Thesis (M.S.)--Brigham Young University. Dept. of Geological Sciences, 2007. / Includes bibliographical references (p. 38-41).

Doctor of Philosophy / Department of Civil Engineering / David Steward / Western Kansas has a semi-arid climate where the demand for water resources is greater than the natural supply. To meet the demand for irrigated agriculture, the groundwater has been extracted at a rate greater than the natural recharge rate, resulting in declining water table in the aquifer and reduced streamflow in the rivers and streams in the region. An assessment of the rivers in western Kansas was conducted to determine the fluxes between the river, groundwater, and the atmosphere. Riverbeds were instrumented to determine the conductivity of the riverbed sediments, the transmission losses of the Arkansas River were modeled to determine the interactions between the surface water and groundwater, and the evapotranspiration of the Arkansas River corridor was estimated using satellite remote sensing to quantify of water lost to the atmosphere. The Arkansas River and Cimarron River are shown to have a high hydraulic conductivity and a large infiltration capacity at the surface of the riverbed. However, the large surface infiltration capacity does not translate into large transmission losses, which are a fraction of the rate of the surface infiltration capacity of the riverbed. Thus, surface infiltration is only one factor of what controls the transmission losses. It is shown that transmission losses for a connected river-aquifer system are driven by induced infiltration by riparian vegetation. The interactions between the surface, groundwater and atmosphere were assessed over time, revealing that the flux to the atmosphere can be decoupled from the Arkansas River discharge and the groundwater recharge. While the declining discharge in the Arkansas River can be attributed to the extraction of groundwater resources and the management of surface water resource, the atmospheric fluxes are independent of the surface water and groundwater at an annual scale. When the river ecosystem is water stressed, the trees continue to draw water. This points to both the reliable store of water from the alluvial aquifer and the ability of the tree community to respond to water stress. While the water in the alluvial deposits are currently being lost from the system through evapotranspiration, this provides a potential store for consideration in future water management decisions.

MESHWR / Department of Hydrology and Water Resources / This study was focused on determining groundwater recharge and groundwater potential for Mhinga area in South Africa, which is a rural area that depends mainly on groundwater for domestic water supply. Numerical modelling was used to simulate the groundwater behaviour in the aquifer and estimate groundwater recharge. MIKE SHE and MIKE 11 models were coupled and used to estimate groundwater recharge within calibration and validation periods of 2007/07/01 to 2009/12/31 and 2010/01/01 to 2013/05/21, respectively. Due to limited data availability for Mhinga, modelling was carried out at quaternary scale and then localised to Mhinga area. Remotely sensed data (satellite images, shapefiles and maps) was used to produce the groundwater potential map for Mhinga. The data were assigned with weights using Saaty’s Analytical Hierarchy Process and overlain on ArcGIS platform. Borehole drilling statistics of the boreholes in A91H quaternary catchment were used to validate the groundwater potential map. In streamflow modelling using MIKE 11, values of Nash-Sutcliffe efficiency (NSE), correlation coefficient (R), root mean square error (RMSE) and mean absolute error (MAE) were 0.51-0.89, 0.73-0.97, 3.61-7.96 and 1.13-2.75, respectively. In integrated groundwater modelling using MIKE SHE, values of NSE, R, RMSE and MAE were 0.72-0.84, 0.87-0.93, 0.18-0.32 and 0.13-0.26, respectively. These values showed that MIKE SHE and MIKE 11 models had satisfactory performances. Groundwater recharge estimates were generally very low ranging from 0 to 2.75 mm/year, which constituted 0 – 0.42 % of Mean Annual Precipitation (MAP) for the A91H quaternary catchment. This was associated with high evapotranspiration (mean of approximately 4 mm/day) compared to the low precipitation levels (MAP of 656 mm/year). Moreover, in the low lying areas, with gentle slopes, low recharge between 0.2 – 0.4 mm was observed. The groundwater potential (GWP) map produced revealed that Mhinga is predominantly covered by regions of very low and low groundwater potential, which was associated with the type of geology. Area coverages of 34.47 % had very low, 51.39 % had low, 7.66 % had moderate and 6.48 % had high groundwater potential. Moderate to high groundwater potential zones were located along the geologic fault zones. In A91H, 112 unsuccessful boreholes were drilled, 69 (61.6 %) fell in the very low GWP zones, 16 (14.3 %) fell in the low GWP zones, 17 (15.2 %) fell in moderate GWP zones and 10 (8.9 %) fell in the high GWP zones. In the Mhinga, 19 unsuccessful boreholes were drilled of which, 11 (57.9%) fell in the very low GWP zones, while 6 (31.6%) fell in the low GWP zones and 2 (10.5%) fell in the moderate GWP zone. Hence 89.5% of all the unsuccessful boreholes drilled occurred in the very low to low GWP zones. It is concluded that the study area is mainly dominated by of areas with low recharge and very low to low groundwater potential. It is recommended that the MIKE SHE – MIKE 11 model and the GIS models should be developed further and improved as more data is collected to refine the conceptualisation of the aquifer.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Hydrogeology. July 2017. / Hydrogeological research was undertaken in the transboundary Ramotswa dolomitic aquifer to provide understanding and quantification of the processes governing recharge mechanism and rates, in order to promote efficient and sustainable groundwater resource utilization and development, as well as to improve the Ramotswa transboundary aquifer management. Hydrochemical and tracer approaches were utilized to evaluate the processes governing the recharge mechanism while the chloride mass balance approach was further applied to assess groundwater recharge rates. Results indicated that all groundwater samples contained detectable amounts of tritium highlighting the renewability of the transboundary Ramotswa aquifer resources. Two distinct water types were characterised: sub-modern waters approximately recharge prior to the 1950s and a mixture of modern and sub-modern waters of recently recharge rainfall indicative of active recharge in the area through intensive rainfall. Correlation between δ18O and δ2H, and soil Cl- indicated that groundwater recharge in the Ramotswa dolomitic aquifer takes place mainly by two flow mechanisms: a displacement of moisture through a diffuse or piston flow through permeable soils and from concentrated runoffs due to surface depressions, and a preferential flow component through fractures that outcrop at surface and riverbed infiltration along the ephemeral Notwane River. Annual groundwater recharge estimates varied from 0.4% MAP to 12% MAP and from 5% MAP to 14% MAP within the northern parts and the southern parts of the study area, respectively. Recharge estimates correlated well with the proposed mechanism of flow both in the southern and in the northern parts of the study area as well as with the previous studies conducted within the greater Ramotswa area. A way forward to ensure the long-term sustainability of the transboundary Ramotswa aquifer resources is recommended, such as to preserve and protect potential recharge areas through carefully controlled land use planning and development, and to equate abstraction rates to average recharge rates, which has to be subjected to the Limpopo Watercourse Commission. / MT2018

A mathematical model is proposed to estimate annual recharge rates from various sources into an aquifer, based on chemical and isotopic data. The aquifer is divided into mixing cells. For each mixing cell, annual mass balance equations are written which express the conservation of water, dissolved chemicals, and stable environmental isotopes. These equations are solved simultaneously for unknown recharge rates by quadratic programming. A similar approach was used earlier to estimate inflows into a river reach which acts as a single mixing cell. The sensitivity of the model to input errors is analyzed by applying it to synthetic data corrupted by artificial noise. The ability of the model to deal with real data is illustrated by applying it to the semiarid Aravaipa basin in southern Arizona.

No description available.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1986. / Includes bibliographical references (leaves 164-170).

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Riparian areas are valuable resources, particularly in semi-arid areas where water is usually scarce and rapid streamflow responses to runoff are common. Only recently has the importance of in-channel recharge during high streamflow periods ("floods") been recognized in rivers with gaining and losing reaches where recharge processes and flowpaths can be very complex. This dissertation builds upon this recent work by investigating how three factors influence how riparian systems respond to floods over a range of temporal and spatial scales. First, the impact of differences in local hydrogeologic forcings are investigated at the seasonal and 50 meter-reach scales. Second, the significance of flood event size and duration is studied at the multi-year and river (~50 Km) scale. Third, an underlying mechanism behind how changes in bed sediment composition can influence stream-aquifer interactions at the event- and point-scales is developed. Major findings of this work include observations along the Upper San Pedro River of seasonal floodwater storage below moderately gaining reaches and longer-term storage below losing reaches (seasonal to multi-year depending on the nature of the riparian groundwater flow system). The longest and largest floods (with respect to flow volume) dominate floodwater recharge in the Bill Williams River and an apparent flood size and duration threshold exists. This threshold must be met or exceeded in order for individual events to induce observable amounts of recharge that can then influence the amount and composition of later streamflow. This threshold agrees with the process presented here involving preferential mobilization and deposition of fine bed sediment particles--which dictate hydraulic conductivity--during each event that would lead to disproportionately more recharge during large floods. Forecasts of increased precipitation intensity and decreased annual precipitation in some regions, including the southwestern United States, due to changes in the earth's climate are likely to make floods a more important driver of riparian hydrologic processes. Consequently, the work presented here and other process-based studies of how floods influence riparian hydrology and water quality will be useful in making well-informed decisions regarding riparian preservation, management and restoration as human demands and the global climate change in the future.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2017. / A study on groundwater recharge and processes controlling recharge was conducted in the Upper Crocodile catchment, located in the Johannesburg region. The catchment extends from the water divide south of Johannesburg, to the Hartbeespoort Dam in the North-West Province. The study area is predominantly underlain by the crystalline basement and meta-sedimentary rocks. The Upper Crocodile catchment is classified as a semi-arid region, receiving a mean annual rainfall of 699.3 mm/yr. Groundwater recharge was quantitatively and qualitatively assessed using the water balance, baseflow separation, water table fluctuation and environmental isotope methods. The water balance and the baseflow separation methods resulted in recharge amounts of 4 and 5.8% of mean annual rainfall, respectively. The water table fluctuation method was only applied to the dolomitic aquifer and yielded a mean annual recharge estimate of 14% of the mean annual rainfall. Application of the isotopic shift method, which makes use of isotopically enriched water samples, resulted in a recharge amount of 10.19 to 23.90 mm/month obtained for the quartzites of the Witwatersrand Supergroup, south of the study area. Tritium was used to determine the residence time of stream water samples, collected during winter to represent baseflow. Additionally, it was used to understand the range of groundwater contribution to streams. The tritium values revealed that there are three types of water; i) relatively old water with lower tritium values, ii) intermediate tritium values indicating the possibility of mixing of older groundwater with more recent recharge and iii) high tritium values suggesting contamination from a local source/recent rainwater. The results of groundwater recharge from the quantitative methods showed a temporal and spatial variability of recharge; this was attributed to the different processes that govern groundwater recharge. Climate appeared to have the most influence on potential groundwater recharge, with rainfall controlling the temporal variability of recharge while land cover, soil characteristics and geology influenced the spatial distribution of groundwater recharge. Approximately 153 x 106 m3/yr of wastewater was discharged into streamflow from wastewater treatment works as of 2008. The wastewater flow into streams overshadowed the baseflow contribution. The consequence of the presence of wastewater was reflected in the overestimation of groundwater recharge. / LG2017