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At least 1,009 records · Page 56Linked to original sources
USGS1990

Structure and application of an interface program between a geographic-information system and a ground-water flow model

A computer-program interface between a geographic-information system and a groundwater flow model links two unrelated software systems for use in developing the flow models. The interface program allows the modeler to compile and manage geographic components of a groundwater model within the geographic information system. A significant savings of time and effort is realized in developing, calibrating, and displaying the groundwater flow model. Four major guidelines were followed in developing the interface program: (1) no changes to the groundwater flow model code were to be made; (2) a data structure was to be designed within the geographic information system that follows the same basic data structure as the groundwater flow model; (3) the interface program was to be flexible enough to support all basic data options available within the model; and (4) the interface program was to be as efficient as possible in terms of computer time used and online-storage space needed. Because some programs in the interface are written in control-program language, the interface will run only on a computer with the PRIMOS operating system. (USGS)

Open-File Report↗
USGS1995

Structure of the basins and ranges, Southwest New Mexico, an interpretation of seismic velocity sections

This report presents a geologic appraisal of seismic velocity sections that profile a total of 790 km in southwest New Mexico west of Las Cruces and south of Lordsburg and Deming. The present work outlines the contribution of these velocity sections to estimating areas favorable for mineral resource occurrences. Seismic refraction surveys are carried out with the initial goal of estimating the subsurface distribution of acoustic compressional velocity (Vp), which may ultimately be interpreted to provide information on lithology, geologic structure, and the occurrence of natural resources. The seismic sections presented here show velocity detail having dimensions of 100's to 1000's of meters to a depth of about 2.5 km, and across a net of traverses that profile most basins well as several ranges in the study area. Figure 1 shows the location of the seismic refraction lines. The lines are designated 1, 2, 3, 4, 5, and 7; there is no line 6. The survey covers a broad swath of the southwest Basin and Range Province extending from the Arizona border eastward to the Rio Grande River, and from the Mexican border to about lat. 32° 30' N. Lines 1, 3, and 7 traverse the axis of basins in roughly northsouth directions; the remaining lines 2, 4, and 5 trend east-west and cross various ranges and basins. Seismic data that have been collected in this region include deep-crustal refraction traverses by university scientists and commercial seismic reflection profiles acquired for petroleum exploration. Results of deep-crustal refraction studies are reviewed to provide a regional setting for the higher resolution refraction data. Results from seismic reflection will not be discussed. Industry reflection data in the area are not generally available for non-proprietary use. The nearest reflection data publicly available are in the Socorro area, about 80 km north of the present study area (Brown and others, 1980). These data were acquired by the Consortium for Continental Reflection Profiling (COCORP), a public-supported research group, to investigate the possibility of magma beneath part of the Rio Grande valley. Up to 1978 there were about 36 deep borings in the region of southwest New Mexico (Thompson and others, 1978). This drilling resulted mainly from an evaluation of petroleum potential of the Pedrogosa basin which is an extensive area of Paleozoic subsidence in Arizona, New Mexico, and Mexico that accumulated about three kilometers of Paleozoic sedimentary rock (Zeller, 1965; Thompson and others, 1978). Of these drill holes, 25 are close enough to the present seismic sections to provide correlations of velocity to lithology, and to provide an estimate of the errors associated with depth-to-interface interpretations. This information is summarized prior to considering the implications of the seismic sections in detail. The major portion of the report centers around two plates: Plate I shows seismic lines and selected drill hole locations superimposed on gravity contours, and Plate II shows velocitysections with drill hole summaries. These plates provide the foundation for developing inferences on buried lithologic, structural, and mineral resources for the region.

New Mexico↗
USGS1996

Sublake geologic structure from high-resolution seismic-reflection data from four sinkhole lakes in the Lake Wales Ridge, central Florida

Seismic-reflection profiles from Lake Wales, Blue Lake, Lake Letta, and Lake Apthorp located along the Lake Wales Ridge in central Florida provide local detail within the regional hydrogeologic framework as described by litho- and hydrostratigraphic cross sections. Lakes located with the mantled karst region have long been considered to be sinkhole lakes, originating from subsidence activity. High-resolution seismic- reflection data confirm this origin for these four lakes. The geologic framework of the Lake Wales Ridge has proven to be a suitable geologic setting for continuous high-resolution seismic-reflection profiling in lakes; however, the nature of the lake-bottom sediments largely controls the quality of the seismic data. In lakes with significant organic-rich bottom deposits, interpretable record was limited to areas where organic deposits were minimal. In lakes with clean, sandy bottoms, the seismic-reflection methods were highly successful in obtaining data that can be correlated with sublake subsidence features. These techniques are useful in examining sublake geology and providing a better understanding of how confining units are affected by subsidence in a region where their continuity is of significant importance to local lake hydrology. Although local geologic control around each lake generally corresponds to the regional geologic framework, local deviations from regional geologic trends occur in sublake areas affected by subsidence activity. Each of the four lakes examined represents a unique set of geologic controls and provides some degree of structural evidence of subsidence activity. Sublake geologic structures identified include: (1) marginal lake sediments dipping into bathymetric lows, (2) lateral discontinuity of confining units including sags and breaches, (3) the disruption and reworking of overlying unconsolidated siliciclastic sediments as they subside into the underlying irregular limestone surface, and (4) sublake regions where confining units appear to remain intact and unaffected by nearby subsidence activity. Each lake likely is underlain by several piping features rather than one large subsidence feature.

Florida↗
USGS1999

Structural relationships of pre-Tertiary rocks in the Nevada Test Site region, southern Nevada

This report contains a synthesis and interpretation of structural and stratigraphic data for pre-Tertiary rocks in a large area of southern Nevada within and near the Nevada Test Site. Its presents descriptive and interpretive information from discontinuously exposed localities in the context of a regional model that integrates stratigraphy, sedimentology, crustal structure, and deformational style and timing. Evidence is given for substantial strike-slip faults, for modest excursion on low-angle faults, and for pre-Oligocene formation of the regional oroclinal flexure in neighboring mountain ranges.

Professional Paper↗
USGS2005

Crystalline-rock ejecta and shocked minerals of the Chesapeake Bay impact structure, USGS-NASA Langley core, Hampton, Virginia, with supplemental constraints on the age of impact

The USGS-NASA Langley corehole at Hampton , Va., was drilled 2000 as the first in a series of new coreholes drilled in the late Eocene Chesapeake Bay impact structure to gain a comprehensive understanding of its three-dimensional character. This understanding is important for assessing ground-water resources in the region, as well as for learning about marine impacts on Earth. We studied crystalline-rock ejecta and shock-metamorphosed minerals from the Langley core to determine what they reveal about the geology of crystalline rocks beneath the Atlantic Coastal Plain and how those rocks were affected by the impact . An unusual polymict diamicton, informally called the Exmore beds (upper Eocene), is 33.8 meters (m; 110.9 feet (ft)) thick and lies at a depth of 269.4 to 235.65 m (884.0 to 773.12 ft) in the core . This matrix-supported sedimentary deposit contains clasts of Tertiary and Cretaceous sediment (ranging up to boulder size) and sparse pebbles of crystalline rock . The matrix consists of muddy sand that contains abundant quartz grains and minor glauconite and potassium feldspar. Significantly, the sandy matrix of the Exmore beds contains sparse quartz grains (0.1 to 0.3 millimeter (0.004 to 0.012 inch) in diameter) that contain multiple sets of intersecting planar deformation features formerly referred to as shock lamellae. As many as five different sets have been observed in some quartz grains. Planar deformation features also occur in quartz grains in reworked crystalline-rock clasts in the Exmore beds. Such grains are clearly of shock-metamorphic origin. The presence of these features indicates that the quartz grains have experienced pressures greater than 6 gigapascals (GPa) and strain rates greater than 10 6 /second. Thus, the shock-metamorphosed quartz grains, although rare, provide clear and convincing evidence that the Exmore beds are of hybrid impact origin. Identification of shocked quartz grains in the Langley core adds to the number of sites in the structure where their presence is confirmed. Most of the clasts of crystalline rock that are in and just below the Exmore beds are rounded, detrital, and typical of coastal plain sediments. However, a few have angular shapes and consist of cataclastically deformed felsite having aphanitic-porphyritic to aphanitic texture and peraluminous rhyolite composition. Three of these clasts contain quartz grains that display two sets of planar deformation features of shock-metamorphic origin. Shock-metamorphosed quartz is an integral part of the cataclastic fabric in these three clasts, indicating that both the fabric and the shocked quartz were produced by the same high-energy impact event. Some felsite clasts have spherulitic textures that may be features either of an impact melt or of preimpact volcanic rocks. A weighted-mean total-fusion 40 Ar/ 39 Ar age of 35.3±0.1 Ma (±lσ) for 19 analyses of 4 North American tektites records the age of the late Eocene Chesapeake Bay impact event.

Chesapeake Bay↗
USGS2008

Maps showing geology, structure, and geophysics of the central Black Hills, South Dakota

This 1:100,000-scale digital geologic map details the complex Early Proterozoic granitic rocks, Early Proterozoic supracrustal metamorphic rocks, and Archean crystalline basement of the Black Hills. The granitic rocks host pegmatite deposits renowned for their feldspar, mica, spodumene, and beryl. The supracrustal rocks host the Homestake gold mine, which produced more than 40 million ounces of gold over a 125-year lifetime. The map documents the Laramide deformation of Paleozoic and Mesozoic cover rocks; and shows the distribution of Laramide plutonic rocks associated with precious-metals deposits. Four 1:300,000-scale maps summarize Laramide structures; Early Proterozoic structures; aeromagnetic anomalies; and gravity anomalies. Three 1:500,000-scale maps show geophysical interpretations of buried Early Proterozoic to Archean rocks in western South Dakota and eastern Wyoming.

South Dakota↗
USGS2023

Colored shaded-relief bathymetric map and orthomosaic from structure-from-motion quantitative underwater imaging device with five cameras of the Lake Tahoe floor, California

This two-sheet publication displays a high-resolution colored shaded-relief bathymetric map (sheet 1) and orthomosaic (sheet 2) of part of the Lake Tahoe floor in California generated from a U.S. Geological Survey towed surface vehicle with multiple downward-looking underwater cameras. The system is named the Structure-from-Motion Quantitative Underwater Imaging Device with Five Cameras (SQUID-5). The cameras were synchronized with each other and with a survey-grade Global Navigation Satellite System. A total of 42,939 photographs were collected with nearly complete overlapping coverage of an area approximately 250 meters by 250 meters. A digital terrain model and an orthomosaic were generated from the overlapping photographs using Structure-from-Motion and photogrammetry techniques. Gaps are present in the bathymetry data owing to data-collection or -processing artifacts. These two sheets display the very fine details of the lake floor mapped using SQUID-5.

California↗
USGS2008

Three-Dimensional Geologic Model of Complex Fault Structures in the Upper Seco Creek Area, Medina and Uvalde Counties, South-Central Texas

This multimedia report shows and describes digital three-dimensional faulted geologic surfaces and volumes of the lithologic units of the Edwards aquifer in the upper Seco Creek area of Medina and Uvalde Counties in south-central Texas. This geologic framework model was produced using (1) geologic maps and interpretations of depositional environments and paleogeography; (2) lithologic descriptions, interpretations, and geophysical logs from 31 drill holes; (3) rock core and detailed lithologic descriptions from one drill hole; (4) helicopter electromagnetic geophysical data; and (5) known major and minor faults in the study area. These faults were used because of their individual and collective effects on the continuity of the aquifer-forming units in the Edwards Group. Data and information were compared and validated with each other and reflect the complex relationships of structures in the Seco Creek area of the Balcones fault zone. This geologic framework model can be used as a tool to visually explore and study geologic structures within the Seco Creek area of the Balcones fault zone and to show the connectivity of hydrologic units of high and low permeability between and across faults. The software can be used to display other data and information, such as drill-hole data, on this geologic framework model in three-dimensional space.

Scientific Investigations Report↗
USGS2012

Integration of new geologic mapping and satellite-derived quartz mapping yields insights into the structure of the Roberts Mountains allochthon applicable to assessments for concealed Carlin-type gold deposits

Geologic mapping and remote sensing across north-central Nevada enable recognition of a thick sheet of Middle and Upper Ordovician Valmy Formation quartzite that structurally overlies folded and faulted Ordovician through Devonian stratigraphic units of the Roberts Mountains allochthon. In the northern Independence Mountains and nearby Double Mountain area, the Valmy Formation is in fault contact with Ordovician through Silurian, predominantly clastic, sedimentary rocks of the Roberts Mountains allochthon that were deformed prior to, or during, emplacement of the Valmy thrust sheet. Similar structural relations are recognized discontinuously for 200 kilometers along the strike of the Roberts Mountains allochthon in mapping guided by regional remote-sensing-based (ASTER) quartz maps. Overall thicknesses of deformed Roberts Mountains allochthon units between the base of the Valmy and the top of underlying carbonate rocks that host large Carlin-type gold deposits varies on the order of hundreds of meters but is not known to exceed 700 meters. The base of the Valmy thrust sheet is a complimentary datum in natural resource exploration and mineral resource assessment for concealed Carlin-type gold deposits.

Nevada↗
USGS1979

Hydrology and water quality in the Nederlo Creek Basin, Wisconsin, before construction of two water-retention structures

The Nederlo Creek basin, in the "Driftless Area" of southwest Wisconsin, is geographically and hydrologically similar to other small basins in the area. Topography is rugged, with approximately 400 feet of relief between the boundary ridge tops and the valley floor. The water-retention structures (a dry floodwater- retention structure and a 43-acre reservoir) are to provide recreation and flood protection for the basin. Streamflow, springflow, precipitation, and groundwater levels were monitored at several sites to describe the hydrologic system. Streamflow is fairly constant at base flow, but rapid changes in discharge occur during periods of snowmelt or heavy rain; recession to base-flow discharge following these events is rapid. Surface runoff is a significant contributor to Streamflow only 10 percent of the time. The mean annual hydrologic budget for water years 1968-72 shows that of the 32.5 inches of precipitation on the basin, 6.4 inches left as runoff and 25.9 inches as evapotranspiration; ground-water storage increased an average of 0.2 inches per year. The water is a hard calcium magnesium bicarbonate type. Concentrations of major constituents in ground water and streams at base flow are similar, but concentrations in the stream generally decrease during periods when surface runoff contributes to Streamflow. Dissolved-oxygen concentrations in the stream are generally lowest during the summer; nighttime lows are generally between 7 and 8 milligrams per liter and daily maximums between 11 and 12.5 milligrams per liter. Diurnal water-temperature fluctuations of several degrees are common in streams during summer; daily maximum water temperatures as high as 26°C have been measured in some areas, but temperatures this high seldom persist for more than 2 hours. Estimates of mean annual total phosphorus and total nitrogen loads during 1967-74 fall within the ranges of 0.02 to 0.07 and 0.4 to 0.8 tons per square mile, respectively; 70 to 80 percent of the total phosphorus and 35 to 55 percent of the total nitrogen are transported during periods when surface runoff contributes to Streamflow. Mean annual suspended-sediment loads during 1968-74 range from 13 to 60 tons per square mile, with 74 to 86 percent of the total transported during periods when surface water contributes to streamflow. These sediment loads are at the low end of the range previously reported for streams in the "Driftless Area".

Wisconsin↗
USGS1982

Effects of a floodwater-retarding structure on the hydrology and ecology of Trout Creek in southwestern Wisconsin

The primary effects of a floodwater-retarding structure (FRS) on the streamflow of Trout Creek, Wisconsin, are attenuation of flood peaks and extension of the time base of flood hydrographs. Reduction of flood peaks ranged from 58 to 91 percent during the study period from 1975 to 1979. There is an inverse relation between sediment concentration and outflow from the FRS during floods. As water went into storage in the flood pool in March 1976, the daily-mean total-sediment concentration in the FRS outflow dropped from 562 to 147 milligrams per liter. Sediment concentration subsequently increased to 809 milligrams per liter as the discharge from the FRS dropped; concentrations remained more than 400 milligrams per liter for several weeks thereafter. Most sediment stored in the flood pool during flood flows is released from the reservoir during subsequent reduced discharge. Sediment trapping efficiency of the FRS was about 7 percent for the 4-year period of the study. The bankfull capacity of the channel was reduced from 154 cubic feet per second upstream from the flood pool of the FRS to 65 cubic feet per second just downstream from the FRS. This latter discharge corresponds closely to the normal FRS outflow of 58 to 71 cubic feet per second during floods. Mean bankfull depth downstream from the FRS has adjusted to a value 45 percent less than upstream from the structure due to sedimentation of materials transported from the FRS during reduced flows. The hydraulic geometry and relationships between channel geometry and drainage area indicate little effect of the FRS near the mouth of Trout Creek, 2.4 miles downstream from the FRS. The arthropod fauna of Trout Creek is large and diverse. No effects of the FRS on these fauna were observed from April 1975 to October 1979. From fall 1975 to winter 1978, the most important factor contributing to increased brown trout egg survival and fry emergence in Trout Creek during a single reproductive season is higher water temperatures in the upper reaches of the stream. The FRS was not found to have any significant effect on trout reproduction during that period. From 1960 to 1979, winter floods seem to have had the greatest adverse effect on the survival of brown trout eggs and sac fry. Although construction of the FRS has eliminated some spawning gravels in the flood pool owing to sedimentation, the wild trout have adapted by using spawning grounds above the flood pool more extensively and intensively. The FRS has not blocked the upstream migration of spawning trout, but it has eliminated similar migrations of fish that compete with and prey on the trout. Controlled streamflows downstream from the FRS have had a stabilizing influence on the limited trout reproduction in this region.

Wisconsin↗
USGS1986

Surficial geology, structure, and thickness of selected geohydrologic units in the Columbia Plateau, Washington

A 2-1/2 year study of the Columbia Plateau in Washington was begun in March 1982 to define spatial and temporal variations in dissolved sodium in the Columbia River Basalt Group aquifers and to relate these variations to the groundwater system and its geologic framework. This report describes the geologic framework , including the vertical and areal extent of the major basalt units, interbeds, and overlying materials. Thickness and structure of the Grande Ronde, Wanapum, and Saddle Mountains Basalts, thickness of the interbeds between the Grande Ronde and Wanapum, and Wanapum and Saddle Mountains Basalts, and thickness of the overburden were mapped at a scale of 1:500,000. Information was compiled from 2,500 well records using chemical analyses of core or drill chips, geophysical logs, and driller 's logs, in decreasing order of reliability. Surficial geology and surficial expression of structural features were simplified from published maps to provide maps with this information at the 1:500,000 scale. This report is intended to serve as a base for evaluating the distribution of dissolved sodium in basalt aquifers and as a base for future water resource studies. (USGS)

Water-Resources Investigations Report↗
USGS1986

Divisions of potential fracture permeability, based on distribution of structures and lineaments, in sedimentary rocks of the Rocky Mountains-High Plains region, Western United States

The principal map show geologic structures and lineaments that indicate fracture traces in sedimentary rocks in all or parts of Arizona, Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, Utah, and Wyoming. Fractures associated with geologic structures and lineaments may affect the potential fracture permeability of consolidated rocks. Divisions indicating differences in the potential fracture permeability are delineated on the map.

Arizona, Colorado, Kansas, Nebraska, New Mexico, O↗
USGS1988

Geologic structure and altitude of the top of the Minnelusa Formation, northeastern Black Hills, South Dakota

This map shows the altitude of the top of the Permian--and Pennsylvanian age Minnelusa Formation, the deepest aquifer in the northeastern Black Hills for which there is sufficient data available to construct a structural map. The Minnelusa Formation outcrops in the western part of the map area and is more than 3 ,600 ft below land surface in the northeastern corner of the area. The formation consists of interbedded sandstone, sandy dolomite and limestone, shale, siltstone, gypsum, and anhydrite. The upper beds are an aquifer and the lower beds are a confining or semi-confining unit. Small anticlines and synclines parallel the Minnelusa outcrop. Domal structures and peaks in the study area are the result of Tertiary-age intrusions. (USGS)

Water-Resources Investigations Report↗
USGS1986

Plan of study for the regional aquifer-system analysis of the San Juan structural basin, New Mexico, Colorado, Arizona, and Utah

The San Juan structural basin is an 18,000 sq mi area that contains several extensive aquifers. The basin includes three surface drainage basins and parts of New Mexico, Colorado, Arizona, and Utah. Surface water in the area is fully appropriated, and the steadily increasing demand for groundwater has resulted in water supply concerns. Competition is great between mining and electric power companies, municipalities, and Indian communities for the limited groundwater supplies. This report outlines a 4-year plan for a study of the regional aquifer system in the San Juan structural basin. The purposes of the study are to define and understand the aquifer system; to assess the effects of groundwater use on the aquifers and streams; and to determine the availability and quality of groundwater in the basin. (Author 's abstract)

Water-Resources Investigations Report↗
USGS1995

Surface-water-quality assessment of the upper Illinois River Basin in Illinois, Indiana, and Wisconsin: Analysis of relations between fish-community structure and environmental conditions in the Fox, Des Plaines, and Du Page River basins in Illinois, 1982-84

Multivariate analyses of fish-community, water- quality, streambed-sediment-quality, and habitat data collected from 1982 through 1984 in the Fox, Des Plaines, and Du Page River Basins in northeastern Illinois indicate that fish-community structure was strongly related to water-quality gradients commonly associated with differences between agricultural and urban land uses. Detrended correspondence analysis (DCA) and the Alternate Index of Biotic Integrity (AIBI) tended to group fish communities by river basin. Streams in the predominantly agricultural Fox River Basin tended to have similar DCA scores, the highest AIBI scores, and relatively diverse fish communities that usually included several intolerant species. Streams in the more heavily urbanized Chicago, Little Calumet, Des Plaines, and Du Page River Basins tended to have lower AIBI scores and fish communities dominated by fewer; more tolerant species. Correlative (Spearman's rho) and graphical analyses showed that DCA and AIBI scores for nonwadable sites were more strongly related to water qualiity and streambed- sediment quality than to habitat conditions. DCA and AIBI scores for wadable sites were most strongly related to water quality, were not related to streambed-sediment quality, and were moderately related to habitat variables indicative of stream size. Streams in the Fox River Basin had the smallest concentrations of chemical constituents commonly associated with anthropogenic sources. Streams in the heavily urbanized Des Plaines and Du Page River Basins had larger concentrations of chemical constituents associated with urban runoff and point-sourca discharges. Although fish-community structure was strongly related to the water quality, U.S. Environmental Protection Agency acute and chronic criteria for the protection of freshwater aquatic life were exceeded at few stations. These fish communities may have been responding either to concentrations below the U.S. Environmental Protection Agency criteria or to cumulative or synergistic effects of overall water quality.

Illinois, Indiana, Wisconsin↗
USGS1994

Hydraulic modeling of stream channels and structures in Harbor and Crow Hollow Brooks, Meriden, Connecticut

Effects of urbanization have increased the frequency and size of floods along certain reaches of Harbor Brook and Crow Hollow Brook in Meriden, Conn. A floodprofile-modeling study was conducted to model the effects of selected channel and structural modifications on flood elevations and inundated areas. The study covered the reach of Harbor Brook downstream from Interstate 691 and the reach of Crow Hollow Brook downstream from Johnson Avenue. Proposed modifications, which include changes to bank heights, channel geometry, structural geometry, and streambed armoring on Harbor Brook and changes to bank heights on Crow Hollow Brook, significantly lower flood elevations. Results of the modeling indicate a significant reduction of flood elevations for the 10-year, 25-year, 35-year, 50-year, and 100-year flood frequencies using proposed modifications to (1 ) bank heights between Harbor Brook Towers and Interstate 691 on Harbor Brook, and between Centennial Avenue and Johnson Avenue on Crow Hollow Brook; (2) channel geometry between Coe Avenue and Interstate 69 1 on Harbor Brook; (3) bridge and culvert opening geometry between Harbor Brook Towers and Interstate 691 on Harbor Brook; and (4) channel streambed armoring between Harbor Brook Towers and Interstate 691 on Harbor Brook. The proposed modifications were developed without consideration of cost-benefit ratios.

Water-Resources Investigations Report↗
USGS1996

Description and field analysis of a coupled ground-water/surface-water flow model (MODFLOW/BRANCH) with modifications for structures and wetlands in southern Dade County, Florida

A coupled surface-water model (BRANCH) and ground-water model (MODFLOW) model were tested to simulate the interacting wetlands/surface-water/ ground-water system of southern Dade County. Several options created for the MODFLOW ground- ground-water model were used in representing this field situation. The primary option is the MODBRANCH interfacing software, which allows leakage to be accounted for between the MODFLOW ground-water model and the BRANCH dynamic model for simulation of flow in an interconnected network of open channels. A modification to an existing software routine, which is referred to as BCF2, allows cells in MODFLOW to rewet when dry--a requirement in representing the seasonal wetlands in Dade County. A companion to BCF2 is the modified evapotranspiration routine EVT2. The EVT2 routine changes the cells where evapotranspiration occurs, depending on which cells are wet. The Streamlink package represents direct connections between the canals and wetlands at locations where canals open directly into overland flow. Within the BRANCH model, the capability to represent the numerous hydraulic structures, gated spillways, gated culverts, and pumps was added. The application of these modifications to model surface-water/ground-water interactions in southern Dade County demonstrated the usefulness of the coupled MODFLOW/BRANCH model. Ground-water and surface-water flows are both simulated with dynamic models. Flow exchange between models, intermittent wetting and drying, evapotranspiration, and hydraulic structure operations are all represented appropriately. Comparison was made with a simulation using the RIV1 package instead of MODBRANCH to represent the canals. RIV1 represents the canals by user-defined stages, and computes leakage to the aquifer. Greater accuracy in reproducing measured ground- water heads was achieved with MODBRANCH, which also computes dynamic flow conditions in the canals, unlike RIV1. The surface-water integrated flow and transport two-dimensional model (SWIFT2D) was also applied to the southeastern coastal wetlands for comparison with the wetlands flow approximation made in MODFLOW. MODFLOW simulates the wetlands as a highly conductive upper layer of the aquifer, whereas SWIFT2D solves the hydrodynamic equations. Comparison in this limited test demonstrated no specific advantage for either method of representation. However, much additional testing on a wider variety of geometric and hydraulic situations, such as in areas with greater tidal or other dynamic forcing effects, is needed to make definite conclusions. A submodel of the existing southern Dade County model schematization was used to examine water-delivery alternatives proposed by the U.S. Army Corps of Engineers. For this application, the coupled MODFLOW/BRANCH model was used as a design tool. A new canal and several pumps to be tested to maintain lower water levels in a residential area (while water levels in the Everglades are raised) were added to the model schematization. The pumps were assumed to have infinite supply capacity in the model so that their maximum pumping rates during the simulation could be used to determine pump sizes.

Water-Resources Investigations Report↗