Geology topics

T.H. Diehl

Publications and source records attributed to T.H. Diehl.

6 recordsLinked to original sources

USGS2009

River restoration strategies in channelized, low-gradient landscapes of West Tennessee, USA

West Tennessee has a complex history of watershed disturbance, including agricultural erosion, channelization, accelerated valley sedimentation, and the removal and reestablishment of beaver. Watershed management has evolved from fl oodplain drainage via pervasive channelization to include local drainage canal maintenance and local river restoration. Many unmaintained canals are undergoing excessive aggradation and complex channel evolution driven by upland erosion and low valley gradient. The locus of aggradation in fully occluded canals (valley plugs) moves up-valley as sediment continues to accumulate in the backwater behind the plug. Valley plugs that cause canal avulsion can lead to redevelopment of meandering channels in less disturbed areas of the fl oodplain, in a process of passive self-restoration. Some valley plugs have brought restored fl oodplain function, reoccupation of extant historic river channels, and formation of a "sediment shadow" that protects downstream reaches from excess sedimentation. Despite the presence of numerous opportunities, there is presently no mechanism for including valley plugs in mitigation projects. In 1997 a survey of 14 reference reach cross sections documented relations between drainage area and bankfull geometry of relatively unmodified streams in West Tennessee. Reassessment of seven of those sites in 2007 showed that one had been dammed by beaver and that two sites could not be analyzed further because of signifi cant vertical or lateral instability. In contrast to other regions of North America, the results suggest that stream channels in this region fl ood more frequently than once each year, and can remain out of banks for several weeks each year. ?? 2009 Geological Society of America.

Special Paper of the Geological Society of America↗

USGS1997

Preliminary conceptual models of the occurrence, fate, and transport of chlorinated solvents in karst regions of Tennessee

Published and unpublished reports and data from 22 contaminated sites in Tennessee were reviewed to develop preliminary conceptual models of the behavior of chlorinated solvents in karst aquifers. Chlorinated solvents are widely used in many industrial operations. High density and volatility, low viscosity, and solubilities that are low in absolute terms but high relative to drinkingwater standards make chlorinated solvents mobile and persistent contaminants that are difficult to find or remove when released into the groundwater system. The major obstacle to the downward migration of chlorinated solvents in the subsurface is the capillary pressure of small openings. In karst aquifers, chemical dissolution has enlarged joints, bedding planes, and other openings that transmit water. Because the resulting karst conduits are commonly too large to develop significant capillary pressures, chlorinated solvents can migrate to considerable depth in karst aquifers as dense nonaqueous-phase liquids (DNAPL's). Once chlorinated DNAPL accumulates in a karst aquifer, it becomes a source for dissolved-phase contamination of ground water. A relatively small amount of chlorinated DNAPL has the potential to contaminate ground water over a significant area for decades or longer. Conceptual models are needed to assist regulators and site managers in characterizing chlorinated-solvent contamination in karst settings and in evaluating clean-up alternatives. Five preliminary conceptual models were developed, emphasizing accumulation sites for chlorinated DNAPL in karst aquifers. The models were developed for the karst regions of Tennessee, but are intended to be transferable to similar karst settings elsewhere. The five models of DNAPL accumulation in karst settings are (1) trapping in regolith, (2) pooling at the top of bedrock, (3) pooling in bedrock diffuse-flow zones, (4) pooling in karst conduits, and (5) pooling in isolation from active ground-water flow. More than one conceptual model of DNAPL accumulation may be applicable to a given site, depending on details of the contaminant release and geologic setting. Trapping in regolith is most likely to occur where the regolith is thick and relatively impermeable with few large cracks, fissures, or macropores. Accumulation at the top of rock is favored by flat-lying strata with few fractures or karst features near the bedrock surface. Fractures or karst features near the bedrock surface encourage migration of chlorinated DNAPL into karst conduits or diffuse-flow zones in bedrock. DNAPL can migrate through one bedrock flow regime into an underlying flow regime with different characteristics or into openings that are isolated from significant ground-water flow. As a general rule, the difficulty of finding and removing DNAPL increases with depth, lateral distance from the source, and complexity of the ground-water flow system. The prospects for mitigation are generally best for DNAPL accumulation in the regolith or at the bedrock surface. However, many such accumulations are likely to be difficult to find or remove. Accumulations in bedrock diffuse-flow zones or in fractures isolated from flow may be possible to find and partially mitigate, but will likely leave significant amounts of contaminant in small fractures or as solute diffused into primary pores.

Tennessee↗

USGS1996

Hydrologic data at a wetland site, Millington, Shelby County, Tennessee, June 1993 through June 1994

Hydrologic data at a wetland site near Millington, Shelby County, Tennessee, were collected from June 1993 through June 1994. The data were collected to support the efforts of the Tennessee Department of Transportation to better understand hydrologic properties at the site prior to wetland restoration. Water levels were monitored in thirteen 8-inch- diameter wells, approximately 2 feet deep. The casing in each well was slotted and screened from land surface to a depth of about 2 feet. Water-level recorders provided continuous records of stage during periods of wetland inundation, and depth to water table during periods of noninundation. A continuous-stage recorder was installed in a pond. Precipitation data were obtained from the Naval Air Station-Memphis, Millington, Tennessee. Land surface at the wells was inundated from 0 to 56 percent of the study period. Additionally, water levels in the wells were not more than 1.5 feet below land surface for 16 to 68 percent of the study period.

Tennessee↗

USGS1996

Hydrologic data for wetland sites at Millington, Shelby County, and Huntingdon, Carroll County, Tennessee, May 1994 through September 1995

Hydrologic data at two wetland sites near Millington and Huntingdon in West Tennessee were collected to assist efforts by the Tennessee Department of Transportation to determine hydrologic conditions at the sites prior to wetland restoration. The Millington site is located along the Big Creek Drainage Canal east of State Route 240. Water levels were monitored in thirteen 8-inch-diameter wells from July 1994 through September 1995. Water-level recorders provided continuous measurement of water level during periods of wetland inundation and depth to water table during periods of noninundation. A crest-stage indicator and a continuous-stage recorder were installed to monitor surface-water fluctuation. Precipitation data were recorded to determine timing and duration of rainfall events. Land surface at the wells was inundated from 0 to 48 percent of the study period. Additionally, water levels at the wells were within 1.5 feet of the land surface from 0 to 56 percent of the study period. The Huntingdon study site is located along the Crooked Creek Drainage Canal at State Route 22. Ground-water levels were monitored in two wells (wells W-1 and W-2) with continuous water- level recorders from May 1994 through September 1995. Water levels did not rise above land surface at either well during the study. Water levels at wells W-1 and W-2 were within 1.5 feet of the land surface 46 and 50 percent of the study period, respectively. Surface-water stage was monitored at a pond on the mitigation site.

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↗

USGS1991

Wetland sedimentation and vegetation patterns near selected highway crossings in West Tennessee

Wetland sedimentation and vegetation patterns at 11 highway crossings in West Tennessee were studied from 1987 to 1989. The purpose of the study was to investigate potential adverse effects of highway crossings on wetlands. Sedimentation rates, determined from root-burial depths, were highly variable. Average rates offine-grained deposition ranged from 0.005 to 0.033 foot per year for stations in locally ponded areas and from -0.002 to 0.039 foot per year for stations in drained areas. Sedimentation rates upstream from highway crossings were not significantly different from downstream rates at 8 of the 11 study sites. Three study sites had significantly greater sedimentation rates downstream. Sand splays were observed downstream from bridges at most study sites. Vegetation patterns and tree growth appear most strongly related to hydropetiod, defined as the average length of time an area is covered by water each year. The influence of sedimentation on tree growth is difficult to separate from the influence of hydroperiod because areas with high sedimentation rates typically have long hydroperiods. Estimated hydroperiod increased no more than 1 percent because of backwater from the highway crossings at the 11 study sites, while the estimated average depth of flood-plain inundation increased by an average of 6 percent.

Tennessee↗