Date of Award

2016

Document Type

Open Access Master's Report

Degree Name

Master of Science in Geology (MS)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

John S Gierke

Committee Member 1

Zhen Liu

Committee Member 2

David Watkins

Abstract

Where the proper geological and hydrological conditions exist, natural springs have provided a reliable source of clean water to mankind for eons. Changing climates and land development can negatively impact spring source replenishment and threaten their reliability as a source of water. In the face of prospects of diminishing supplies and increasing population demands, community leaders question whether and how to invest in development for enhancing sustainability and protecting water quality, causing water managers to dispute their reliability given decreasing flows. Springs located in the rugged jungle of western Panama serve as the primary water supply for many indigenous communities, such as Candela, which hosts a population of 140. The author of this report lived in that remote community for two years working with the water committee leaders to develop their spring-dominated water supplies. With a lack of data and the physical understanding of the hydrological principles, people often speculate when making water and land use decisions. Objective observational data from monitoring and computational tools for simulating system hydrology would be a valuable platform from which to hold more reasoned discussions on climate impacts and land use to enhance the reliability of water sources. This report characterizes the hydrologic conditions within the watershed that contribute to spring discharge and uses numerical modeling to test hypotheses related to the aquifer mechanics supplying the spring flow. Observations and measurements made within the watershed area included soil conditions, spring flows, and local weather (precipitation and temperature). The data were evaluated using various analytical and numerical methods in an attempt to understand the spring discharge processes relative to the local precipitation. The topography of the catchment area was extrapolated from DigitalGlobe imagery. Soil data analysis provided estimates of infiltration, runoff and recharge rates, which all affect water availability in the shallow groundwater aquifer supplying the springs. A baseflow recession analysis of the combined spring discharge data was performed to quantify the flow behavior of the hydrograph and offer predictions of drought flow behavior. Hydrologic inputs and outputs of the system were accounted for using a basic catchment-scale water budget that produced an annual recharge rate given the variable environmental conditions. These estimates were applied to two groundwater flow models using GMS MODFLOW-2000, each with different aquifer dimensions. The hydraulic conductivity and storativity of the aquifers were calibrated in transient-state simulations to the flow conditions observed during the dry season. Various climatic scenarios were then applied to the models to evaluate their accuracy of simulated flow to the observed flow and to predict water availability from the springs. Simulations using a thicker aquifer outperformed those using a thinner aquifer by having less flow error and more flexibility under a range of hydrologic conditions. Not only do the parameters defining the aquifer properties control the flow rate, but the volume of storage also plays a seminal role in matching the observed spring behavior within these models. The results suggest that the model aquifer presented here requires substrate that has large enough interstitial storage capacity to accumulate a substantial amount of water, yet exhibits flow paths tortuous enough to slowly release water over time. With plenty of recharge during the wet season, spring discharge is sustained throughout the long dry season by a combination of high infiltration rates of the soil and aquifer material, and sufficient aquifer storage volume and retention.

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