Geology topics
Jeffery W. East
Publications and source records attributed to Jeffery W. East.
U.S. Geological Survey response to flooding in Texas, May–June 2015
As a Federal science agency within the Department of the Interior, the U.S. Geological Survey (USGS) collects and disseminates streamflow stage and discharge information along with other types of water information as a major part of its Water mission area. Data collected at USGS streamflow-gaging stations (hereinafter referred to as “streamgages”) are used for a variety of purposes including flood warning, engineering design, management of water resources, and scientific research. During flood events, the need for timely, accurate, and complete streamflow data is underscored because these data are relied on by local, State, and Federal emergency management personnel for flood response purposes. For example, the National Weather Service uses the data from USGS streamgages to develop flood forecasts for specific locations on a river. Tasks that the USGS performs in response to floods include monitoring the operation of gages and responding to any interruptions in data collection, calibrating and verifying stage-discharge ratings, and documenting extreme events including peak stage and peak discharge. Frequent, severe storms during May and June 2015 caused widespread flooding in Texas. By various measures, the storms that caused the flooding were extreme and persistent. May 2015 was the wettest month on record for Texas, with a statewide average precipitation of 9.06 inches. In comparison, the long-term statewide average monthly precipitation is 3.37 inches, with the previous record average monthly precipitation reported as 6.66 inches during June 2004. The Office of the Texas State Climatologist compiled monthly precipitation amounts for 19 selected cities throughout Texas and for 1 city in Louisiana; the total monthly precipitation amounts exceeded the monthly normal precipitation for 18 of the 19 selected cities in Texas, with 5 of these cities exceeding their previous record for the month of May. The onset of abundant precipitation in May 2015 resulted in the National Weather Service flood stage being exceeded at USGS streamgages on numerous rivers. The widespread and prolonged nature of the flooding was unusual; most flood events in Texas are localized, typically affecting only one or two river basins and generally lasting only a few days. With the exception of the Rio Grande, flooding was widespread in all of the major rivers in Texas during May–June 2015.
Forecasting hurricane impact on coastal topography: Hurricane Ike
Extreme storms can have a profound impact on coastal topography and thus on ecosystems and human-built structures within coastal regions. For instance, landfalls of several recent major hurricanes have caused significant changes to the U.S. coastline, particularly along the Gulf of Mexico. Some of these hurricanes (e.g., Ivan in 2004, Katrina and Rita in 2005, and Gustav and Ike in 2008) led to shoreline position changes of about 100 meters. Sand dunes, which protect the coast from waves and surge, eroded, losing several meters of elevation in the course of a single storm. Observations during these events raise the question of how storm-related changes affect the future vulnerability of a coast.
Monitoring inland storm surge and flooding from Hurricane Ike in Texas and Louisiana, September 2008
The U.S. Geological Survey (USGS) deployed a temporary monitoring network of 117 pressure transducers (sensors) at 65 sites over an area of about 5,000 square miles to record the timing, areal extent, and magnitude of inland hurricane storm surge and coastal flooding generated by Hurricane Ike, which struck southeastern Texas and southwestern Louisiana September 12-13, 2008. Fifty-six sites were in Texas and nine were in Louisiana. Sites were categorized as surge, riverine, or beach/wave on the basis of proximity to the Gulf Coast. One-hundred five sensors from 59 sites (fig. 1) were recovered; 12 sensors from six sites either were lost during the storm or were not retrieved. All 59 sites (41 surge, 10 riverine, 8 beach/wave) had sensors to record water pressure (fig. 2), which is expressed as water level in feet above North American Vertical Datum of 1988 (NAVD88), and 46 sites had an additional sensor to record barometric pressure, expressed in pounds per square inch. Figure 3 shows an example of water level and barometric pressure over time recorded by sensors during the storm.
Water-quality, sediment-quality, stream-habitat, and biological data for Mustang Bayou near Houston, Texas, 2004-05
The U.S. Geological Survey, in cooperation with the Houston-Galveston Area Council and the Texas Commission on Environmental Quality, collected water-quality, stream-habitat, and biological data from six sites (downstream order M6-M1) primarily in Brazoria County southeast of Houston, Texas, during September 2004-August 2005 and collected bed sediment data from one site in September 2005. Water-quality data collection consisted of continuously monitored (for periods of 24 hours to several days, six times) water temperature, pH, specific conductance, and dissolved oxygen and periodically collected samples of several properties and constituents. Monitored dissolved oxygen measurements were below minimum and 24-hour criteria at all sites except M2. Nitrogen compounds, phosphorus, biochemical oxygen demand, chlorophyll-a, E. coli, chloride, sulfate, solids, suspended sediment concentration, and pesticides were assessed at all sites. Concentrations of nitrogen compounds and phosphorus did not exceed Texas State screening levels. Biochemical oxygen demand was less than 4.0 milligrams per liter at all sites except M6, where the maximum concentration was 8.1 milligrams per liter. Concentrations of chlorophyll-a were less than the State screening level at all sites except M6, where four of eight samples equaled or exceeded the screening level. Twenty of 48 samples from Mustang Bayou had E. coli densities that exceeded the State single-sample water-quality standard. Median chloride concentrations from each site were between 42.2 and 123 milligrams per liter. Fifteen pesticide compounds (six herbicides and nine insecticides) were detected in 24 water samples. The most frequently detected pesticide was atrazine, which was found in every sample. Other frequently detected pesticides were 2-chloro-4-isopropylamino-6-amino-s-triazine (CIAT), prometon, tebuthiuron, fipronil, and the pesticide degradates, fipronil sulfide and fipronil sulfone. Sediment samples were collected from the stream bottom at M1 and analyzed for concentrations of trace elements (metals), polycyclic aromatic hydrocarbons, organochlorine pesticides, and polychlorinated biphenyls. No organochlorine pesticides or polychlorinated biphenyls were detected. No concentrations of metals exceeded State screening levels. Measurable concentrations of 11 polycyclic aromatic hydrocarbon (PAH) compounds were detected, and three other PAH compounds were detected but not quantified by the laboratory. Stream habitat and aquatic biota (benthic macroinvertebrates and fish) were surveyed at each site three times during the study to evaluate aquatic life use. Characteristics of habitat measured during each survey were scored using a habitat quality index. Average aquatic-life-use scores were 'limited' for M3-M6 and 'intermediate' for M1 and M2. A total of 2,557 macroinvertebrate individuals were identified from Mustang Bayou. Benthic macroinvertebrate assemblages were scored using indexes specified by the Texas Commission on Environmental Quality. Average aquatic-life-use scores were 'limited' at M1, 'intermediate' at M3-M6, and 'high' at M2. Forty-six species of fish representing 20 families were collected from Mustang Bayou. A total of 4,115 fish were collected. Sunfish (Centrarchidae) was the most abundant family, accounting for about 28 percent. Aquatic-life-use scores at sites in Mustang Bayou were determined using the regional index of biotic integrity for ecoregion 34 and were 'high' for all sites.
Base flow (1966-2005) and streamflow gain and loss (2006) of the Brazos River, McLennan County to Fort Bend County, Texas
During 2006–07, the U.S. Geological Survey (USGS), in cooperation with the Texas Water Development Board, did a study to quantify historical (water years 1966–2005) base flow and streamflow gains and losses from two streamflow-measuring surveys (March and August 2006) in the Brazos River from McLennan County to Fort Bend County, Texas. The Brazos River is hydraulically connected to the Brazos River alluvium aquifer, which in turn is hydraulically connected to several underlying aquifers, the outcrops of which occur in laterally adjacent layers generally parallel to the coast (major aquifers, Carrizo-Wilcox and Gulf Coast, and minor aquifers, Queen City, Sparta, and Yegua-Jackson). Hydrograph separation was done using the USGS computer program Hydrograph Separation and Analysis with historical streamflow from 10 USGS gaging stations, three on the Brazos River and seven on selected tributaries to the Brazos River. Streamflow data for computation of gains and losses were collected in March 2006 from 36 sites on the Brazos River and 19 sites on 19 tributaries to the Brazos River; and in August 2006 from 28 sites on the Brazos River and 16 sites on tributaries. Hydrograph separation and associated analyses indicate an appreciable increase in base flow as a percentage of streamflow in the reach of the Brazos River that crosses the outcrops of the Carrizo-Wilcox, Queen City, Sparta, and Yegua-Jackson aquifers compared to that in the adjacent upstream reach (on average from about 43 percent to about 60 percent). No increase in base flow as a percentage of streamflow in the reach of the Brazos River crossing the Gulf Coast aquifer compared to that in the adjacent upstream reach was indicated. Streamflow gains and losses computed for March 2006 for 35 reaches defined by pairs of sites on the Brazos River indicated that five reaches were verifiably gaining streamflow (computed gain exceeded potential flow measurement error) and none were verifiably losing streamflow. Four of the five gaining reaches are in the outcrop areas of the Carrizo-Wilcox and Yegua-Jackson aquifers. The results of the synoptic gain and loss surveys are consistent with the results of the base-flow analysis of historical streamflow. Appreciable increases in streamflow, apparently the result of increases in base flow, occur in the reach of the Brazos River that crosses the outcrops of the Carrizo-Wilcox, Queen City, Sparta, and Yegua-Jackson aquifers.
Streamflow, water-quality, and biological data for three tributaries to Lake Houston near Houston, Texas, 2002-04
During 2002-04 the U.S. Geological Survey, in cooperation with the Houston-Galveston Area Council and the Texas Commission on Environmental Quality, conducted a systematic monitoring study on Lake Creek, Peach Creek, and Caney Creek near Houston, Texas, to assess the current water-quality and biological conditions in the three tributaries to Lake Houston. Streamflow and water-quality data (chloride and sulfate, nutrients, biochemical oxygen demand, phytoplankton, indicator bacteria, pesticides, and suspended sediment) were collected at 11 sites, and fish and benthic-macroinvertebrate data were collected at eight of the 11 sites. Graphical comparisons of concentration data for eight water-quality constituents by watershed indicate relatively large differences in concentration distribution among all three watersheds for nitrite plus nitrate nitrogen (medians: Lake, 0.20; Peach, 0.14; and Caney, 0.32 mg/L). Graphical comparisons of these data by season show consistency in distribution of constituent concentrations. The distributions of chlorophyll-a in summer and E. coli bacteria in winter each contain a few relatively large concentrations. Fifty-six species of fish from 15 major families were collected during the study. For all sites except one on Lake Creek, the majority of fish collected were sunfish; minnows dominated at the one Lake Creek site. Invertivores (mostly sunfish and minnows) made up more than 65 percent of the trophic structure, omnivores were the next largest percentage, and piscivores the smallest percentage. Ecoregion-specific index of biotic integrity (ECO-IBI) scores (averages of samples) for three of four upstream Lake Creek sites indicate intermediate aquatic life use, and the most downstream site, high aquatic life use. ECO-IBI scores for the Peach Creek and Caney Creek sites indicate high aquatic life use. The maximum number of aquatic-insect taxa (51) were collected at a site on Peach Creek near Cleveland, and the minimum number of aquatic-insect taxa (17) were collected at site on Caney Creek near New Caney. The benthic-macroinvertebrate index of biotic integrity (B-IBI) scores (averages of samples) for the three upstream Lake Creek sites indicate intermediate aquatic life use, and the B-IBI score for the most downstream site indicates high aquatic life use. B-IBI scores for the Peach Creek sites, in downstream order, are exceptional and high; and scores for the Caney Creek sites, in downstream order, are high and intermediate.
Water-quality assessment of Lake Houston near Houston, Texas, 2000-2004
Lake Houston is a major source of public water supply and recreational resource for the Houston metropolitan area, Texas. Water-quality issues of potential concern for the lake have included nutrient enrichment (orthophosphorus, total phosphorus, nitrite plus nitrate) and aquatic life use (dissolved oxygen). The , in cooperation with the City of Houston, collected water samples from three sites in Lake Houston and from two streams that discharge to the lake during 2000–2004. Nitrogen compounds, phosphorus, suspended sediment, organic carbon, turbidity, chlorophyll-a, and selected pesticide compounds in water were assessed for all sites. Waterquality conditions of the lake and inflow streams were assessed, and loads and yields were computed for selected constituents in the streams. Selected constituents from samples collected in Lake Houston during 1990–2004 were tested for trends. The three sites sampled in Lake Houston characterized water available to the City of Houston pumping station (site AC), water entering the lake from the largely rural eastern subbasin (site EC), and water entering the lake from the more urbanized, western subbasin (site FC). Most constituent concentrations were largest at site FC, smallest at site EC, and intermediate at site AC. Organic nitrogen was the dominant form of nitrogen in samples collected at all sites. Nitrite plus nitrate concentrations were largest at site FC. Total phosphorus concentrations in all samples were larger than that recommended by the U.S. Environmental Protection Agency to limit aquatic growth in reservoirs. There was a wide range in suspended-sediment concentrations and turbidity in the lake. Twelve pesticides were detected. Atrazine and its breakdown product, 2-chloro-4-isopropylamino-6-amino-s-triazine (CIAT), were the most commonly detected pesticides; concentrations of atrazine were larger than the U.S. Environmental Protection Agency maximum contaminant level of 3.0 micrograms per liter in two samples at site FC. The relative contributions to the water quality of Lake Houston from the eastern and western subbasins were examined by collecting water samples in Cypress Creek and East Fork San Jacinto River. Nitrate and pesticide concentrations were larger in Cypress Creek than in East Fork San Jacinto River. In Cypress Creek, nitrate was the primary form of nitrogen at low flows. Atrazine exceeded 3.0 micrograms per liter in three of 17 samples, with the maximum measured concentration of 21.3 micrograms per liter. In East Fork San Jacinto River, organic nitrogen was the primary form of nitrogen. Atrazine was detected in six of 15 samples. The maximum atrazine concentration was 0.233 microgram per liter. Constituent yields allowed direct comparison of loads from Cypress Creek and East Fork San Jacinto River. In Cypress Creek, storm yields of nitrite plus nitrate nitrogen for high flows ranged from 8 to 45 pounds per square mile per day; in East Fork San Jacinto River, the maximum storm yield for high flows was 1.47 pounds per square mile per day. At low flows, the median daily yield of dissolved phosphorus from Cypress Creek was 84 times larger than the median daily yield from East Fork San Jacinto River; at high flows, it was 16 times larger. At high flows, the maximum daily yield of atrazine from Cypress Creek was 460 times larger than the maximum daily yield at high flows from East Fork San Jacinto River. The concentrations of most constituents at Lake Houston sites showed no trend during 1990–2004; however, significant trends overall or for particular seasons, or both, were detected at some sites for nitrite plus nitrate, dissolved phosphorus, dissolved organic carbon, chlorophyll-a, and diazinon (2000–2004 data only for diazinon).
Surface-water hydrologic data for the Houston metropolitan area, Texas, water years 1990-95
During water years 1990–95, data were collected at 24 U.S. Geological Survey streamflow-gaging stations, 21 rain gages, and 6 water-quality stations in the Houston metropolitan area, Texas. The data were collected as part of the Houston Urban Runoff Program, which began in water year 1964. Annual peaks were defined for the 24 streamflow-gaging stations in the study area. All stations had 10 or more years of record. Precipitation data from the 21 rain gages and discharge or stage data from 23 streamflow-gaging stations are available to develop storm hydrographs. One-hundred thirty-four samples were collected at six water-quality stations. The samples were analyzed for about 80 water-quality properties and constituents.
Hydrologic, water-quality, and sediment-quality data for the Christmas Bay system, Brazoria County, Texas, February 1999-March 2000
The Christmas Bay system is a group of three small secondary bays (Christmas, Bastrop, and Drum Bays) at the southwestern end of the Galveston Bay estuarine system in Brazoria County, Texas. During February 1999-March 2000, hydrologic, water-quality, and sediment-quality data were collected from each of the three bays to establish baseline conditions. Gage-height fluctuations closely matched open-water tidal fluctuations. Rainfall during February 1999-February 2000 was about 20 percent below the annual average. Specific conductance, pH, water temperature, and dissolved oxygen monitored at 30-minute intervals in Christmas Bay for 13 months showed seasonal variations typical of monitoring stations on the Texas Gulf Coast. Prevailing winds were from the southeast. Monthly water-quality sampling for 13 months showed that in each of the three bays concentrations of major ions were small, and most nutrient concentrations were at or less than minimum reporting levels; indicator bacteria counts were consistently higher in samples collected from Drum Bay. Several trace elements (sampled twice) were detected in small concentrations. The only organochlorine pesticides (sampled once) that were greater than minimum reporting levels were atrazine, deethylatrazine, metolachlor, and simazine. During February 29-March 29, 2000, three semipermeable membrane devices were deployed at the Christmas Bay monitoring station. Seven of 77 semivolatile organic compounds analyzed in the lipids from the devices were detected in minute amounts. Analyses of surficial bed sediment sampled once in each of the three bays yielded detections of a number of semivolatile organic compounds; all concentrations were less than 10 micrograms per liter and much less than the respective benchmark concentration for those compounds that have had a benchmark concentration established for the protection of aquatic life.
Discharge between San Antonio Bay and Aransas Bay, southern Gulf Coast, Texas, May-September 1999
Along the Gulf Coast of Texas, many estuaries and bays are important habitat and nurseries for aquatic life. San Antonio Bay and Aransas Bay, located about 50 and 30 miles northeast, respectively, of Corpus Christi, are two important estuarine nurseries on the southern Gulf Coast of Texas (fig. 1). According to the Texas Parks and Wildlife Department, “Almost 80 percent of the seagrasses [along the Texas Gulf Coast] are located in the Laguna Madre, an estuary that begins just south of Corpus Christi Bay and runs southward 140 miles to South Padre Island. Most of the remaining seagrasses, about 45,000 acres, are located in the heavily traveled San Antonio, Aransas and Corpus Christi Bay areas” (Shook, 2000). Population growth has led to greater demands on water supplies in Texas. The Texas Water Development Board, the Texas Parks and Wildlife Department, and the Texas Natural Resource Conservation Commission have the cooperative task of determining inflows required to maintain the ecological health of the State’s streams, rivers, bays, and estuaries. To determine these inflow requirements, the three agencies collect data and conduct studies on the need for instream flows and freshwater/ saline water inflows to Texas estuaries. To assist in the determination of freshwater inflow requirements, the U.S. Geological Survey (USGS), in cooperation with the Texas Water Development Board, conducted a hydrographic survey of discharge (flow) between San Antonio Bay and Aransas Bay during the period May–September 1999. Automated instrumentation and acoustic technology were used to maximize the amount and quality of data that were collected, while minimizing personnel requirements. This report documents the discharge measured at two sites between the bays during May–September 1999 and describes the influences of meteorologic (wind and tidal) and hydrologic (freshwater inflow) conditions on discharge between the two bays. The movement of water between the bays is controlled primarily by prevailing winds, tidal fluctuations, and freshwater inflows. An adequate understanding of mixing and physical exchange in the estuarine waters is fundamental to the assessment of the physical, chemical, and biological processes governing the aquatic system.
Estimated effects on water quality of Lake Houston from interbasin transfer of water from the Trinity River, Texas
The City of Houston is considering the transfer of water from the Trinity River to Lake Houston (on the San Jacinto River) to alleviate concerns about adequate water supplies for future water demands. The U.S. Geological Survey, in cooperation with the City of Houston, conducted a study to estimate the effects on the water quality of Lake Houston from the transfer of Trinity River water. A water-quality model, CE–QUAL–W2, was used to simulate six water-quality properties and constituents for scenarios of interbasin transfer of Trinity River water. Three scenarios involved the transferred Trinity River water augmenting streamflow in the East Fork of Lake Houston, and three scenarios involved the transferred water replacing streamflow from the West Fork of the San Jacinto River. The estimated effects on Lake Houston were determined by comparing volume-weighted daily mean water temperature, phosphorus, ammonia nitrogen, nitrite plus nitrate nitrogen, algal biomass, and dissolved oxygen simulated for each of the transfer scenarios to simulations for a base dataset. The effects of the interbasin transfer on Lake Houston do not appear to be detrimental to water temperature, ammonia nitrogen, or dissolved oxygen. Phosphorus and nitrite plus nitrate nitrogen showed fairly large changes when Trinity River water was transferred to replace West Fork San Jacinto River streamflow. Algal biomass showed large decreases when Trinity River water was transferred to augment East Fork Lake Houston streamflow and large increases when Trinity River water was transferred to replace West Fork San Jacinto River streamflow. Regardless of the scenario simulated, the model indicated that light was the limiting factor for algal biomass growth.
Time of travel of solutes in Buffalo Bayou and selected tributaries, Houston, Texas, August 1999
The U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency, conducted a time-of-travel study in the Buffalo Bayou watershed during low flow in August 1999. The study was done as part of the U.S. Environmental Protection Agency Environmental Monitoring for Public Access and Community Tracking (EMPACT) program. The EMPACT program was designed for the U.S. Environmental Protection Agency to work with communities to “make timely, accurate, and understandable environmental information available to millions of people in the largest metropolitan areas across the country.” (U.S. Environmental Protection Agency, 2000). Buffalo Bayou, located in Houston, Texas, was chosen as a pilot project because it is a frequently used recreational water source, it has many water-treatment facilities located along its stream segments, and it has a history of water-quality problems (Houston-Galveston Area Council, 2000). One component of the pilot project is to develop a water-quality simulation model that can be used to assess the effects of noncompliance events on Buffalo Bayou. Because accurate estimates of time of travel during low flow are required to develop the model, the time of travel of solutes in Buffalo Bayou and selected tributaries was determined using dye tracing methods. The study was conducted during low flow in a 38.7-mile reach of Buffalo Bayou, a 9.6-mile reach of Whiteoak Bayou, a 5.9-mile reach of Mason Creek, and a 6.6-mile reach of Bear Creek. Efforts to determine the time of travel in a 7.5-mile reach of Horsepen Creek were unsuccessful. This report explains the approach used to conduct the study and presents the results of the study
Estimation of minimum 7-day, 2-year discharge for selected stream sites, and associated low-flow water-quality data, southeast Texas, 1997-98
The U.S. Geological Survey (USGS) operates a network of streamflow-gaging stations in Texas that provides discharge data used for water-management decisions and various other purposes. Operating stations at all locations where discharge data are needed is not feasible, but the statistical characteristics of the network station data can be used to estimate discharge characteristics at ungaged sites. Regionalization techniques such as regression analyses relate discharge-frequency characteristics to selected physical and climatic characteristics of drainage basins. A particular discharge-frequency characteristic that can be regionalized is the minimum 7-day, 2-year discharge1 (7Q2). In Texas, the 7Q2 is used at stream sites to analyze permit applications for water allocation, water-supply planning, aquatic maintenance (instream flow) requirements, and waste-load allocation for point and nonpoint source discharges.
Nutrient loading and selected water-quality and biological characteristics of Dickinson Bayou near Houston, Texas, 1995-97
Data were collected at 10 stations in the Dickinson Bayou watershed near Houston, Texas, from March 1995 through February 1997 to estimate the concentrations, loads, and yields of selected nutrients that enter the bayou; to characterize the effects on nutrient concentrations of flow conditions, seasonality, and land use; and to identify nutrient sources (point or nonpoint) inferred from the occurrence and abundance of algal species in the benthic algal community. These data included rainfall samples, streamflow measurements, stream-water-quality samples, and biological samples, in addition to quality-assurance/quality-control samples. Estimates of loads of selected nutrients for the 106-square-mile watershed during the study were made for point sources and nonpoint sources. Point-source loading data are available only for ammonia nitrogen. Approximately 21.3 pounds per day of ammonia nitrogen is estimated from point sources during the study period. Nonpoint-source loads are estimated for eight nutrient forms: 7.84 pounds per day of dissolved ammonia nitrogen, 5.79 pounds per day of dissolved nitrite nitrogen, 215 pounds per day of dissolved Kjeldahl nitrogen, 350 pounds per day of total Kjeldahl nitrogen, 40.1 pounds per day of dissolved nitrite plus nitrate nitrogen, 67.6 pounds per day of total phosphorus, 46.6 pounds per day of dissolved phosphorus, and 42.8 pounds per day of dissolved orthophosphate. Rainfall-deposition rates also are estimated for comparison with point- and nonpoint-source loads. Deposition rates are 110 pounds per day of dissolved ammonia nitrogen, 120 pounds per day of dissolved nitrate nitrogen, and 15.8 pounds per day of dissolved phosphorus. Statistical tests were used to determine whether there are significant differences between nutrient concentrations during low-flow and during high-flow conditions. For basins with rural/mixed and urban land uses, nutrient concentrations generally are significantly different (greater) during storm events than during low flow, indicating accumulation in the watershed and subsequent washoff of nutrients. However, nutrient concentrations in storm-event samples consisting predominantly of runoff from a pasture are not significantly greater than those in low-flow samples. Statistical tests for seasonality indicate that dissolved ammonia nitrogen is significantly different in at least one season for all land uses (rural/residential, rural/mixed, and pasture) except urban. Concentrations tend to increase in the spring and early summer months, possibly from fertilizer application and subsequent washoff. Constituent-yield data were used to make direct comparisons of the nonpoint-source load contributions from four stations with watersheds of different land use. These comparisons lead to three conclusions: (1) For all nutrient species except orthophosphate, urban land use is the largest nonpoint-source contributor, (2) Kjeldahl nitrogen is the most abundant nutrient species, and (3) organic nitrogen accounts for the major part of the Kjeldahl nitrogen. Algal samples were collected at seven stations and were analyzed for periphyton identification and enumeration, and chlorophyll a and chlorophyll b concentrations. The large relative abundance of soil algae at stations in the middle of the watershed likely indicates the cumulative effects on water quality of agricultural nonpoint sources. Farther downstream near the State Highway 3 bridge, and downstream of three major tributary inflows, the increase in abundance of soil algae to a larger-than-expected level might reflect water-quality influences from predominantly urban nonpoint sources in the drainage basins of the three major tributary inflows. Nutrient concentrations do not appear to limit algal production in the upper (non-tidal) reach of Dickinson Bayou; but nutrient concentrations could have been limiting benthicalgal production in the lower (tidal) reach of the bayou during the time of the synoptic survey. If nitrogen is the limiting resource for algal productivity in the tidal reach of Dickinson Bayou, eutrophication of the system could be (at least partially) mitigated if nonpoint-source nutrient loads into the Bayou were reduced.
Floods in southeast Texas, October 1994
Rainfall in southeast Texas, which ranged in amounts from about 8 to more than 28 inches during October 15–19, 1994, caused severe flooding in parts of a 38-county area. A combination of meteorological events—residual atmospheric moisture over southern Texas associated with Hurricane Rosa from the Pacific Coast of Mexico and low-level moisture from the Gulf of Mexico drawn inland to a warm front by a strong low-pressure system over the southern Rocky Mountains—spawned vigorous thunderstorms that produced rainfall amounts that may exceed records for the area.