DELINEATING CRITICAL RECHARGE AREAS IN KARST TERRAIN: SPRING CREEK WATERSHED CASE STUDY
Open Access
- Author:
- Newman, Josiah Scott
- Graduate Program:
- Agricultural and Biological Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 08, 2014
- Committee Members:
- James Michael Hamlett, Thesis Advisor/Co-Advisor
- Keywords:
- Spring Creek
ArcMap
ArcGIS
Groundwater Recharge
Karst
Critical Recharge
Recharge
Infiltration - Abstract:
- A local source of readily available drinking water is necessary for any sustainable society. In many areas, groundwater is the common source of drinking water for individual residences and small communities. Identification of the source of groundwater is imperative for the protection of drinking water. By identifying areas of groundwater recharge on the surface, actions can be taken to protect the quality of water that becomes groundwater. This study focused on identifying critical recharge areas in the Spring Creek watershed in Centre County, Pennsylvania using geographic information systems (GIS). Previous GIS studies concerning recharge have focused on groundwater resource development and exploitation and focused on deep geologic features. The Spring Creek watershed is karstic and prone to sinkhole development. The goal of this study was to identify surface areas that are most likely to provide infiltrated water that could become groundwater recharge. Two different modeling approaches were used to address the research goal. A previously published modeling technique was used to incorporate several thematic layers into a groundwater recharge map. Among the published GIS-based models for identifying groundwater recharge zones, the model developed by Yeh et al. (2009) was selected for this work because it provided a detailed methodological description. This model identified and weighted five factors affecting groundwater recharge potential: geology (lithology), land use, lineaments, drainage, and slope. These data layers were combined to produce a resultant groundwater recharge potential zone map. A second approach used the techniques described in Technical Release 55 (TR-55) by the Natural Resources Conservation Service (NRCS) for evaluating runoff in small, urbanized watersheds. The infiltration potential model was used to estimate runoff as a function of a twenty-four hour storm over five different return periods. In this research, rainfall that did not become runoff was considered as infiltration water. The infiltration potential model results were combined with datasets describing tributary areas to sinks and sinkholes and impervious surfaces to develop a set of composite maps delineating potential surface runoff areas that most directly contribute to recharge. Using the Yeh et al. (2009) approach, a composite recharge area map of the Spring Creek watershed was developed. While the resultant map generally identified areas of high recharge potential, it did not incorporate known karstic features such as sinks and sinkholes. The Yeh et al. (2009) approach also heavily relied upon lineament data that was not fully digitized across the Spring Creek watershed. This study revealed limitations in directly using a model developed for a different geographical setting. For instance, in the karstic Spring Creek watershed, consideration needs to be given to sinks and sinkholes. The major limitation is the need to customize, for the specific area under consideration, the factor weighting values and scores used to characterize the relative influence of data layers on recharge potential. Additionally, the large variability in the quality and quantity of the available supporting data can potentially compromise the accuracy or completeness of specific data layers. The developed composite maps from the infiltration potential model more reasonably identified surface infiltration potential areas in the Spring Creek watershed primarily because of the inclusion of surface features and the exclusion of features that are associated with deep recharge such as geology and fractured bedrock. Subsurface features were excluded to create surface infiltration potential mapping intended to be used as part of a larger recharge model. The model also considered sinks and sinkholes which are primary features of the karstic nature of the Spring Creek watershed. One disadvantage of this approach is that it treats all non-runoff water as recharge/infiltration and effectively ignores evapotranspiration losses, which can be large in forested areas. A major outcome of this study is model composite maps that indicate the source of infiltrated water across the Spring Creek watershed. A valuable observation made through conducting this study is the importance of distinguishing deep recharge models (e.g. the Yeh model) from infiltration potential models, and the necessity of selecting an appropriate model for the watershed to be evaluated. The model composite maps produced by this study may be used to inform decisions on wellhead protection, water quality, and emergency response plans in local municipalities. The infiltration potential model composite maps produced by this study are intended to be used as part of a more complex potential groundwater recharge model. The composite maps are to be used as infiltration potential mapping, which assumes that water infiltrates beyond the soil horizon. Combining these surface infiltration potential areas and areas tributary to sinks/sinkholes with deep recharge models through the use of groundwater contours would allow for the delineation of surface features to points of interest below the surface and vice versa. Combining the mapping in this manner would provide a three-dimensional mapping that provides specific source areas, allows for accurate volume calculations, and gives more detailed information related to groundwater protection.