>Magister Scientiae - MSc / In the Kruger National Park (KNP) which is the flagship conservation area in South Africa, the impact on groundwater should be kept to a minimum as groundwater plays a vital role in sustaining ecosystem functioning and sustaining baseflow to streams and rivers. For this reason groundwater has been recognized as one of the environmental indicators that need to be monitored. The KNP has adopted a Strategic Adaptive Management (SAM) approach with clear ecosystem management goals. The achievement of these goals is evaluated by using environmental indicators. These indicators are evaluated against thresholds of potential concern (TPC). TPCs are a set of boundaries that together define the spatiotemporal conditions for which the KNP ecosystem is managed. TPCs are essentially upper and lower limits along a continuum of change in selected environmental indicators. Historically, groundwater recharge and surface water interaction with rivers has tended to be overlooked in the KNP. This study proposes a conceptual model of groundwater recharge processes in the KNP, defining when and how groundwater recharge occurs. Two methods were used, the Cumulative Rainfall Departure (CRD) and stable isotopes of ²H and ¹⁸O. An adapted version of the CRD which incorporates a long and short term memory of the system was used to identify possible recharge processes. Further, using the CRD method a reliable reconstruction of the long term groundwater level trends are simulated using monthly rainfall totals with reference to the average rainfall over the entire time series 1936-2009. The stable isotope of ²H and ¹⁸O samples from cumulative rainfall samplers, surfacewater (streams and rivers) and groundwater from boreholes were collected monthly for approximately one year (May 2010 to July 2011). The isotope composition of the groundwater was used to establish whether recharge was immediate or delayed. Additionally, the isotopic composition of surface-water from rivers and streams were compared to that of groundwater to identify surface-water interactions. Groundwater recharge in KNP occurs during the rainy summer months (December to March) and very little to none during the dry winter season (April to September). Recharge takes place during rainfall sequences 100mm or more. The stable isotope records collected from cumulative rainfall, groundwater and surface water (streams and rivers) indicate that groundwater experiences evaporation prior to infiltration. As the KNP experiences high evaporation rates, insignificant rainfall sequences contribute little or zero to recharge. The CRD analysis of groundwater level fluctuations shows that recharge to the aquifers respond to dry and wet cycles that last for 6 to 14 years. The KNP experienced several periods of below-average rainfall and hence no significant recharge took place to the basement aquifers. During a normal rainy season the water levels rise somewhat then starts receding again. It is only during major rainfall events that may occur every 100yrs to 200yrs causing the aquifers to fully recharge. This was perfectly illustrated by the high groundwater levels after the 2000 major rainfall event that recharged the aquifers fully. During below average rainfall years the overall water level trend is drastically declining. The system experiences higher natural losses than gains due to outflow of groundwater to streams and rivers. The KNP is divided down the center by two geological formations, granites along the west and basalts along the east. The combination of the CRD model and the stable isotopic analysis suggest that the dominant recharge processes that occur in the southern region of the KNP are direct recharge via piston flow and indirect recharge via preferred pathways particularly streams and rivers. Along the eastern half of the KNP on the Basalts and Rhyolite direct recharge via piston flow are dominant. Groundwater is not recharged via small streams and rivers (Sweni and Mnondozi Rivers) as it was found that at these particular sites these rivers are detached and do not interact with groundwater. Along the western granitic areas the dominant recharge process are indirect recharge. Recharge takes place via preferred pathways particularly streams and rivers. It was found that ephemeral rivers (Nwatsisonto River) act as sinks for groundwater recharge and influent-effluent conditions are experienced along seasonal rivers (Mbyamiti River). The large perennial Sabie and its tributary the Sand River are consistently fed by groundwater, above all maintaining base flow during the dry season. These rivers act as basin sinks receiving groundwater discharge all year round. Using the stable isotope composition of rainfall, surface-water and groundwater to act as a natural tracer, in combination with the CRD method proved invaluable to confirm the plausible recharge processes. The study provided a conceptual understanding of the groundwater system in the KNP forming the foundation to developing acceptable limits (TPCs) of the groundwater levels in the KNP. The model will serve as a guide for the recharge processes and for deciding on the location and time frames for data collection to ultimately set TPCs for groundwater in the KNP to sustainably manage the resource.

<p>Topography is one of the primary drivers of physical processes in the rivers and floodplains. Advances in remote-sensing and survey techniques have provided high-resolution representation of the floodplains but information regarding the 3D representation of river channels (commonly known as river bathymetry) is sparsely available. Field surveys along an entire river network in a watershed remains infeasible and algorithms for estimating simple but effective characterization of river channel geometry are hindered by an incomplete understanding of the role of river bathymetry in surface and subsurface processes. </p> <p> The first objective of this dissertation develops an automated framework – System for Producing RIver Network Geometry (SPRING) for improving the geospatial descriptors of a river network. The tool takes as input the DEM and erroneous river centerline to produce spatially consistent river centerlines, banks, and an improved representation of river channel geometry. SPRING can process entire river networks and is not limited single reach applications. The proposed framework is flexible in terms of data requirements, resolution of output datasets and user preferences. It has a user-friendly graphic user interface (GUI) and is appropriate for large-scale applications since it requires minimal user input.</p> <p> A better understanding of the role of bathymetric characteristics in surface-subsurface hydrology and hydrodynamics can facilitate an efficient incorporation of river bathymetry in large river networks. The second objective explores the level of bathymetric detail required for accurately simulating surface and subsurface processes by developing four bathymetric representations using SPRING with reducing level of detail. These bathymetric configurations are simulated using a physically based tightly coupled hydrologic and hydrodynamic model to estimate surface and subsurface fluxes in the floodplains. Comparison of fluxes for the four bathymetric configurations show that the impact of river bathymetry extends beyond surface routing to surface water – groundwater interactions. Channel conveyance capacity and thalweg elevation are the most important characteristics controlling these interactions followed by channel side slope and channel asymmetry. </p> <p> The final objective aims to develop benchmarks for bathymetric characteristics for accurately simulating flooding related physical processes. The sensitivity of surface and subsurface fluxes to error in channel conveyance capacity is investigated across reaches with varying geomorphological characteristics. SPRING is used to create six bathymetric configurations with varying range of error in channel conveyance capacity (ranging from 25% to 300%). They are simulated using a tightly coupled physically distributed model for a flood event and the estimates of water surface elevation, infiltration and lateral seepage are compared. Results show that incorporating channel conveyance capacity with an error of within 25% significantly improves the estimates of surface and subsurface fluxes as compared to those not having any bathymetric correction. For certain reaches, such as those with high drainage area (>1000km²) or low sinuosity (< 1.25), errors of up to 100% in channel conveyance capacity can still improve H&H modeling.</p>

The Swedish municipalities of Gävle and Älvkarleby need new sources of drinking water as the population grows. Gästrike vatten AB has employed the consultant firm Midvatten AB to assess the possibility of a new groundwater extraction site on the Uppsala esker between Älvkarleby and Skutskär in northern Uppland county. It has been observed that the natural recharge to the aquifer in the Uppsala esker might be too low to compensate for a future groundwater extraction and that there is a risk of induced infiltration from the river Dalälven if the water table is lowered. River water might bring organic contaminants into the aquifer and negatively affect the groundwater quality.A solution proposed by Midvatten is to infiltrate the esker with river water free from organic contaminants at infiltration sites. This artificial infiltration is estimated to create new groundwater to compensate for the extraction and stop river water from reaching the extraction wells. There is however, a need to estimate the magnitude of infiltrating river water when the infiltration sites are active.The aim of this study was to estimate the flow of water between the river and a section of the Uppsala esker for a test period during 2017, specifically, the infiltration from the river. In addition to this, changes in flow depending on proposed pumping and infiltration scenarios were modelled.A MODFLOW model was developed in the graphical user interface Groundwater Modeling System (GMS) and its performance was validated against observed aquifer head. The model could accurately represent the head close to the river but was less accurate with increasing distance from the river. Average infiltration from the river varied from 3 to 25 l s-1. The calculated infiltration depended on which extraction well or artificial infiltration site was active and the rate of flow.It was concluded that the distribution of hydraulic conductivity in the aquifer was not sufficiently detailed. A solution could have been to use stratigraphic data from borehole logs instead of a general quaternary deposits map as basis for the distribution of hydraulic conductivity. Artificial infiltration close to the river prevented large volumes of induced infiltration. The accuracy of the model could have been improved if the results were compared to other methods such as particle-tracking, tracer tests and with measurements of the streambed such as seepage meters. / Gävle och Älvkarlebys kommuner är i behov av nya grundvattentäkter för att kunna försörja invånarna med dricksvatten i framtiden. Ett område som är av intresse för de två kommunerna är ett grundvattenmagasin i Uppsalaåsen intill Dalälven mellan Älvkarleby och Skutskär. Vid ett dricksvattenuttag kan vattenbalansen i magasinet ändras. I magasinet uppskattas grundvattenbildningen vara för låg för att pumpa upp nog mycket vatten och bibehålla en stabil dricksvattenförsörjning. När uttaget av grundvatten är högre än grundvattenbildningen sänks grundvattenytan och vatten flödar från andra delar av magasinet eller älven för att kompensera. Älvvattnet bedöms ha en stark hydraulisk koppling med grundvattnet, vilket innebär att det finns en risk att älvvattnet infiltrerar i magasinet och sänker kvalitén på framtida dricksvatten.Konsultföretaget Midvatten AB har i uppdrag att bedöma möjligheten till ett framtida dricksvattenuttag. Midvatten har som lösning anlagt stationer med sprinklerinfiltration för att i framtiden kunna infiltrera avhumifierat älvvatten som på sikt omvandlas till grundvatten. Denna konstgjorda infiltration är också tänkt att hindra älvvatten från att ta sig in i magasinet genom att förse magasinet med den mängd vatten som går förlorad av dricksvattenuttag. Hur mycket älvvatten som tar sig in till grundvattenmagasinet och når brunnarna vid ett framtida uttag och konstgjord infiltration, är dock oklart.Syftet med denna studie var att uppskatta flödet mellan åsens grundvattenmagasin och Dalälven och specifikt infiltrationen av älvvatten. Detta gjordes genom att utveckla en digital MODFLOW-flödesmodell i programmet GMS. Modellen kunde, med hjälp av uppmätta vattennivåer i grundvattenmagasinet och älven, räkna ut hur mycket vatten som flödade in från älven (infiltrerade). Den uträknade infiltrationen låg i genomsnitt på 3-25 l s-1. Infiltrationsmängden berodde på vilken brunn som vattnet pumpades ur, hur mycket som pumpades ut och hur mycket artificiell infiltration som tillfördes i de tre infiltrationsområdena under en period av 2017. Modellen användes även till att uppskatta flödet från älven för 28 tilltänkta scenarier under 2017 med konstant pumpning och konstgjord infiltration i de olika brunnarna och infiltrationsstationerna.Resultaten visade att modellen kunde uppskatta grundvattenmagasinets vattennivåer nära älven men inte på längre avstånd ifrån älven. Detta berodde på att magasinets hydrauliska parametrar inte var korrekt fördelade. Fördelningen kunde ha förbättrats om de baserats på jordarter från borrprotokoll istället för en jordartskarta. Modellen visade att mycket lite älvvatten flödar in i akviferen om vatten artificiellt infiltreras nära älven. För att resultaten av den här studien ska bli tillförlitliga krävs det att resultaten jämförs med andra metoder som använder sig av förslagsvis partikelspårningsmodeller, spårämnesstudier eller flödesmätningar av flodbädden.