Groundwater/stream interactions
From GeoClasses
Contents |
Abstract
The goal of this project was to take temperature and depth measurements of the Loosahatchie and use the measurements to locate areas of spring water discharge. Upon arrival at the site, near Arlington TN, shade conditions were observed along the banks. This was noted, and later investigated using the temperature data that was collected. An application-specific temperature probe was fabricated prior to our excursion. Temperature and depth readings were taken at 1-meter intervals across 3 transects of the Loosahatchie. These were graphed to illustrate possible spring discharge points and shade effects. The spring discharge locations remained elusive, but a clear shade effect was observed on bed temperature.
Introduction
Springs vary in many ways. They migrate upstream, downstream, and across the channel. Their rates of discharge change with rainfall, stream level, and other conditions. Springs influence deposition of sediment and streambed topography. By measuring the same area of the Loosahatchie as Dan Neilan did, it was hoped that the same springs mapped in his thesis could be located. Mapping of these spring discharge points during a relatively dryer period may have shed light on some of the many processes that influence spring migration.
Hypotheses tested
Two hypotheses were tested in the present study. First, could two spring discharge locations, mapped in Dan Neilan's thesis, be located again using bed and water temperature measurements? Second, could a shade effect be observed influencing stream bed temperature?
Methods
USGS and TVA internet resources were used to determine a suitable date for field measurements. The Loosahatchie needed to be at a stage low enough to wade its entire width, but not so low as to prevent measurement. Based on the annual rainfall and streamflow records attained from USGS and TVA sites, 7/23/07 was chosen as the most appropriate date for field measurements. Upon arrival at the site a piece of polymer twine marked at 1-meter intervals was staked on both sides of the bank. This reference marker was moved downstream 1 meter at a time to measure each of 3 transects. Once the bed temperature, water column temperature, and depth measurements were collected they were compiled into an excel spreadsheet.
Data collection
- Graphs of the Loosahatchie's daily discharge and gauge readings were obtained from [1] Precipitation data was obtained from [2] This data proved useful in selecting an appropriate date for field measurements of the Loosahatchie.
- Here the USGS discharge rates, river gauge levels, and TVA precipitation data from 5/1/07-7/18/07 are presented in an excel spreadsheet. Media:loosahatchie.xls
- On 7/23/07 Dr. Urbano and I took temperature and depth measurements across 3 transects of the Loosahatchie. These 3 transects correspond to meters 0, 1, and 2 of Dan Neilan's study area. Temperature readings were taken at the bed surface and (~5cm higher) in the water column at 1 meter intervals across the river. A temperature probe was fabricated specifically for this purpose. Shade conditions were noted to examine a possible effect on streambed temperature.
Data collected
Here the temperature and depth data gathered on 7/23/07 is presented in an excel spreadsheet. Media:Temperature_Profiles.xls
In column A of the spreadsheet distance from the northern bank is listed. Columns B, C, and D list bed temperature, water column temperature, and depth respectively. Column E indicates whether shade was present or not. A "1" in this column indicates shade and a "0" indicates that the area was sunlit.
Data analysis
In depth data analysis was not possible due to the limited scope of the data collection. A trend of lower temperatures towards the banks is easily observed, but this phenomenon could be attributed to many different conditions.
Results and Discussion
The data collected shows a clear tendency of lower bed temperatures directly adjacent to the bank. This tendency can be observed in the graphs of bed and water column temperature to the right.
With the current data it would be difficult to attribute this tendency solely to spring water discharge or a shade effect, because the shade effect is a confound for the spring water discharge. The drop in temperatures towards banks is probably a combination of these and other factors. The data collected for these 3 transects shows an effect, but it is inconclusive as to the cause. The previously stated hypotheses remain unsupported. Collecting data on more transects might prove useful in differentiating the effects of these phenomena.
Conclusion
USGS and TVA records of stream flow and gauge level are valuable tools when planning a field excursion to the Loosahatchie. Buried flow-meters around Arlington TN provide measures to make predictions and form hypotheses. As Dan Neilan demonstrated in his thesis, areas of spring water discharge can be mapped by temperature gradient. Unfortunately, the limited number of transects measured in the present research prevented re-mapping of the same discharge points. A shade effect was observed, but served as a confound for the lower temperatures around spring discharge points. Support or refutation of the two previously stated hypotheses remains pending the collection of more data. Increasing the number of transects studied should provide the data needed to differentiate between the effects.
Future research
Future research on this topic should measure more sequential transects in order to develop a more comprehensive map of streambed temperature. Without this, confounds like shade effects can be difficult to overcome. To aid in the location of areas of spring water discharge, measurements might be taken close to the banks for longer distances. This might serve as a sort of survey tool by which one could return to the points at which temperatures dropped.
