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At least 721 records · Page 40Linked to original sources
USGS2009

Land Area Change and Overview of Major Hurricane Impacts in Coastal Louisiana, 2004-08

The U.S. Geological Survey (USGS) assessed changes in land and water coverage in coastal Louisiana within 2 months of Hurricane Gustav (September 1, 2008) and Hurricane Ike (September 13, 2008) by using Landsat Thematic Mapper (TM) satellite imagery. The purpose of this study was twofold: (1) to provide preliminary information on land-water area changes in coastal Louisiana shortly after Hurricanes Ike and Gustav made landfall and (2) to contrast these changes with prior, widespread land area changes caused by Hurricane Katrina (August 29, 2005) and Hurricane Rita (September 24, 2005) 3 years earlier. Hurricane Gustav's physical surge impacts were not as severe as those observed from Hurricane Katrina. The largest observed changes were the reversion of recovery vegetation in Upper Breton Sound to an immediate post-Katrina appearance. Hurricane Ike's surge impacts were similar, although of somewhat lesser magnitude than Hurricane Rita's surge impacts. Major surge-removed marsh occurred in similar locations with similar morphologies from the two westward tracking storms. Although the net reduction in land from 2004 to 2008 (849.5 km2) exceeded that from 1978 to 2004 (743.3 km2), it is likely that the 2004-08 estimate will decrease, given time for the coast to recover from those hurricane seasons. Nevertheless, it is likely that the cumulative loss from these hurricane seasons will remain significant. Estimation of permanent losses cannot be made until several growing seasons have passed and the transitory impacts of the hurricanes are accounted for.

Scientific Investigations Map↗
USGS2009

Status of Groundwater Levels and Storage Volume in the Equus Beds Aquifer Near Wichita, Kansas, January 2009

Beginning in the 1940s, the Wichita well field was developed in the Equus Beds aquifer in southwestern Harvey County and northwestern Sedgwick County to supply water to the city of Wichita (Williams and Lohman, 1949). In addition to supplying drinking water to the largest city in Kansas, the other primary use of water from the Equus Beds aquifer is to irrigate crops in this agriculture-dominated part of south-central Kansas (Rich Eubank, Kansas Department of Agriculture, Division of Water Resources, oral commun., 2008). The decline of water levels in the aquifer were noted soon after the development of the Wichita well field began (Williams and Lohman, 1949). As water levels in the aquifer decline, the volume of water stored in the aquifer decreases and less water is available to supply future needs. For many years the U.S. Geological Survey (USGS), in cooperation with the city of Wichita, has monitored these changes in water levels and the resulting changes in storage volume in the Equus Beds aquifer as part of Wichita's effort to effectively manage this resource. In 2007, the city of Wichita began using Phase I of the Equus Beds Aquifer Storage and Recovery (ASR) project for large-scale artificial recharge of the Equus Beds aquifer. The ASR project uses water from the Little Arkansas River - either pumped from the river directly or from wells in the riverbank that obtain their water from the river by induced infiltration - as the source of artificial recharge to the Equus Beds aquifer (City of Wichita, 2009).

Scientific Investigations Map↗
USGS2009

Groundwater-Quality Survey of the South Coast Aquifer of Puerto Rico, April 2 through May 30, 2007

The increased potential for variability of groundwater quality in the South Coast aquifer of Puerto Rico due to saline water encroachment from the Caribbean Sea and from deep parts of the aquifer has become a major concern of water planners and managers. In an effort to determine the extent and sources of this encroachment, the U.S. Geological Survey (USGS) and the Puerto Rico Department of Natural and Environmental Resources conducted a synoptic groundwater-quality survey from April 2 through May 30, 2007, for the South Coast aquifer between Ponce and Arroyo (fig. 1). Groundwater resources in this aquifer extend 150 square miles in south-central Puerto Rico and provide an estimated 44.2 million gallons per day (Mgal/d) or about 61 percent of the total water needs. This amount includes: 15.3 Mgal/d for irrigation, 27.4 Mgal/d for public supply, and 1.5 Mgal/d for industrial and other uses (W.L. Molina-Rivera, U.S. Geological Survey, written commun., 2007). Since 1980 when most of the south coastal plain was intensively cultivated for sugarcane, total groundwater withdrawals have declined about 32 Mgal/d with the greatest decline occurring in irrigation (37.2 Mgal/d) and the greatest increase occurring in public supply (5.5 Mgal/d). Although withdrawals have declined substantially, a major concern is that aquifer recharge provided by irrigation return flow from surface-water irrigation canals has essentially dropped to zero because of the large-scale implementation of groundwater drip irrigation systems.

Scientific Investigations Map↗
USGS2009

Estimated land-surface subsidence in Harris County, Texas, 1915-17 to 2001

Land-surface subsidence, or land subsidence, in Harris County, Texas, which encompasses much of the Houston area, has been occurring for decades. Land subsidence has increased the frequency and extent of flooding, damaged buildings and transportation infrastructure, and caused adverse environmental effects. The primary cause of land subsidence in the Houston area is withdrawal of groundwater, although extraction of oil and gas also has contributed. Throughout most of the 20th century, groundwater was the primary source of municipal, agricultural, and industrial water supply for Harris County. Currently (2009) a transition to surface water as the primary source of supply, guided by a groundwater regulatory plan developed by the Harris-Galveston Subsidence District (2001), is in effect. The aquifers in Harris County contain an abundant amount of potable groundwater, but they also contain layers of clay. Groundwater withdrawals caused compaction of the clay layers, which in turn resulted in the widespread, substantial land-surface subsidence that has occurred in the Houston area.

Scientific Investigations Map↗
USGS2010

Conifer health classification for Colorado, 2008

Colorado has undergone substantial changes in forests due to urbanization, wildfires, insect-caused tree mortality, and other human and environmental factors. The U.S. Geological Survey Rocky Mountain Geographic Science Center evaluated and developed a methodology for applying remotely-sensed imagery for assessing conifer health in Colorado. Two classes were identified for the purposes of this study: healthy and unhealthy (for example, an area the size of a 30- x 30-m pixel with 20 percent or greater visibly dead trees was defined as ?unhealthy?). Medium-resolution Landsat 5 Thematic Mapper imagery were collected. The normalized, reflectance-converted, cloud-filled Landsat scenes were merged to form a statewide image mosaic, and a Normalized Difference Vegetation Index (NDVI) and Renormalized Difference Infrared Index (RDII) were derived. A supervised maximum likelihood classification was done using the Landsat multispectral bands, the NDVI, the RDII, and 30-m U.S. Geological Survey National Elevation Dataset (NED). The classification was constrained to pixels identified in the updated landcover dataset as coniferous or mixed coniferous/deciduous vegetation. The statewide results were merged with a separate health assessment of Grand County, Colo., produced in late 2008. Sampling and validation was done by collecting field data and high-resolution imagery. The 86 percent overall classification accuracy attained in this study suggests that the data and methods used successfully characterized conifer conditions within Colorado. Although forest conditions for Lodgepole Pine (Pinus contorta) are easily characterized, classification uncertainty exists between healthy/unhealthy Ponderosa Pine (Pinus ponderosa), Pi?on (Pinus edulis), and Juniper (Juniperus sp.) vegetation. Some underestimation of conifer mortality in Summit County is likely, where recent (2008) cloud-free imagery was unavailable. These classification uncertainties are primarily due to the spatial and temporal resolution of Landsat, and of the NLCD derived from this sensor. It is believed that high- to moderate-resolution multispectral imagery, coupled with field data, could significantly reduce the uncertainty rates. The USGS produced a four-county follow-up conifer health assessment using high-resolution RapidEye remotely sensed imagery and field data collected in 2009.

Scientific Investigations Map↗
USGS2010

Concentration of 1,4-Dioxane in Wells Sampled During 2002-2009 in the Vicinity of the Tucson International Airport Area Superfund Site, Arizona

Extensive groundwater contamination resulting from industrial activities led to the listing of the Tucson International Airport Area as a Superfund Site in 1983. Early investigations revealed elevated levels of volatile organic compounds (VOCs) including the chlorinated solvents trichloroethylene (TCE) and perchloroethylene (PCE) in wells in the area. Several responsible parties were identified and cleanup activities were begun in the late 1980s using technology designed for removal of VOCs. In 2002, the compound 1,4-dioxane was discovered in wells in the Tucson Airport Remediation Project (TARP) area. Since then, 1,4-dioxane has been detected throughout the TARP area, in some cases exceeding the U.S. Environmental Protection Agency (USEPA) drinking water advisory level of 3 ?g/L.

Scientific Investigations Map↗
USGS2010

Sedimentation Survey of Lago de Cidra, Puerto Rico, August 2007

Lago de Cidra is a reservoir located on the confluence of Rio de Bayamon, Rio Sabana, and Quebrada Prieta, in the municipality of Cidra in east-central Puerto Rico, about 3.0 kilometers northeast of the town of Cidra. The dam is owned and operated by the Puerto Rico Aqueduct and Sewer Authority (PRASA), and was constructed in 1946 as a 6.54-million-cubic-meter supplemental water supply for the San Juan metropolitan area. The reservoir impounds the waters of Rio de Bayamon, Rio Sabana and Quebrada Prieta. The reservoir has a drainage area of 21.4 square kilometers. The dam is a concrete gravity and earthfill structure with a length of approximately 165 meters and a structural height of 24 meters. The spillway portion of the dam is an ungated ogee crest about 40 meters long with a crest elevation of 403.00 meters above mean sea level. Additional information and operational procedures are listed in Soler-Lopez (1999). During August 14-15, 2007, the U.S. Geological Survey (USGS), Caribbean Water Science Center (CWSC), in cooperation with the PRASA, conducted a bathymetric survey of Lago de Cidra to update the reservoir storage capacity and actualize the reservoir sedimentation rate by comparing the 2007 data with the previous 1997 bathymetric survey data. The purpose of this report is to describe and document the USGS sedimentation survey conducted at Lago de Cidra during August 2007, including the methods used to update the reservoir storage capacity, sedimentation rates, and areas of substantial sediment accumulation since 1997.

Scientific Investigations Map↗
USGS2010

Sedimentation Survey of Lago Patillas, Puerto Rico, March 2007

Lago Patillas is a reservoir located on the confluence of Rio Grande de Patillas and Rio Marin, in the municipality of Patillas in southern Puerto Rico, about 3 kilometers north of the town of Patillas and about 8 kilometers northeast of the town of Arroyo (fig. 1). The dam is owned and operated by the Puerto Rico Electric Power Authority (PREPA) and was constructed in 1914 for the irrigation of croplands in the southern coastal plains of Puerto Rico along the towns of Arroyo, Guayama, Patillas, and Salinas. Irrigation releases are made through the outlet works into the Patillas Irrigation Canal that extends 32.2 kilometers from the Patillas dam to Rio Salinas. The dam is a semi-hydraulic earthfill with a structural height of 44.80 meters, a top width of 4.57 meters, a base width of 190.49 meters, and a crest length of 325.21 meters. The spillway structure is physically separated from the earthfill dam, has an elevation of 58.21 meters above mean sea level, and has three radial arm gates (Puerto Rico Electric Power Authority, 1979). The reservoir impounds the waters of the Rio Grande de Patillas and Rio Marin. The reservoir has a drainage area of 66.3 square kilometers. Additional information and operational procedures are listed in Soler-Lopez and others (1999). During March 14-15, 2007, the U.S. Geological Survey (USGS), Caribbean Water Science Center (CWSC), in cooperation with the PREPA conducted a bathymetric survey of Lago Patillas to update the reservoir storage capacity and update the reservoir sedimentation rate by comparing the 2007 bathymetric survey data with previous 1997 data. The purpose of this report is to update the reservoir storage capacity, sedimentation rates, and areas of substantial sediment accumulation since April 1997.

Lago Patillas;Puerto Rico↗
USGS2011

A tunnel runs through it — An inside view of the Tualatin Mountains, Oregon

The Tualatin Mountains form a northwest-striking ridge about 350 m high that separates Portland, Oregon, from the cities of the Tualatin Valley to the west. Known informally as the Portland Hills, the ridge is a late Cenozoic anticline, bounded by reverse faults that dip toward the anticlinal axis. The anticline is a broad, open fold consisting chiefly of Miocene Columbia River Basalt Group, with remnants of Miocene-Pliocene Troutdale Formation and Pleistocene basalt of the Boring Volcanic Field on the flanks of the anticline. Anticlinal structures similar to the Tualatin Mountains are characteristic of the northern Willamette Valley, where the structures accommodate margin-parallel shortening of the Cascadia fore arc. Global Positioning System (GPS) results indicate that the shortening is due to the northward motion of Oregon at several millimeters per year with respect to stable North America. Some of the uplifts may contain active faults, but the structures are poorly exposed and are overlain by thick Pleistocene loess and Missoula flood deposits. Between 1993 and 1998, construction of the 3-mile-long (4500-m-long) TriMet MAX Light Rail tunnel through the Tualatin Mountains provided an unusual opportunity to investigate the geological structure and history of the Tualatin Mountains. This report is a collaborative effort among the tunnel geologists and the U.S. Geological Survey (USGS) to document the geologic story and quantify late Cenozoic and Quaternary deformation rates of the Tualatin Mountains.

Oregon↗
USGS2011

Terrestrial essential climate variables (ECVs) at a glance

The Global Terrestrial Observing System, Global Climate Observing System, World Meteorological Organization, and Committee on Earth Observation Satellites all support consistent global land observations and measurements. To accomplish this goal, the Global Terrestrial Observing System defined 'essential climate variables' as measurements of atmosphere, oceans, and land that are technically and economically feasible for systematic observation and that are needed to meet the United Nations Framework Convention on Climate Change and requirements of the Intergovernmental Panel on Climate Change. The following are the climate variables defined by the Global Terrestrial Observing System that relate to terrestrial measurements. Several of them are currently measured most appropriately by in-place observations, whereas others are suitable for measurement by remote sensing technologies. The U.S. Geological Survey is the steward of the Landsat archive, satellite imagery collected from 1972 to the present, that provides a potential basis for deriving long-term, global-scale, accurate, timely and consistent measurements of many of these essential climate variables.

Scientific Investigations Map↗
USGS2011

Land area change in coastal Louisiana from 1932 to 2010

Coastal Louisiana wetlands make up the seventh largest delta on Earth, contain about 37 percent of the estuarine herbaceous marshes in the conterminous United States, and support the largest commercial fishery in the lower 48 States. These wetlands are in peril because Louisiana currently undergoes about 90 percent of the total coastal wetland loss in the continental United States. Documenting and understanding the occurrence and rates of wetland loss are necessary for effective planning, protection, and restoration activities. The analyses of landscape change presented in this report use historical surveys, aerial data, and satellite data to track landscape changes. Summary data are presented for 1932-2010; trend data are presented for 1985-2010. These later data were calculated separately because of concerns over the comparability of the 1932 and 1956 datasets (which are based on survey and aerial data, respectively) with the later datasets (which are all based on satellite imagery). These analyses show that coastal Louisiana has undergone a net change in land area of about -1,883 square miles (mi 2 ) from 1932 to 2010. This net change in land area amounts to a decrease of about 25 percent of the 1932 land area. Persistent losses account for 95 percent of this land area decrease; the remainder are areas that have converted to water but have not yet exhibited the persistence necessary to be classified as "loss." Trend analyses from 1985 to 2010 show a wetland loss rate of 16.57 mi 2 per year. If this loss were to occur at a constant rate, it would equate to Louisiana losing an area the size of one football field per hour. The use of 17 datasets plus the application of consistent change criteria in this study provide opportunities to better understand the timing and causal mechanisms of wetland loss that are critical for forecasting landscape changes in the future.

Louisiana↗
USGS2012

Geologic cross section C-C' through the Appalachian basin from Erie County, north-central Ohio, to the Valley and Ridge province, Bedford County, south-central Pennsylvania

Geologic cross section C-C' is the third in a series of cross sections constructed by the U.S. Geological Survey (USGS) to document and improve understanding of the geologic framework and petroleum systems of the Appalachian basin. Cross section C-C' provides a regional view of the structural and stratigraphic framework of the Appalachian basin from north-central Ohio to the Valley and Ridge province in south-central Pennsylvania, a distance of approximately 260 miles (mi). This cross section is a companion to cross sections E-E' and D-D' that are located about 50 to 125 mi and 25 to 50 mi, respectively, to the southwest. Cross section C-C' contains much information that is useful for evaluating energy resources in the Appalachian basin. Although specific petroleum systems are not identified on the cross section, many of their key elements (such as source rocks, reservoir rocks, seals, and traps) can be inferred from lithologic units, unconformities, and geologic structures shown on the cross section. Other aspects of petroleum systems (such as the timing of petroleum generation and preferred migration pathways) may be evaluated by burial history, thermal history, and fluid flow models based on what is shown on the cross section. Cross section C-C' also provides a general framework (stratigraphic units and general rock types) for the coal-bearing section, although the cross section lacks the detail to illustrate key elements of coal systems (such as paleoclimate, coal quality, and coal rank). In addition, cross section C-C' may be used as a reconnaissance tool to identify plausible geologic structures and strata for the subsurface storage of liquid waste or for the sequestration of carbon dioxide.

Kentucky;Maryl;Ohio;Pennsylvania;Tennessee;Virgini↗
USGS2011

Water-level surface in the Chicot equivalent aquifer system in southeastern Louisiana, 2009

The Chicot equivalent aquifer system is an important source of freshwater in southeastern Louisiana. In 2005, about 47 million gallons per day (Mgal/d) were withdrawn from the Chicot equivalent aquifer system in East Baton Rouge, East Feliciana, Livingston, Tangipahoa, St. Helena, St. Tammany, Washington, and West Feliciana Parishes. Concentrated withdrawals exceeded 5 Mgal/d in Bogalusa, the city of Baton Rouge, and in northwestern East Baton Rouge Parish. In the study area, about 30,000 wells screened in the Chicot equivalent aquifer system were registered with the Louisiana Department of Transportation and Development (LaDOTD). These wells were constructed for public-supply, industry, irrigation, and domestic uses. Most of the wells were registered as domestic-use wells and are small-diameter, low-yielding wells. Total withdrawal from the Chicot equivalent aquifer system for domestic use was estimated to be 12 Mgal/d in 2005. This report documents the 2009 water-level surface of the Chicot equivalent aquifer system in southeastern Louisiana. The report also shows differences in water-level measurements for the years 1991 and 2009 at selected sites. Understanding changes and trends in water levels is important for continued use, planning, and management of groundwater resources. The U.S. Geological Survey, in cooperation with the Louisiana Department of Transportation and Development, conducted this study of the water-level surface of the Chicot equivalent aquifer system as part of an ongoing effort to monitor groundwater levels in aquifers in Louisiana.

Louisiana↗
USGS2011

Biostratigraphic data from Upper Cretaceous formations-eastern Wyoming, central Colorado, and northeastern New Mexico

Lithological and paleontological studies of outcrops of Upper Cretaceous formations were conducted at 12 localities in eastern Wyoming, central Colorado, and northeastern New Mexico. The sequence extends upward from the top of the Mowry Shale, or age-equivalent rocks, through the Graneros Shale, Greenhorn Limestone, Carlile Shale, Niobrara Formation, Pierre Shale, and Fox Hills Sandstone, or age-equivalent formations, to the top of the Laramie Formation, or laterally equivalent formations. The strata are mainly siliciclastic and calcareous, with thicknesses ranging from about 3,300 ft in northeastern New Mexico to as much as 13,500 ft in eastern Wyoming. Deposition was mainly in marine environments and molluscan fossils of Cenomanian through Maastrichtian ages are common. Radiometric ages were determined from beds of bentonite that are associated with fossil zones. The Upper Cretaceous formations at the 12 study localities are herein divided into three informal time-stratigraphic units based on fossil content and contact relations with adjacent strata. The basal unit in most places extends from the base of the Graneros to the top of the Niobrara, generally to the horizon of the fossil Scaphites hippocrepis, and spans a period of about 14 million years. The middle unit generally extends from the top of the Niobrara to the approximate middle of the Pierre, the horizon of the fossil Baculites gregoryensis, and represents a period of about 5 million years. The upper unit includes strata between the middle of the Pierre and the top of the Upper Cretaceous Series, which is the top of the Laramie Formation or of laterally equivalent formations; it represents a period of deposition of as much as 11 million years. Comparisons of the collections of fossils from each outcrop with the complete sequence of Upper Cretaceous index fossils can indicate disconformable contacts and lacunae. Widespread disconformities have been found within the Carlile Shale and between the Carlile Shale and the Niobrara Formation. Less extensive disconformities are within the Greenhorn Formation, the Niobrara Formation, and the Pierre Shale.

Scientific Investigations Map↗
USGS2014

Sedimentation survey of Lago Dos Bocas, Utuado, Puerto Rico, January 2010

Lago Dos Bocas reservoir was completed in 1942 to provide water for hydroelectric power generation along the northern coast of Puerto Rico. The reservoir had an original storage capacity of 37.50 million cubic meters (Mm3). The dam is located about 9 kilometers (km) northeast of the town of Utuado, immediately downstream of the original confluence of the Río Grande de Arecibo and the Río Caonillas (fig. 1). The Puerto Rico Electric Power Authority (PREPA) owns and operates the Lago Dos Bocas reservoir, and since 1996, the reservoir has become an essential part of the Puerto Rico Aqueduct and Sewer Authority (PRASA) North Coast Superaqueduct Project. The Superaqueduct is supplied by controlled releases for hydroelectric power generation that replenish the public-supply raw-water intake pool located about 10 km downstream from the Lago Dos Bocas Dam (fig. 1). As of 2005, the Superaqueduct supplies about 4.03 cubic meters per second (m 3 /s) (348,192 cubic meters per day [m 3 /d]) of potable water to communities along the northern coast, from Arecibo to the San Juan metropolitan area. Because of the importance of the reservoir to the North Coast Superaqueduct, the U.S. Geological Survey (USGS), in cooperation with PRASA, conducted a sedimentation survey of Lago Dos Bocas in January 2009. The results of this survey were used to estimate the useful life and the firm yield of the reservoir, and evaluate the need to dredge the reservoir.

Puerto Rico↗
USGS2012

Storage capacity and sedimentation trends of Lago Garzas, Puerto Rico, 1996-2007

Lago Garzas is located in west-central Puerto Rico, about 3.5 kilometers southwest of the town of Adjuntas, in the confluence of the Río Vacas and three other unnamed tributaries (fig. 1). The dam is owned and operated by the Puerto Rico Electric Power Authority (PREPA), and was constructed in 1943 for hydroelectric power generation and municipal water use along the southern coast. The dam is a semi-hydraulic earthfill embankment lined with boulders, and has a height of 61.57 meters, a top width of 9.14 meters, a base width of 365.76 meters, and a crest length of 227.37 meters; State Road PR-518 crosses the top of the dam. A morning-glory-type spillway is located near the west abutment of the dam at an elevation of 736.12 meters above mean sea level (Puerto Rico Water Resources Authority, 1969). Figure 2 shows an aerial photograph of the Lago Garzas earthfill dam and the morning-glory spillway section. Additional information and operational procedures are provided in Soler-López and others (1999). During July 17-18, 2007, the U.S. Geological Survey (USGS) Caribbean Water Science Center, in cooperation with the Puerto Rico Aqueduct and Sewer Authority, conducted a bathymetric survey of Lago Garzas to update the reservoir storage capacity and update the reservoir sedimentation rate by comparing the 2007 data with the previous 1996 bathymetric survey results. The purpose of this report is to describe and document the USGS sedimentation survey conducted at Lago Garzas during July 2007, including the methods used to update the reservoir storage capacity, sedimentation rates, and areas of substantial sediment accumulation since 1996.

Lago Garzas Basin Area↗
USGS2014

Sedimentation survey of Lago Loíza, Trujillo Alto, Puerto Rico, July 2009

Lago Loíza is a reservoir formed at the confluence of Río Gurabo and Río Grande de Loíza in the municipality of Trujillo Alto in central Puerto Rico, about 10 kilometers (km) north of the town of Caguas, about 9 km northwest of Gurabo, and about 3 km south of Trujillo Alto (fig. 1). The Carraizo Dam is owned and operated by the Puerto Rico Aqueduct and Sewer Authority (PRASA), and was constructed in 1953 as a water-supply reservoir for the San Juan Metropolitan area. The dam is a concrete gravity structure that is located in a shallow valley and has a gently sloping left abutment and steep right abutment. Non-overflow sections flank the spillway section. Waterways include an intake structure for the pumping station and power plant, sluiceways, a trash sluice, and a spillway. The reservoir was built to provide a storage capacity of 26.8 million cubic meters (Mm 3 ) of water at the maximum pool elevation of 41.14 meters (m) above mean sea level (msl) for the Sergio Cuevas Filtration Plant that serves the San Juan metropolitan area. The reservoir has a drainage area of 538 square kilometers (km 2 ) and receives an annual mean rainfall that ranges from 1,600 to 5,000 millimeters per year (mm/yr). The principal streams that drain into Lago Loíza are the Río Grande de Loíza, Río Gurabo, and Río Cañas. Two other rivers, the Río Bairoa and Río Cagüitas, discharge into the Río Grande de Loíza just before it enters the reservoir. The combined mean annual runoff of the Río Grande de Loíza and the Río Gurabo for the 1960–2009 period of record is 323 Mm 3 . Flow from these streams constitutes about 89 percent of the total mean annual inflow of 364 Mm 3 to the reservoir (U.S. Geological Survey, 2009). Detailed information about Lago Loíza reservoir structures, historical sediment accumulation, and a dredge conducted in 1999 are available in Soler-López and Gómez-Gómez (2005). During July 8–15, 2009, the U.S. Geological Survey (USGS) Caribbean Water Science Center (CWSC), in cooperation with PRASA, conducted a bathymetric survey of Lago Loíza to update the reservoir storage capacity and estimate the reservoir sedimentation rate by comparing the 2009 data with the previous 2004 bathymetric survey data. The purpose of this report is to document the methods used to update and present the results of the reservoir storage capacity, sedimentation rates, and areas of substantial sediment accumulation since 2004.

Puerto Rico↗