Project Summary
From GeoMod
Purpose: The objective is to identify groundwater discharge areas in local streams and rivers. This will be achieved by monitoring chemical mixing rates in a typical area river, the Loosahatchie River, over an extent that is believed to have an outcrop of the Memphis Sand unit. The Memphis Sand is the major water bearing aquifer that the city of Memphis uses for its water supply. Samples will be taken beginning upstream and moving progressively downstream to the end of the Memphis Sands Outcrop. The initial samples will be from areas before the Memphis Sand Outcrop. Water samples from the Memphis Sand aquifer itself will also be analyzed. I will then monitor the increase or decrease of several anions, pH, and Temperature in each of the stream water samples. I will then run a model to determine the aquifer input amounts of these variables to reach the measured concentrations and temperatures. Data will be obtained for this project using USGS data recorded since 1975 to present for the river and aquifer properties. Modeling for the project will be done in Visual Python.
Procedure: Memphis Sands Aquifer water samples that have been analyzed by the USGS will be analyzed. Sample wells near the Loosahatchie river section in question will be chosen preferentially to those further away. It may be possible that those wells nearest the area have not been analyzed for certain anions or physical properties. In this case, further well samples may be used. Well sample water will be checked for chloride and phosphate, as well as, pH and temperature. Values over a 5 year period will then be averaged and used as the input values from the aquifer. Loosahatchie values will also then be obtained from the USGS and also averaged over the same time period, with the exception of temperature. Surface water temperature varies greatly with the current climate making averaging difficult and misleading. If temperature readings for the river are only taken once a year, at varying points in the year, the average would be too close to ground water temperature. We will hence limit the river temperature readings to a particular point in the year of maximum high or low. This should reveal the sharpest gradient as 58 degree F groundwater is entered into the 40 degree F or 80 degree F river system. The model for the system will be done using Visual Python. Using existing DEM data for the River section in question, the area will be digitally mapped with special designation for the river position. Suspected aquifer outcrop areas will be outlined but not entered into the data analysis. The point of the project is to determine if these boundaries are valid. The Aquifer will be set to discharge a certain amount into the stream with the tested USGS values. The stream will then be set to a known flow rate with the tested USGS values as data points along the way. As a section of water moves along the river, at each data point(location where the USGS took samples) the program will analyze the amount of groundwater necessary to reach those tested river concentrations. In this manner, the program will be able to determine the groundwater discharge amount for each section of river. We can then compare this data to existing theoretical discharge amounts.
Expected Outcome: I believe that there will be a steady decrease in anion concentration due to dilution by incoming water with relatively low levels of these anions. I believe overall temperature will steadily decrease over the outcrop region due to the incoming groundwater which has a constant temperature of 58 degrees F. The pH should be more oxidizing if the river trends are similar to other documented rivers along groundwater discharge areas.
Possible Problems: The river sample temperature may be inaccurate. If the person taking the sample happens to check in an area with a high discharge, the reading may be artificially low and not representative of the entire width of the river. The depth of the temperature sample may also be a factor. It is also possible that along the section, other streams may enter into the river, adding their component concentrations and throwing off the program. Drainage ditches and other human influence may also influence results.
