ANNUAL VARIATIONS IN GROUND-WATER TEMPERATURE AS A TRACER OF RIVER-AQUIFER INTERACTIONS
Open Access
- Author:
- Moret, Geoffrey John Maxted
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 20, 2007
- Committee Members:
- Richard Rudolph Parizek, Committee Chair/Co-Chair
Charles James Ammon, Committee Member
Derek Elsworth, Committee Member
Demian Saffer, Committee Member
Kamini Singha, Committee Member - Keywords:
- hydrogeology
temperature - Abstract:
- In recent years, annual and diurnal variations in aquifer temperature have increasingly been used to investigate surface-water-ground-water interactions. This thesis represents three separate but related investigations into the value of annual temperature in characterizing and quantifying infiltration from surface-water bodies. Currently, there is a great deal of interest in the exchange between the Rio Grande and the underlying aquifer in Albuquerque, New Mexico so that surface stream depletion can be properly estimated. The USGS has collected temperature time series in a series of piezometers along a profile perpendicular to the river to characterize horizontal flow. The current method for interpreting these data is to calibrate a 2-D numerical model of the aquifer, a process that can be time-consuming. We propose that a simple 1-D analytical solution can be used to estimate horizontal flux through an aquifer based on temperature variations. This analytical model does not fully represent all of the factors that contribute to aquifer temperature signals, but in many cases it may represent the system sufficiently well to produce a useful estimate of ground-water flux. At the Mohawk River site near Schenectady, NY, a large number of wells drilled to characterize induced infiltration have permitted spatially extensive measurements of the annual variation in aquifer temperature. These data show a zone of high temperature variation caused by a plume of infiltrated river water pulled towards municipal supply wells. The aquifer at the site is highly transmissive, so we developed a method-of-characteristics, particle-tracking code to model the advection-dominated thermal transport. Our model of the site shows that the plume of high temperature variation is caused by aquifer thickening over a known bedrock depression. The annual temperature variation data were also sensitive to the magnitude and spatial variation of the riverbed conductance. The results of this study suggest that numerical modeling is required to fully understand temperature data collected in aquifers with complex geometries. If the spatial distribution of temperature measurements is sufficiently dense, then high transmissivity zones acting as preferential flow paths for infiltrated surface-water can be identified. A limitation of this method is that ground-water temperature can be measured only in wells or in natural discharge points. For some shallow aquifers, however, this temperature reversal can be seen in temperature measurements taken in shallow soil borings. By collecting temperature data in a large number of shallow soil borings, preferential flow paths in shallow soil borings can be mapped. In this paper we model soil temperature variations, investigate the range of conditions under which aquifer temperature variations can be detected, and demonstrate the technique with a data set from a site along the Mohawk River near Schenectady, New York.