Date of Award

12-2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor(s)

Laura K. Lautz

Keywords

alpine meadows, groundwater, heat tracing, stream restoration, surface water, tropical glaciers

Subject Categories

Earth Sciences

Abstract

Interactions between surface water and groundwater impact both the quality and quantity of water resources. This dissertation is focused on the interactions between surface water in streams and groundwater in hyporheic zones and shallow fluvial aquifers, and how human beings influence these interactions and are influenced by them. The three chapters of this dissertation span scales from cm to km and locations from Upstate New York to the Peruvian Andes, but are united by the goal to improve the scientific understanding of groundwater-surface water interactions (GWSWI) using novel techniques, in order to improve the outcomes of human activities for people and ecosystems.

Heat is a useful tracer for quantifying GWSWI, but analyzing large amounts of raw thermal data has many challenges. Chapter 1 presents a computer program named VFLUX for processing raw temperature time series and calculating vertical water flux in shallow sub-surface-water systems. The workflow synthesizes several recent advancements in signal processing, and adds new techniques for calculating flux rates with large numbers of temperature records from high-resolution sensor profiles. The program includes functions for quantitatively evaluating the ideal spacing between sensor pairs, and for performing error and sensitivity analyses for the heat transport model due to thermal parameter uncertainty. The new method is demonstrated by processing two field temperature time series datasets collected using discrete temperature sensors and a high-resolution DTS profile. The analyses of field data show vertical flux rates significantly decreasing with depth at high-spatial resolution as the sensor profiles penetrate shallow, curved hyporheic flow paths, patterns which may have been obscured without the unique analytical abilities of VFLUX.

Natural channel design restoration projects in streams often include the construction of cross-vanes, which are stone, dam-like structures that span the active channel, and are often thought to increase local hyporheic exchange. In Chapter 2, vertical hyporheic exchange flux (HEF) and redox-sensitive solutes were measured in the streambed around 4 cross-vanes with different morphologies. Observed patterns of HEF and redox conditions are not dominated by a single, downstream-directed hyporheic flow cell beneath cross-vanes. Instead, spatial patterns of moderate (

Melting tropical glaciers supply approximately half of dry season stream discharge in glacierized valleys of the Cordillera Blanca, Peru. The remainder of streamflow originates as groundwater stored in alpine meadows, moraines and talus slopes. A better understanding of the dynamics of alpine groundwater, including sources and contributions to streamflow and GWSWI, is important for making accurate estimates of glacial inputs to the hydrologic budget, and for our ability to make predictions about future water resources as glaciers retreat. The field study described in Chapter 3 focused on two high-elevation meadows in valleys of the Blanca. Tracer measurements of stream and spring discharge and groundwater-surface water exchange were combined with synoptic sampling of water isotopic and geochemical composition, in order to characterize and quantify contributions to streamflow from different geomorphic features. In a valley headwaters study site, groundwater supplied approximately half of stream discharge from the meadow, with most originating in a debris fan adjacent to the meadow and little from the meadow itself (6%); however, in at a mid-valley study site, where meadows are extensive, local groundwater has a large impact on stream flow and chemistry through large net discharge and fractional hydrologic turnover.

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