Geology topics

David D. Dunn

Publications and source records attributed to David D. Dunn.

4 recordsLinked to original sources

USGS2001

Indications and potential sources of change in sand transport in the Brazos River, Texas

Changes in the capacity of the Brazos River to transport sand can be identified within the context of Lane’s relation through changes in channel geometry, changes in the characteristics of suspended loads, and changes in discharge. The Brazos River channel has been undergoing continual adjustment since the 1940s. For a discharge of 5,000 cubic feet per second, the watersurface altitude has decreased 2 to 4 feet at the Hempstead and Richmond streamflow-gaging stations between 1940 and 1995. The characteristics of suspended-sediment samples at the Richmond streamflow-gaging station have changed between the periods 1969–81 and 1982– 95. The amount of sand-size sediment transported in suspension has decreased. The distribution of both daily and annual-peak discharges has changed. However, the computed annual loads of suspended sand indicate no statistically significant change in the median annual load. The transport of sand in the Brazos River depends on a complex set of factors, most of which are continually changing. Potential sources of change in sand transport in the Brazos River include the effects of reservoir construction, changes in land use, and instream sand and gravel mining. Extensive reservoir construction in the Brazos River Basin has reduced sand transport by trapping sediment and by reducing the magnitude of peak discharges. However, reductions in sand transport associated with reservoir construction apparently are compensated for by increases associated with tributary sediment inflow and localized bank erosion. The total area of harvested acres of non-hay crops in the lower Brazos River Basin during 1924–92 decreased more than 75 percent from about 32 percent to about 8 percent of the total area. Correspondingly, erosion potential has decreased substantially. Several sand and gravel mining sites are located on the Brazos River between Hempstead and Rosharon. The quantity of sediment extracted by instream sand and gravel mining operations could represent from 11 to 25 percent of the total sand transported by the Brazos River. The effects of mining on sand transport could not be quantified.

Texas↗

USGS2000

Water-quality assessment of the Trinity River Basin, Texas— Ground-water quality of the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers, February-August 1994

Ground-water samples were collected from wells in the outcrops of the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers during February-August 1994 to determine the quality of ground water in the three major aquifers in the Trinity River Basin study unit, Texas. These samples were collected and analyzed for selected properties, nutrients, major inorganic constituents, trace elements, pesticides, dissolved organic carbon, total phenols, methylene blue active substances, and volatile organic compounds as part of the U.S. Geological Survey National Water-Quality Assessment Program. Quality-control practices included the collection and analysis of blank, duplicate, and spiked samples. Samples were collected from 12 shallow wells (150 feet or less) and from 12 deep wells (greater than 150 feet) in the Trinity aquifer, 11 shallow wells and 12 deep wells in the Carrizo-Wilcox aquifer, and 14 shallow wells and 10 deep wells in the Gulf Coast aquifer. The three aquifers had similar water chemistries-calcium was the dominant cation and bicarbonate the dominant anion. Statistical tests relating well depths to concentrations of nutrients and major inorganic constituents indicated correlations between well depth and concentrations of ammonia nitrogen, nitrite plus nitrate nitrogen, bicarbonate, sodium, and dissolved solids in the Carrizo-Wilcox aquifer and between well depth and concentrations of sulfate in the Gulf Coast aquifer. The tests indicated no significant correlations for the Trinity aquifer. Concentrations of dissolved solids were larger than the secondary maximum contaminant level of 500 milligrams per liter established for drinking water by the U.S. Environmental Protection Agency in 12 wells in the Trinity aquifer, 4 wells in the Carrizo-Wilcox aquifer, and 6 wells in the Gulf Coast aquifer. Iron concentrations were larger than the secondary maximum contaminant level of 300 micrograms per liter in at least 3 samples from each aquifer, and manganese concentrations were larger than the secondary maximum contaminant level of 50 micrograms per liter in at least 2 samples from each aquifer. The pesticides atrazine, deethylatrazine, and pp'-DDE were detected in at least one sample from each aquifer. Diazinon was detected in 11 Trinity aquifer samples and 4 Carrizo-Wilcox aquifer samples. Each aquifer had one detection of a volatile organic compound-benzene in the Trinity aquifer, trichlorofluoromethane in the Carrizo-Wilcox aquifer, and trichloromethane in the Gulf Coast aquifer.

Texas↗

USGS1997

Discharge measurement in tidally affected channels during a hydrographic estuarine survey of Sabine Lake, Texas

A hydrographic survey of Sabine Lake, a broad, shallow estuary lying on the Texas-Louisiana border, was conducted in June 1996 to help address questions relating to potential environmental effects of future water demands in Texas. The use of a variety of new instruments in this study is one means by which automation is improving efficiency and effectiveness of these efforts by increasing the quality and quantity of data collected.

Texas↗

USGS1993

Plans for a sensitivity analysis of bridge-scour computations

Plans for an analysis of the sensitivity of Level 2 bridge-scour computations are described. Cross-section data from 15 bridge sites in Texas are modified to reflect four levels of field effort ranging from no field surveys to complete surveys. Data from United States Geological Survey (USGS) topographic maps will be used to supplement incomplete field surveys. The cross sections are used to compute the water-surface profile through each bridge for several T-year recurrence-interval design discharges. The effect of determining the downstream energy grade-line slope from topographic maps is investigated by systematically varying the starting slope of each profile. The water-surface profile analyses are then used to compute potential scour resulting from each of the design discharges. The planned results will be presented in the form of exceedance-probability versus scour-depth plots with the maximum and minimum scour depths at each T-year discharge presented as error bars.

Conference Paper↗