Schmidt, Sebastian

[["dc.bibliographiccitation.firstpage","750"],["dc.bibliographiccitation.journal","Journal of Hydrology"],["dc.bibliographiccitation.lastpage","763"],["dc.bibliographiccitation.volume","511"],["dc.contributor.author","Schmidt, Sebastian"],["dc.contributor.author","Geyer, Tobias"],["dc.contributor.author","Guttman, Joseph"],["dc.contributor.author","Marei, Amer"],["dc.contributor.author","Ries, Fabian"],["dc.contributor.author","Sauter, Martin"],["dc.date.accessioned","2018-11-07T09:41:13Z"],["dc.date.available","2018-11-07T09:41:13Z"],["dc.date.issued","2014"],["dc.description.abstract","The conduit system of mature karstified carbonate aquifers is typically characterised by a high hydraulic conductivity and does not impose a major flow constriction on catchment discharge. As a result, discharge at karst springs is usually flashy and displays pronounced peaks following recharge events. In contrast, some karst springs reported in literature display a discharge maximum, attributed to reaching the finite discharge capacity of the conduit system (flow threshold). This phenomenon also often leads to a non-standard recession behaviour, a so called \"convex recession\", i.e. an increase in the recession coefficient during flow recession, which in turn might be used as an indicator for conduit restricted aquifers. The main objective of the study is the characterisation and modelling of those hydrogeologically challenging aquifers. The applied approach consists of a combination of hydrometric monitoring, a spring hydrograph recession and event analysis, as well as the setup and calibration of a non-linear reservoir model. It is demonstrated for the Auja spring, the largest freshwater spring in the Lower Jordan Valley. The semi-arid environment with its short but intensive precipitation events and an extended dry season leads to sharp input signals and undisturbed recession periods. The spring displays complex recession behaviour, exhibiting exponential (coefficient alpha) and linear (coefficient beta) recession periods. Numerous different recession coefficients a were observed: similar to 0.2 to 0.8 d(-1) (presumably main conduit system), 0.004 d(-1) (fractured matrix), 0.0009 d(-1) (plateau caused by flow threshold being exceeded), plus many intermediate values. The reasons for this observed behaviour are the outflow threshold at 0.47 m(3) s(-1) and a variable conduit-matrix cross-flow in the aquifer. Despite system complexity, and hence the necessity of incorporating features such as a flow threshold, conduit-matrix cross-flow, and a spatially variable soil/epikarst field capacity, the developed reservoir model is regarded as relatively simplistic. As a number of required parameters were calculated from the hydrogeological analysis of the system, it requires only six calibration parameters and performs well for the highly variable flow conditions observed. Calculated groundwater recharge in this semi-arid environment displays high interannual variability. For example, during the 45-year simulation period, only five wet winter seasons account for 33% of the total cumulative groundwater recharge. (C) 2014 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.jhydrol.2014.02.019"],["dc.identifier.isi","000335274900065"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/33682"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","1879-2707"],["dc.relation.issn","0022-1694"],["dc.title","Characterisation and modelling of conduit restricted karst aquifers - Example of the Auja spring, Jordan Valley"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","177"],["dc.bibliographiccitation.journal","Journal of Hydrology"],["dc.bibliographiccitation.lastpage","190"],["dc.bibliographiccitation.volume","502"],["dc.contributor.author","Schmidt, Sebastian"],["dc.contributor.author","Geyer, Tobias"],["dc.contributor.author","Marei, Amer"],["dc.contributor.author","Guttman, Joseph"],["dc.contributor.author","Sauter, Martin"],["dc.date.accessioned","2018-11-07T09:18:41Z"],["dc.date.available","2018-11-07T09:18:41Z"],["dc.date.issued","2013"],["dc.description.abstract","Karst groundwater resources in semi-arid environments are highly vulnerable with respect to anthropogenic impacts, such as wastewater infiltration, because of focussed recharge and the rapid transport of dissolved substances in highly permeable conduit systems. In this study, groundwater resources of the western margin of the Lower Jordan Valley and their respective water qualities were investigated. The region is characterised by a carbonate aquifer system, which predominantly discharges via karst springs. The area experiences a large population growth and consequently a rising chloride concentration due to effluent infiltration is observed in many springs. Long-term records of chloride concentration in spring water were assembled in an extensive literature study. For some springs, larger parts of the period of 1938-2012 were covered. Chloride was used as an all-in-one environmental tracer for the objectives of (1) groundwater recharge estimation and (2) anthropogenic impact quantification. The investigations required the determination of the natural background concentration of chloride in groundwater. It was estimated by a combined use of historical data and a trend analysis for larger springs in the area and a range between 20 and 40 mg l(-1) was found. Together with chloride concentration data for local precipitation, the long-term mean natural groundwater recharge was calculated with the chloride mass balance method. Recharge ranged between 25% and 50% of the precipitation. The proportion of wastewater-borne spring flow was quantified by a chloride end member mixing model. The springs exhibited a wastewater-borne flow fraction between 0% and 20% calculated from recent samples. The successful application of these methods underlines the value of long-term monitoring, even at a comparatively low time resolution. (C) 2013 Elsevier B.V. All rights reserved."],["dc.identifier.doi","10.1016/j.jhydrol.2013.08.009"],["dc.identifier.isi","000326768100017"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/28459"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","1879-2707"],["dc.relation.issn","0022-1694"],["dc.title","Quantification of long-term wastewater impacts on karst groundwater resources in a semi-arid environment by chloride mass balance methods"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]