry,2004,69(1):83-104.
[26]MOUWJE,STANFORDJA,ALABACKPB.Influencesoffloodingandhyporheicexchangeonfloodplainplantrichnessandproductivity[J].RiverResearchandApplications,2009,25(8):929-945.
[27]徐华山,赵同谦,孟红旗,等.滨河湿地地下水位变化及其与河水响应关系研究[J].环境科学,2011,32(2):362-367.(XUHuashan,ZHAOTongqian,MENGHongqi,etal.Relationshipbetweengroundwaterlevelinriparianwetlandsandwaterlevelintheriver[J].EnvironmentalScience,2011,32(2):362-367.(inChinese))
[28]FRANCISBA,FRANCISLK,CARDENASMB.Watertabledynamicsandgroundwater–surfacewaterinteractionduringfillinganddrainingofalargefluvialislandduetodam-inducedriverstagefluctuations[J].WaterResourcesResearch,2010,46(7):W07513.
[29]HUCKSSAWYERA,BAYANICARDENASM,BOMARA,etal.Impactofdamoperationsonhyporheicexchangeintheriparianzoneofaregulatedriver[J].HydrologicalProcesses,2009,23(15):2129-2137.
[30]WONDZELLSM,SWANSONFJ.Floods,channelchange,andthehyporheiczone[J].WaterResourcesResearch,1999,35(2):555-567.
[31]GERECHTKE,CARDENASMB,GUSWAAJ,etal.Dynamicsofhyporheicflowandheattransportacrossabed-to-bankcontinuuminalargeregulatedriver[J].WaterResourcesResearch,2011,47(3):DOI:10.1029/2010WR009794.
[32]LARSENLG,HARVEYJW,MAGLIOMM.Dynamichyporheicexchangeatintermediatetimescales:testingtherelativeimportanceofevapotranspirationandfloodpulses[J].WaterResourcesResearch,2014,50(1):318-335.
[33]BOANOF,REVELLIR,RIDOLFIL.Modelinghyporheicexchangewithunsteadystreamdischargeandbedformdynamics[J].WaterResourcesResearch,2013,49(7):4089-4099.
[34]NOWINSKIJD,CARDENASMB,LIGHTBODYAF,etal.Hydraulicandthermalresponseofgroundwater-surfacewaterexchangetofloodinginanexperimentalaquifer[J].JournalofHydrology,2012,472:184-192.
[35]吕辉,赵坚,陈孝兵,等.洪水过程对垂向潜流交换作用的影响[J].水电能源科学,2015(3):4.(LYUHui,ZHAOJian,CHENXiaobing,etal.Theimpactoffloodprocessonverticalaquiferexchange[J].WaterResourcesandPower,2015(3):4.(inChinese))
[36]BOANOF,REVELLIR,RIDOLFIL.Bedform-inducedhyporheicexchangewithunsteadyflows[J].AdvancesinWaterResources,2007,30(1):148-156.
[37]vanGENUCHTENMT.Aclosed-formequationforpredictingthehydraulicconductivityofunsaturatedsoils[J].SoilScienceSocietyofAmericaJournal,1980,44(5):892-898.
[38]CARTWRIGHTN,LIL,NIELSENP.Responseofthesalt-freshwaterinterfaceinacoastalaquifertoawave-inducedgroundwaterpulse:fieldobservationsandmodelling[J].AdvancesinWaterResources,2004,27(3):297-303.
[39]VOSSCI,PROVOSTAM.SUTRA:Amodelfor2Dor3Dsaturated-unsaturated,variable-densityground-waterflowwithsoluteorenergytransport[C]//Water-ResourcesInvestigationsReport(2002-4231).VancouverWA:USDepartmentoftheInterior,USGeologicalSurvey,2002.
Impactoffloodprocessongroundwaterlevelfluctuationinariparianzone
ZHANGZeyu,YUXiayang,XINPei
(CollegeofWaterConservancyandHydropowerEngineering,HohaiUniversity,Nanjing210098,China)
Abstract：Inordertostudytheimpactofthefloodprocessongroundwaterinariparianzone,laboratoryexperimentsandnumericalsimulationswereconductedtoinvestigatethegroundwaterlevelfluctuationsubjectedtofloodswithdifferentamplitudesanddurations.Theresultsshowthatthegroundwaterlevelfluctuationwasasymmetric,thatgroundwaterrosequicklyanddeclinedslowly.Theamplitudeofthegroundwaterlevelfluctuationattenuatedwithanexponentialtrendandasignificanttimelagasthedistancefromthebankincreased.Asthefloodamplitudeincreased,thegroundwaterlevelfluctuationwasenhanced,resultinginanincreasedamountofexchangebetweentheriverwaterandgroundwater.However,thetimelagwithrespecttothegroundwaterlevelchangedslightly.Asthedurationoffloodpeaksincreased,thetimelagwassignificantlyenhanced,thegroundwaterlevelfluctuatedmoresignificantly,andittookmoretimeforthegroundwaterleveltoreturntothepre-floodstatus.
Keywords：riparianzone;flood;groundwaterlevel;flumeexperiments;numericalsimulation
DOI：10.3880/j.issn.1004-6933.2017.02.005
基金项目：国家自然科学基金(51579077)
作者简介：张泽宇(1992—),男,硕士研究生,研究方向为水力学及河流动力学。E-mail:zeyuzhang_hhu@163.com