Rainfall and Water-Level Data for a Wetland Area near Millington, Shelby County, Tennessee, October 1996 through September 1997

Rainfall amounts and water levels at a degraded wetland area near Millington, Shelby County, Tennessee, were collected to assist the Tennessee Department of Transportation with a program designed to restore the wetland to a more natural condition. The site is located along a channelized reach of Big Creek Drainage Canal, east of State Route 240, and near the southeastern boundary of the Naval Support Activity Memphis, Millington. Rainfall amounts were recorded at 5-minute intervals using a tipping-bucket rain gage from October 1, 1996 through September 30, 1997. Total rainfall for this period was 70.16 inches. In general, water levels at the wetland were above or near the ground surface during the 6-month period from the first of January through June 1997. For the remainder of the year, water levels generally subsided to several feet below land surface. However, some locations within the wetland were wet or highly saturated year round.

In recent years, restoring and preserving wetlands has become an important environmental initiative. Wetlands perform many vital functions in maintaining the ecological integrity of regional environments. Wetlands provide storage and filtration of surface water, diverse habitats for plants and animals, corridors for the movements of animals and dissemination of plants, and a supply of nutrients to nearby aquatic environments (Light and others, 1993). Wetlands have been defined as "those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions" (Sipple, 1987).

"No net loss of wetlands" (Lyon, 1993) is the objective of Section 404 of the Clean Water Act (U.S. Congress, 1977) enacted by the Federal government. In certain instances, the construction of buildings, roads, and other manmade structures may disrupt natural wetlands and their functions. Therefore, the protection, restoration, or creation of wetlands that have been disturbed or destroyed is necessary.

In 1993, the U.S. Geological Survey (USGS), in cooperation with the Tennessee Department of Transportation (TDOT), began monitoring a degraded wetland area near Millington, Shelby County, Tennessee, to define land surface inundation and saturation conditions prior to the implementation of a plan to restore the wetland area to a more natural condition. The site is located along a channelized reach of Big Creek, east of State Route 240, and near the southeastern boundary of the Naval Support Activity Memphis, Millington (fig. 1).

The purpose of this report is to summarize rainfall and water-level data recorded at a wetland area near Millington, Tennessee, during the period October 1, 1996 through September 30, 1997. This report supplements information recorded at this site from June 1, 1993 through June 30, 1994 (Robinson and others, 1996); July 1, 1994 through September 30, 1995 (Robinson and Diehl, 1996); and October 1, 1995 through September 30, 1996 (Knight, 1997).

The wetland study area is located along a channelized reach of Big Creek Drainage Canal near Millington in Shelby County, Tennessee. The site is approximately 370 acres of flood plain adjacent to a 6,200-foot reach of Big Creek Drainage Canal. The site also receives surface runoff from about 400 acres of surrounding land. Big Creek Drainage Canal flows to the southwest and empties into the Loosahatchie River at a point approximately 10 miles upstream from the Mississippi River.

Soils in this region of Tennessee include the somewhat poorly drained Calloway silt loam and Falaya silt loam, and the poorly drained Waverly silt loam and Henry silt loam [Sease and others, 1970; J.C. Jenkins, Soil Conservation Service (now Natural Resources Conservation Service), oral commun., 1993]. The average growing season in the area, defined as the average period between the last spring frost and the first autumn frost, is from March 15 to November 12 (M.E. Zeman, Natural Resources Conservation Service, written commun., 1995). In the past, the wetland area had been drained and was used for crop farming.

Rainfall amounts were measured using a tipping-bucket rain gage located at well W2-1 (fig. 1) and were recorded at 5-minute intervals from October 1, 1996 through September 30, 1997. Daily rainfall amounts for this period are provided in the Supplemental Data section of this report. The total rainfall amount recorded by the rain gage from October 1, 1996 through September 30, 1997 was 70.16 inches, 47 percent more than during the previous year. The average rainfall for this area is 49.73 inches (Sease and others, 1970).

Water levels were recorded at 1-hour intervals at thirteen 8-inch diameter wells. The wells used to monitor water levels at the site are typically about 2 feet deep. The methods used for well construction are described in a report by Robinson and others (1996). Water levels in the study area were generally 1.5 feet or more below land surface during October 1996 and from July through September 1997. Water levels were generally within 1.5 feet below land surface during November and December 1996 and from January through April 1997. Plots of hourly water levels recorded at the wells can be found in figures 2, 3, 4, 5, and 6.

The percentage of the time each well was inundated and within 1.5 feet below land surface was based on mean daily water level and is presented in table 1. These conditions were determined for both the dry season, summer/fall, and wet season, winter/spring.

Water levels recorded at 13 wells at the wetland indicate that land surface inundation and saturation conditions varied during the year. During the winter/spring season, water levels in 2 of the 13 wells (W2-2 and W2-5) were within 1.5 feet below land surface less than 50 percent of the time. Water levels at 7 of the 13 wells (W1-1, W1-2, W1-3, W1-5, W2-1, W2-4, and W2-6) were within 1.5 feet below land surface between 50 and 75 percent of the time. Water levels in four wells (W1-4, W2-3,W3-2, and W3-3) were within 1.5 feet below land surface more than 75 percent of the time during the winter/spring season. During the summer/fall season, the percentage of time that water levels were within 1.5 feet below land surface was generally less than 50 percent, with the exception of well W3-3, which was within 1.5 feet below land surface 86 percent of the time.

Water levels were above land surface at five wells during the winter/spring months and at three wells during the summer/fall months. Well W1-2 was inundated 50 percent of the time and W2-1 was inundated 1 percent of the time. Well W2-6 was inundated 37 percent of the time, W3-2 was inundated less than 1 percent of the time, and W3-3 was inundated 93 percent of the time. The three wells that were inundated during the summer/fall months were W1-2, inundated 30 percent of the time; W1-4, inundated less than 1 percent of the time; and W3-3, inundated 73 percent of the time.

Water levels at 11 of the 13 sites were within 1.5 feet below land surface for 2 weeks or longer during the local growing season (March 15 through November 12). Wetland conditions may occur when water is within 0.5 to 1.5 feet below land surface for 2 weeks or longer during the growing season. Specific depth depends upon the soil characteristics. Water levels at two wells, W2-1 and W2-2, were within 1.5 feet below land surface very few days during the growing season.

This report presents rainfall amounts and water levels recorded at a degraded wetland site near Millington, Tennessee, during the period from October 1, 1996 through September 30, 1997. These data were collected by the U.S. Geological Survey to assist the Tennessee Department of Transportation with the implementation of a plan to restore the wetland to a more natural condition. In the past, the wetland had been cleared, drained, and used to farm crops.

Rainfall information was collected in the study area from October 1, 1996 through September 30, 1997. Rainfall totaled 70.16 inches, 47 percent more than during the previous year.

Water levels recorded at 13 wells at the wetland indicate that land surface inundation and saturation conditions varied during the year. During the summer/fall season, 11 of the 13 wells had mean daily water levels that were within 1.5 feet below land surface. The percentages of time that these 11 wells were in this range varied from 3 to 86 percent. Well W3-3 was the only well with water-levels within 1.5 feet below land surface for more than 50 percent of the time during this season. All 13 wells had water-levels within 1.5 feet below land surface during the winter/spring season with only two wells, W2-2 and W2-5, having water-levels within 1.5 feet below land surface less than 50 percent. The winter/spring season provided the highest periods of inundation. Of the 13 wells, 5 wells were inundated from about 1 to 93 percent of the time. Wells W1-2, W1-4, and W3-3 were inundated during the summer/fall months.