Geology Reports⌕ Search

Geology topics

Research about Tennessee

Source-linked reports with geographic coverage including Tennessee.

At least 181 records · Page 10Linked to original sources
USGS1994

Water resources publications of the U.S. Geological Survey for Tennessee, 1987-1993

This report presents an updated bibliography of water-resources related reports authored or co-authored by personnel of the U.S. Geological Survey, Water Resources Division, Tennessee District The bibliography lists 102 reports published by the U.S. Geological Survey during the period 1987 through 1993. Articles, papers, and abstracts published by non-U.S. Geological Survey sources for this same period also are listed. The report augments a previous bibliography for the years 1906-1987.

Tennessee↗
USGS1994

Rainfall, streamflow, and water-quality data for five small watersheds, Nashville, Tennessee, 1990-92

Rainfall, streamflow, and water-quality data were collected during storm conditions at five urban watersheds in Nashville, Tennessee. These data can be used to build a database for developing predictive models of the relations between stormwater quality and land use, storm characteristics, and seasonal variations. The primary land use and mix of land uses was different for each watershed. Stormwater samples were collected during three storms at each watershed and analyzed for selected volatile, acidic and base/neutral organic compounds; organic pesticides; trace metals; conventional pollutants; and several physical properties. Storm loads were computed for all constituents and properties with event mean concentration above the minimum reporting level. None of the samples contained acidic organic compounds at concentrations above the minimum reporting levels. Several constituents in each of the other categories, however, were present at concentrations above this level. For 21 of these, water-quality criteria have been promulgated by the State of Tennessee. For only 8 of the 21 did the value exceed the most restrictive of the criteria: pyrene, dieldrin, and mercury concentrations and counts of fecal * coliform exceeded the criteria for recreational use, copper and zinc concentrations and p value exceeded the criteria for fish and aquatic life, and lead concentrations exceeded for domestic supply.

Tennessee↗
USGS1994

Estimated use of water in Tennessee, 1990

Water withdrawals in Tennessee in 1990 were estimated to average 9,210 million gallons per day (Mgal/d) for offstream uses--a 9-percent increase from the 1985 estimate. Average per capita water use for all offstream uses was 1,890 gallons per day. Public-supply with- drawals (712 Mgal/d) represented a 14-percent increase from 1985 withdrawals. Self-supplied withdrawals during 1990 changed since 1985 as follows: domestic (59 Mgal/d), 16-percent decrease; commercial (55 Mgal/d), 1,000-percent increase; industrial (882 Mgal/d), 590-percent increase; and thermoelectric (7,320 Mgal/d), 21-percent increase. Total surface-water with- drawals in 1990 averaged 8,760 Mgal/d, which represents a 9-percent increase since 1985. Total ground-water withdrawals averaged 451 Mgal/d, which represents a 2-percent increase since 1985. Ninety-seven percent of the water used (8,950 Mgal/d) was returned to streams.

Tennessee↗
USGS1993

Logs of exploratory trenches through liquefaction features on late Quaternary terraces in the Obion River Valley, northwestern Tennessee

From December 1811 to February 1812, four large earthquakes (m b ≥7.0) occurred in the New Madrid (Missouri) Seismic Zone (NMSZ). These have been the largest historical earthquakes in eastern North America. Although this area has been the focus of considerable seismological research, estimates of the repeat time of large-magnitude seismic events remain poorly constrained. Past estimates were primarily based on earthquake-frequency statistics and on paleoseismology studies. Johnston and Nava (1985) compiled historical seismicity data covering about 180 years and instrumental data covering 10 years, and they concluded that the repeat time for large-magnitude events (m b ≥7.0) is between 500 and 1,100 yrs. However, this estimate is based on assumptions that the data set is representative of the seismicity of the region over the past 1,000 yrs, and that the relation between earthquake frequency and magnitude is constant (Johnston and Nava, 1985). Because these assumptions cannot be verified, this estimated recurrence interval of 550-1,100 hrs must be considered tentative (S. G. Wesnousky and L. M. Leffler, written commun., 1991). Investigation of exploratory trenches across the Reelfoot scarp in northwestern Tennessee documented the only unequivocal Holocene surface faulting in the upper Mississippi embayment (Russ and others, 1978; Russ, 1979). Fluvial sediment younger than about 2,250 yrs old is faulted, and the net vertical displacement is more than 3 m. Stratigraphic relations indicate at least two episodes of faulting occurred between about 2,250 yr B.P. and the 1811-12 events to estimate an average recurrence interval of less than 600 yrs for large-magnitude earthquakes in the NMSZ. However, inasmuch as Russ (1970) found no evidence for any historical offset on the Reelfoot scarp, the relation between the Reelfoot scarp and large paleoeartchquakes in the NMSZ has not been clearly established. The development of widespread liquefaction features suring the 1811-12 earthquake series (Obermeier, 1989, Obermeier and others, 1990) and the probably development of similar features during previous large-magnitude seismic events (m b ≥6.2, Nuttli, 1982) have been the basis for several attempts to document the history of paleoliquefaction. Haller and Crone (1986) found evidence of only one episode of sand-blow development in exploratory trenches in late Pleistocene alluvium in eastern Arkansas and concluded that this liquefaction event was probably associated with the 1811-12 earthquake series. Saucier (1989) reported evidence of three liquefaction events in the past approximately 1,000 yrs in an exploratory trench in eastern Arkansas. On the basis of the apparent absence of post-depositional erosion separating the three sand-blow deposits, Saucier (1989) concluded that they formed in a relatively short period of time, probably during the 1811-12 earthquake series. Similarly, Schweig and Marple (1991) found evidence of only recent (probably 1811-12) liquefaction in exploratory trenched on late Wisconsin braided-stream deposits in southeastern Missouri. Leffler and Wesnousky (1991) and Wesnousky and Leffler (written commun., 1991) examined tens of kilometers of recently excavated drainage ditches in late Wisconsin braided-stream deposits in eastern Arkansas and found no evidence for prehistorical liquefaction events during the last 10,000 yrs. In contrast, Saucier (1991) estimated an average recurrence interval about 470 yrs on the basis of historical ages of liquefaction in the NMSZ. The lack of similar evidence from other sites implies a prehistorical liquefaction-producing seismic event in southeastern Missouri that was considerably smaller than the 1811-12 earthquake series. The apparent absence of paleoliquefaction features in late Wisconsin fluvial deposits in the zone of most intense 1811-12 liquefaction indicates that the repeat time of large (m b ≥7.0) seismic events in the NMSZ is at least 10,000 yrs (Saucier, 1991; Wesnousky and Leffler, written commun., 1991). The present study was undertaken to verify this conclusion by documenting the record of liquefaction in late Wisconsin fluvial deposits along the Obion River, in northwestern Tennessee, This region was identified by Obermeier (1989) as an area deserving further study because of its proximity to the NMSZ and to areas of historical liquefaction.

Tennessee↗
USGS1993

Construction, lithologic, and hydrologic data for test wells in the Cedar Grove area, Carroll County, Tennessee

Four test wells were drilled near Cedar Grove in Carroll County, Tennessee, in 1991 to obtain geologic and hydrologic information about the post-Cretaceous strata in the study area. Samples of cuttings and geophysical logs were used to determine the lithology and stratigraphy at the drilling sites. Specific-capacity tests and water-quality analyses were conducted at two test wells completed in the Memphis Sand. Yields of the two test wells were 275 gallons per minute and greater than 350 gallons per minute. The specific capacities for the two wells equalled 17.8 and 10.0 gallons per minute per foot of drawdown, respectively.

Tennessee↗
USGS1993

Hydrologic and hydraulic analyses at Akin Branch and Cayce Valley Branch, Columbia, Tennessee

The U.S. Geological Survey, in cooperation with the City of Columbia, Tennessee, conducted hydrologic and hydraulic analyses at Akin Branch and Cayce Valley Branch in the Little Bigby Creek watershed, Columbia, Tennessee, from 1990 through 1991. Results of the analyses can be used by city planners in the development of plans to replace several deteriorating and inadequate drainage structures. Akin Branch and Cayce Valley Branch drain small watersheds of 1.69 and 1.04 square miles, respectively. Flood discharges for 5-, 10-, and 25-year recurrence-interval storm events were calculated at the stream mouths using flood-frequency relations developed for use at small urban streams in Tennessee. For each stream, flood discharges at locations upstream from the mouth were calculated by subdividing the watershed and assigning a percentage of the discharge at the mouth, based on drainage area, to each subarea. Flood profiles for the selected recurrence-interval flood discharges were simulated for Akin Branch and Cayce Valley Branch for existing conditions and conditions that might exist if drainage improvements such as larger culverts and bridges and channel improvements are constructed. The results of the simulations were used to predict changes in flood elevations that might result from such drainage improvements. Analyses indicate that reductions in existing flood elevations of as much as 2.1 feet for the 5-year flood at some sites on Akin Branch and as much as 3.8 feet for the 5-year flood at some sites on Cayce Valley Branch might be expected with the drainage improvements.

Tennessee↗
USGS1993

Water resources data, Tennessee, water year 1992

Water resources data for the 1992 water year for Tennessee consists of records of stage, discharge, and water quality of streams and springs; stage, contents, and water quality of lakes and reservoirs; water levels and water quality of wells; and quantity and quality of precipitation. This report contains discharge records for 76 gaging stations; elevation and contents for 27 lakes and reservoirs; water quality for 17 stations and 10 wells; water levels for 22 observation wells; and 1 precipitation station. Also included are 90 crest-stage partial-record stations. Additional water data were collected at various stream sites not involved in the systematic data collection program and are published as miscellaneous measurements and analyses. These data represent that part of the National Water Data System operated by the U.S. Geological Survey and cooperating State and Federal agencies in Tennessee.

Tennessee↗
USGS1993

Ground-water hydrology of the lower Wolftever Creek basin, with emphasis on the Carson Spring area, Hamilton County, Tennessee

An investigation of the ground-water-flow system that supplies Carson Spring and the surrounding lower Wolftever Creek basin northeast of Chattanooga, Tennessee, was conducted from September 1986 through December 1989. About two-thirds of the lower basin is underlain by the Chepultepec Dolomite of Ordovician age. Test drilling within a few miles of the spring showed that numerous solution cavities have developed in this formation; many are partly or completely plugged with cherty gravels and mud. In the recharge area to the spring, the formation can provide yields of 100 to perhaps 600 gallons of water per minute to bedrock wells. A well that penetrated a well-integrated cavity system underlying Carson Spring was tested at 2,000 gallons per minute. From May 1987 through December 1989, mean daily withdrawals from four wells at Carson Spring ranged from 4.78 to 5.83 cubic feet per second; mean daily spring discharge, which includes withdrawals, ranged from 5.53 to 5.79 cubic feet per second. For a 16-month drought period during 1987 and 1988, withdrawals from these wells exceeded natural spring discharge, and demonstrates that for a period of many consecutive months, the aquifer supplying the spring is capable of yielding more water than the spring would have discharged under natural conditions. Although the lower basin encompasses 17 square miles, the Carson Spring recharge area probably is not greater than 9 square miles. Most water not captured by cavities supplying the spring is discharged to Wolftever Creek. In the lower basin, the rate of ground-water discharge to the creek is about twice the average rate of discharge (0.25 cubic foot per second per square mile of drainage area) to area streams. Principal constituents in ground water in the lower basin are calcium and bicarbonate, or calcium, magnesium, and bicarbonate. Specific conductance commonly ranges from 100 to 700 microsiemens per centimeter, and pH usually ranges from about 7 to 8. Overall, the ground water is of good quality and suitable for most uses. Several potential sources of degradation are present and arise from industrial, municipal, and domestic activities.

Tennessee↗
USGS1993

Recent sedimentation and surface-water flow patterns on the flood plain of the North Fork Forked Deer River, Dyer County, Tennessee

Sedimentation in the 19th and 20th centuries has had a major effect on surface-water drainage conditions along a 7-mile section of the North, Fork Forked Deer River flood plain, Dyer County, Tenn. During the century prior to 1930, 5 to 12 feet of sediment were deposited over much of the flood plain, resulting in channel obstruction and widespread flooding. The estimated bankfull capacity of the natural channel before it was channelized in 19 16 was comparable to the base flow of the river during the 1980's. Ditching of the river between 191i6 and 1;9,21 was followed by reductions in sedimentation rates over parts of the flood plain. However, the effects of sedimentation have persisted. Occlusions along the natural channel of the river have divided this stream reach into a series of sloughs. These sloughs continue to fill with sediment and are surrounded by ponds that have expanded since 1941. Degradation of the North Fork Forked Deer ditch may eventually reduce ponding over much of the flood plain. Active incision of headcuts in both banks of the ditch is enhancing the drainage of widespread ponded areas. These headcuts likely will have limited effect on drainage of most tributaries. The highest recent sedimentation rates, in places more than 0.2 foot per year, are concentrated near the flood-plain margin along tributary streams. In conjunction with beaver dams and debris, ongoing sedimentation has blocked flow in several tributaries, posing a flood hazard to agricultural land near the flood-plain margin. The occluded tributaries likely will continue to overflow unless they are periodically dredged or their sediment loads are reduced.

Tennessee↗
USGS1993

Geochemistry of and radioactivity in ground water of the Highland Rim and Central Basin aquifer systems, Hickman and Maury counties, Tennessee

A reconnaissance of the geochemistry of and radioactivity in ground water from the Highland Rim and Central Basin aquifer systems in Hickman and Maury Counties, Tennessee, was conducted in 1989. Water in both aquifer systems typically is of the calcium or calcium magnesium bicarbonate type, but concentrations of calcium, magnesium, sodium, potassium, chloride, and sulfate are greater in water of the Central Basin system; differences in the concentrations are statistically significant. Dissolution of calcite, magnesium-calcite, dolomite, and gypsum are the primary geochemical processes controlling ground-water chemistry in both aquifer systems. Saturation-state calculations using the computer code WATEQF indicated that ground water from the Central Basin system is more saturated with respect to calcite, dolomite, and gypsum than water from the Highland Rim system. Geochemical environments within each aquifer system are somewhat different with respect to dissolution of magnesium-bearing minerals. Water samples from the Highland Rim system had a fairly constant calcium to magnesium molar ratio, implying congruent dissolution of magnesium-bearing minerals, whereas water samples from the Central Basin system had highly variable ratios, implying either incongruent dissolution or heterogeneity in soluble constituents of the aquifer matrix. Concentrations of radionuclides in water were low and not greatly different between aquifer systems. Median gross alpha activities were 0.54 picocuries per liter in water from each system; median gross beta activities were 1.1 and 2.3 picocuries per liter in water from the Highland Rim and Central Basin systems, respectively. Radon-222 concentrations were 559 and 422 picocuries per liter, respectively. Concentrations of gross alpha and radium in all samples were substantially less than Tennessee’s maximum permissible levels for community water-supply systems. The data indicated no relations between concentrations of dissolved radionuclides (uranium, radium-226, radium-228, radon-222, gross alpha, and gross beta) and any key indicators of water chemistry, except in water from the Highland Rim system, in which radon-222 was moderately related to pH and weakly related to dissolved magnesium. The only relation among radiochemical constituents indicated by the data was between radium-226 and gross alpha activity; this relation was indicated for water from both aquifer systems.

Tennessee↗
USGS1993

Hydrology of the Jackson, Tennessee, area and delineation of areas contributing ground water to the Jackson well fields

A comprehensive hydrologic investigation of the Jackson area in Madison County, Tennessee, was conducted to provide information for the development of a wellhead-protection program for two municipal well fields. The136-square-mile study area is between the Middle Fork Forked Deer and South Fork Forked Deer Rivers and includes the city of Jackson. The formations that underlie and crop out in the study area, in descending order, are the Memphis Sand, Fort Pillow Sand, and Porters Creek Clay. The saturated thickness of the Memphis Sand ranges from 0 to 270 feet; the Fort Pillow Sand, from 0 to 180 feet. The Porters Creek Clay, which ranges from 130 to 320 feet thick, separates a deeper formation, the McNairy Sand, from the shallower units. Estimates by other investigators of hydraulic conductivity for the Memphis Sand range from 80 to 202 feet per day. Estimates of transmissivity of the Memphis Sand range from 2,700 to 33,000 feet squared per day. Estimates of hydraulic conductivity for the Fort Pillow Sand range from 68 to 167 feet per day, and estimates of transmissivity of that unit range from 6,700 to 10,050 feet squared per day. A finite-difference, ground-water flow model was calibrated to steady-state hydrologic conditions of April 1989, and was used to simulate hypothetical pumping plans for the North and South Well Fields. The aquifers were represented as three layers in the model to simulate the ground-water flow system. Layer 1 is the saturated part of the Memphis Sand; layer 2 is the upper half of the Fort Pillow Sand; and layer 3 is the lower half of the Fort Pillow Sand. The steady-state water budget of the simulated system showed that more than half of the inflow to the ground-water system is underflow from the model boundaries. Most of this inflow is discharged as seepage to the rivers and to pumping wells. Slightly less than half of the inflow is from areal recharge and recharge from streams. About 75 percent of the discharge from the system is into the streams, lakes, and out of the model area through a small quantity of ground-water underflow. The remaining 25 percent is discharge to pumping wells. The calibrated model was modified to simulate the effects on the ground-water system of three hypothetical pumping plans that increased pumping from the North Well Field to up to 20 million gallons per day, and from the South Well Field, to up to 15 million gallons per day. Maximum drawdown resulting from the 20 million-gallons-per-day rate of simulated pumping was 44.7 feet in a node containing a pumping well, and maximum drawdown over an extended area was about 38 feet. Up to 34 percent of ground-water seepage to streams in the calibrated model was intercepted by pumping in the simulations. A maximum of 9 percent more water was induced through model boundaries. A particle-tracking program, MODPATH, was used to delineate areas contributing water to the North and South Well Fields for the calibrated model and the three pumping simulations, and to estimate distances for different times-of-travel to the wells. The size of the area contributing water to the North Well Field, defined by the 5-year time-of-travel capture zone, is about 0.8 by 1.8 miles for the calibrated model and pumping plan 1. The size of the area for pumping plan 2 is 1.1 by 2.0 miles and, for pumping plan 3, 1.6 by 2.2 miles. The range of distance for l-year time-of-travel to individual wells is 200 to 800 feet for the calibrated model and plan 1, and 350 to 950 feet for plans 2 and 3. The size of the area contributing water to the South Well Field, defined by the 5-year time-of-travel capture zone, is about 0.8 by 1.4 miles for the calibrated model. The size of the area for pumping plans 1 and 3 is 1.6 by 2.2 miles and, for pumping plan 2, 1.1 by 1.7 miles. The range of distance for l-year time-of-travel to individual wells is 120 to 530 feet for the calibrated model, 670 to 1,300 feet for pumping plans 1 and 3, and 260 to 850 feet for pumping plan 2.

Tennessee↗
USGS1993

Water availability, use, and estimated future water demand in the upper Duck River basin, middle Tennessee

The Duck River in Tennessee supplied about 18.9 Mgal of water/d to Tullahoma, Manchester, Lewisburg, Columbia, and other cities. Municipal water use increased to 20.9 Mgal/d in 1990; projections indicate increases in demand for the next 25 yr. Socioeconomic and water use data from the basin for 1989 were used to calibrate the water use models within the Institute for Water Resources Municipal and Industrial Needs (IWR-MAIN) System. The models were used to estimate future water use demand in the basin for the years 1995, 2000, and 2015. Projections showed demands of about 24.3 Mgal/d in 1995; 28.3 Mgal/d in 2000; and 39.0 Mgal/d in 2015. Increases in withdrawals from the Duck River downstream from Shelbyville could reduce the minimum flow at Columbia from 119 to 83.8 cu feet/s. The study also included an overview of the potential for developing groundwater resources in the area. Statistical analyses of yields to 5,938 wells showed that the highest yields are in Coffee County, but 75 percent of the wells in Coffee County produced less than 30 gal/m. However, measurements of streamflow losses along tributaries to the Duck River suggest that the potential for development of groundwater does exist at specific sites.

Tennessee↗
USGS1993

Evaluation of subsurface exploration, sampling, and water-quality-analysis methods at an abandoned wood-preserving plant site at Jackson, Tennessee

Direct Push Technology (DPT) and a modified-auger method of sampling were used at an abandoned wood-preserving plant site at Jackson, Tennessee, to collect lithologic data and ground-water samples in an area known to be affected by a subsurface creosote plume. The groundwater samples were analyzed using (1) gas chromatography with photo-ionization detection (GS/PID), (2) high- performance liquid chromatography (HPLC), (3) colonmetric phenol analysis, and (4) toxicity bioassay. DPT piezocone and cone-penetrometer-type tools provided lithologic data and ground-water samples at two onsite stations to a depth of refusal of about 35 feet below land surface. With the assistance of an auger rig, this depth was extended to about 65 feet by pushing the tools in advance of the augers. Following the DPT work, a modified-auger method was tested by the USGS. This method left doubt as to the integrity of the samples collected once zones of contamination were penetrated. GC/PID and HPLC methods of water-quality analysis provided the most data concerning contaminants in the ground-water and proved to be the most effective in creosote plume detection. Analyses from these methods showed that the highest concentrations of contaminants were detected at depths less than about 35 feet below land surface. Phenol analyses provided data supplemental to the HPLC analyses. Bioassay data indicated that toxicity associated with the plume extended to depths of about 55 feet below land surface.

Tennessee↗
USGS1993

Preliminary results of a helicopter electromagnetic and magnetic survey of the Oak Ridge Reservation, Tennessee for environmental and geologic site characterization

The 35,252 -acre Oak Ridge Reservation (ORR), in the western portion of the Appalachian Valley and Ridge province in Tennessee, has been a nuclear production and development facility for 50 years. Contaminants in the many waste sites on the ORR include heavy radioactive isotopes as well as many organic and inorganic compounds. The locations, geometry, and contents of many of these waste sites are reasonably well known, while others are poorly known, and some may be unknown. To better characterize the known sites and locate and characterize additional environmentally hazardous sites, a two-phase aerial survey of the ORR was begun in April, 1992. Phase I, which began in April, 1992, consisted of aerial radiation, multispectral scanner, and photographic surveys. Phase II, which began in November, 1992 and is described in this presentation, consisted of a helicopter electromagnetic (HEM), magnetic, and radiation survey. Targets of the survey were both man-made (drums, trench boundaries, burn pits, well heads) and geologic (fractures, faults, karst features, geologic contacts). The Phase II survey has three components: testing, reconnaissance, and high-resolution data acquisition. To date, the testing and reconnaissance data acquisition have been completed, and part of the data have been processed. They indicate that: 1) magnetic and HEM data are complementary, and do not always highlight the same anomaly; 2) under favorable circumstances, helicopter magnetometer systems are capable of detecting groups of 4 or more 55-gallon drums at detector altitudes of 15 m or less, 3) HEM data provide data which compare favorably with surface data collected over burial trenches, 4) well casings seem to be related to magnetic monopole anomalies, as would be expected, 5) Changes in EM and magnetic anomaly character are related to lithologic changes and might be used to track contacts between known outcrops.

Tennessee↗
USGS1992

Reconnaissance investigation of volatile and semivolatile organic compounds in the Memphis Aquifer at Alamo, Crockett County, Tennessee

Samples of ground water and soil gas were analyzed to study the occurrence of volatile and semivolatile organic compounds in the Memphis aquifer at Alamo in western Tennessee in 1989. At Alamo, the aquifer is locally unconfined. Four wells screened in the Memphis aquifer provided Alamo with 0.3 million gallons of water per day. Trichloroethylene (TCE), dichloroethylene, trichloroethane, and tetrachloroethylene were detected in water samples from two of the wells. In September 1989, the TCE concentration in a sample from well 1 was 45 micrograms per liter (mg/L); Tennessee’s maximum contaminant level for TCE in drinking water is 5 mg/L Concentrations of TCE in water from this well ranged from 40 to 113 mg/L during I988 and 1989. TCE concentration in water collected from well 2 in September 1989 was 0.7 mg/L During I988 and 1989, TCE concentrations in this well ranged from less than 0.5 to 5.1 mg/L None of the semivolatile organic compounds on the U.S. Environmental Protection Agency’s priority-pollutant list were detected in water from well 1. Soil gas was sampled at a depth of 3.5 feet below land surface in areas of suspected ground-water contamination. Analyses by gas chromatography indicated the presence of TCE in soils about 230 feet east of well 1 in the area of a former industrial site where solvents were handled. TCE concentrations in the soil gas of this area ranged from 0.2 to 30 mg/L TCE was not detected in soil gas near any of the wells. Depth to water at the wells ranged from 39 to 49 feet. The regional direction of ground-water flow is to the west-southwest, which would cause contaminants dissolved in ground water below the former industrial-site area to be transported toward the public-supply wells. Probable reasons contributing to the lack of TCE detection in soil gas at wells 1 and 2 are the relatively low concentrations of TCE in ground water at the wells and the vertical distance between sampling points and the water table.

Tennessee↗
USGS1992

Geomorphic and vegetative recovery processes along modified stream channels of West Tennessee

Hundreds of miles of streams in West Tennessee have been channelized or otherwise modified since the turn of century. After all or parts of a stream are straightened, dredged, or cleared, systematic hydrologic, geomorphic, and ecologic processes collectively begin to reduce energy conditions towards the premodified state. One hundred and five sites along 15 streams were studied in the Obion, Forked Deer, Hatchie, and Wolf River basins. All studied streams, except the Hatchie River, have had major channel modification along all or parts of their courses. Bank material shear-strength properties were determined through drained borehole-shear testing (168 tests) and used to interpret present critical bank conditions and factors of safety, and to estimate future channel-bank stability. Mean values of cohesive strength and angle of internal friction were 1.26 pounds per square inch and 30.1 degrees, respectively. Dendrogeomorphic analyses were made using botanical evidence of channel-bank failures to determine rates of channel widening; buried riparian stems were analyzed to determine rates of bank accretion. Channel bed-level changes through time and space were represented by a power equation. Plant ecological analyses were made to infer relative bank stability, to identify indicator species of the stage of bank recovery, and to determine patterns of vegetation development through the course of channel evolution. Quantitative data on morphologic changes were used with previously developed six-stage models of channel evolution and bank-slope development to estimate trends of geomorphic and ecologic processes and forms through time. Immediately after channel modifications, a 10- to 1%yearperiod of channel-bed degradation ensues at and upstream from the most recent modifications (area of maximum disturbance). Channel-bed lowering by &gradation was as much as 20 feet along some stream reaches. Downstream from the area of maximum disturbance, the bed was aggraded by the deposition of sediment supplied by knickpoint migration upstream; aggradation also occurred in initially degraded sites with time. Additionally, if degradation caused an increase in bank height beyond the critical limits of the bank material, a period of channel widening by mass wasting followed. Degradation knickpoints migrated upstream at rates greater than 1 mile per year; the rates attenuated with distance above the area of maximum disturbance. Channel widening rates of up to 16 feet per year were documented along some severely degraded reaches. Planar failures were generally more frequent but rotational failures dominated the most rapidly widening reaches. Total volumes of bank erosion may represent 75percent or more of the total material eroded from the channel, but this material generally exits the drainage basin. Mean factors of safety vary with the stage of channel evolution with the lowest values for planar and rotational failures occurring during the threshold stage (stage IV) 1.00 and 1.15, respectively. As channel gradients decrease, degradation ceases and then a period of “secondary aggradation ” (at lesser rates than degradation) and bank accretion begins that may fill the channel to near floodplain level. This shift@ in process represents an oscillation in channel bed-level adjustment. Streams in basins underlain by loess may require an order of magnitude more time than sand-bed streams to stabilize due to a lack of coarse-grained material (sand) for aggradation. A systematic progression of riparian species that reflects the six-stage model of channel evolution has been identified. This progression can be used to infer ambient channel stability and hydrogeomorphic conditions. Woody vegetation establishes on low- and mid-bank surfaces (the slough line, initially) at about the same time that bank accretion begins. This slough line forms at a mean temporary stability angle of 24 degrees and expands upslope with time by the accretion of sediments. Species involved in this initial revegetation are hardy, fast growing, and can tolerate moderate amounts of slope instability and sedimentation; these species include river birch, black willow, boxelder, and silver maple. Vegetation appears to enhance bank stability, and with increasing stability, species such as bald cypress, tupelo gum, and various hydric oaks, which are more characteristic of stable, premodified riparian settings, begin to establish. Detrended-correspondence analysis indicated species assemblages associated with the six stages of channel evolution and bank-slope development. Ordination of site variables based on species data such as channel widening, bank accretion, and woody vegetative cover also reflects the temporal changes identifies by the models. Long-term channel geometry was estimated from a quantitative model of bed-level change, and from documented trends in channel widening. An idealized stable channel of a major sand-bed stream may have a width/depth ratio near 10 and bank slopes of about 24 degrees. This stable channel will ultimately undergo the development of point-bars and incipient meanders, characteristic of unmodified streams.

Tennessee↗