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At least 469 records · Page 26Linked to original sources
USGS2007

Flood of June 22-24, 2006, in North-Central Ohio, With Emphasis on the Cuyahoga River Near Independence

Heavy rains caused severe flooding on June 22-24, 2006, and damaged approximately 4,580 homes and 48 businesses in Cuyahoga County. Damage estimates in Cuyahoga County for the two days of flooding exceed $47 million; statewide damage estimates exceed $150 million. Six counties (Cuyahoga, Erie, Huron, Lucas, Sandusky, and Stark) in northeast Ohio were declared Federal disaster areas. One death, in Lorain County, was attributed to the flooding. The peak streamflow of 25,400 cubic feet per second and corresponding peak gage height of 23.29 feet were the highest recorded at the U.S. Geological Survey (USGS) streamflow-gaging station Cuyahoga River at Independence (04208000) since the gaging station began operation in 1922, exceeding the previous peak streamflow of 24,800 cubic feet per second that occurred on January 22, 1959. An indirect calculation of the peak streamflow was made by use of a step-backwater model because all roads leading to the gaging station were inundated during the flood and field crews could not reach the station to make a direct measurement. Because of a statistically significant and persistent positive trend in the annual-peak-streamflow time series for the Cuyahoga River at Independence, a method was developed and applied to detrend the annual-peak-streamflow time series prior to the traditional log-Pearson Type III flood-frequency analysis. Based on this analysis, the recurrence interval of the computed peak streamflow was estimated to be slightly less than 100 years. Peak-gage-height data, peak-streamflow data, and recurrence-interval estimates for the June 22-24, 2006, flood are tabulated for the Cuyahoga River at Independence and 10 other USGS gaging stations in north-central Ohio. Because flooding along the Cuyahoga River near Independence and Valley View was particularly severe, a study was done to document the peak water-surface profile during the flood from approximately 2 miles downstream from the USGS streamflow-gaging station at Independence to approximately 2 miles upstream from the gaging station. High-water marks were identified and flagged in the field. Third-order-accuracy surveys were used to determine elevations of the high-water marks, and the data were tabulated and plotted.

Scientific Investigations Report↗
USGS2008

The Role of Eolian Sediment in the Preservation of Archeologic Sites Along the Colorado River Corridor in Grand Canyon National Park, Arizona

Since the closure of Glen Canyon Dam in 1963, the natural hydrologic and sedimentary systems along the Colorado River in the Grand Canyon reach have changed substantially (see, for example, Andrews, 1986; Johnson and Carothers, 1987; Webb and others, 1999b; Rubin and others, 2002; Topping and others, 2003; Wright and others, 2005; Hazel and others, 2006b). The dam has reduced the fluvial sediment supply at the upstream boundary of Grand Canyon National Park by about 95 percent. Regulation of river discharge by dam operations has important implications for the storage and redistribution of sediment in the Colorado River corridor. In the absence of floods, sediment is not deposited at elevations that regularly received sediment before dam closure. Riparian vegetation has colonized areas at lower elevations than in predam time when annual floods removed young vegetation (Turner and Karpiscak, 1980). Together, these factors have caused a systemwide decrease in the size and number of subaerially exposed fluvial sand deposits since the 1960s, punctuated by episodic aggradation during the exceptional high-flow intervals in 1983-84, 1996, and 2004 and by sediment input from occasional tributary floods (Beus and others, 1985; Schmidt and Graf, 1987; Kearsley and others, 1994; Hazel and others, 1999; Schmidt and others, 2004; Wright and others, 2005). When the Bureau of Reclamation sponsored the creation of the Glen Canyon Environmental Studies (GCES) research initiative in 1982, research objectives included physical and biologic resources, whereas the effects of dam operations on cultural resources were not addressed (Fairley and others, 1994; Fairley, 2003). In the early 1980s, it was widely believed that because few archeologic sites were preserved within the river's annual-flood zone, cultural features would not be greatly affected by dam operations. Recent studies, however, indicate that alterations in the flow and sediment load of the Colorado River by Glen Canyon Dam operations may affect archeologic sites within the river corridor, even above the annual flood limit (Hereford and others, 1993, Yeatts, 1996, 1997; Thompson and Potochnik, 2000; Draut and others, 2005). (The annual-flood zone is defined here by the mean annual predam flood of 2,410 m3/s; the 'predam flood limit', the highest elevation at which fluvial deposits are present locally, was approximately equivalent to a rare, major flood of 8,500 m3/s; Topping and others, 2003.) Of about 500 archeologic sites documented between Glen Canyon Dam and Separation Canyon (255 river miles), more than 330 are considered to be within the area of potential effect (APE) of dam operations (Fairley and others, 1994; Neal and others, 2000; Fairley, 2005). The APE was designated by the National Park Service (NPS) to include the area below the peak stage of the 1884 flood; though previously believed to have reached 8,490 m3/s, this flood was shown by Topping and others (2003) to have peaked at 5,940 m3/s. Archeologic research and monitoring in Grand Canyon National Park focus increasingly on the potential effects of Glen Canyon Dam operations on the landscape in which these sites exist. Many archeologic sites in or on sedimentary deposits are being eroded, owing to eolian deflation and gully incision (Leap and others, 2000; Neal and others, 2000; Fairley, 2003, 2005). Hereford and others (1993) first suggested that gully incision of sedimentary deposits, and the base level to which small drainage systems respond, were linked to dam operations; they hypothesized that pronounced arroyo incision, which occurs during rainfall runoff, was caused by lowering of the effective base level at the mouths of ephemeral drainages to meet the new postdam elevation of high-flow sediment deposition, about 3 to 4 m below the lowest predam alluvial terraces. Thompson and Potochnik (2000) modified that hypothesis to include the restorative effects of fluvial deposition in the mouths of gullies and ar

Professional Paper↗
USGS2015

Wind River subbasin restoration: Annual report of U.S. Geological Survey activities January 2014 through December 2014

Executive Summary The Wind River subbasin in southwest Washington State provides habitat for a population of wild Lower Columbia River steelhead Oncorhynchus mykiss , which are listed as threatened under the Endangered Species Act. No hatchery steelhead have been planted in the Wind River subbasin since 1994, and hatchery adults are estimated to be less than one percent of adults in any year (Thomas Buehrens, Washington Department of Fish and Wildlife, personal communication). Numerous restoration actions have been implemented in the subbasin, including the removal of Hemlock Dam on Trout Creek in 2009. We used Passive Integrated Transponder (PIT) tagging and a series of instream PIT-tag interrogation systems (PTIS) to investigate life-histories, populations, and efficacy of habitat restoration actions for these steelhead. Data from our study, and companion work by Washington Department of Fish and Wildlife (WDFW), will contribute to Bonneville Power Administration’s (BPA) Research Monitoring and Evaluation (RM&E) Program Strategy of Fish Population Status Monitoring ( www.cbfish.org/ProgramStrategy.mvc/ViewProgramStrategySummary/1 ), specifically the sub-strategies of: 1) Assessing the Status and Trends of Diversity of Natural Origin Fish Populations and to Uncertainties Research regarding differing life histories of a wild steelhead population, 2) Assessing the Status and Trend of Adult Natural Origin Fish Populations, and 3) Monitoring and Evaluating the Effectiveness of Tributary Habitat Actions Relative to Environmental, Physical, or Biological Performance Objectives. During summer 2014, we PIT-tagged steelhead parr in headwater areas of the Wind River subbasin to investigate life-history diversity, specifically to compare fate of those juvenile steelhead that move downstream prior to smolting with those that remain in their natal areas until smolting. A series of instream PTISs monitored movement of these fish. We added a new multi-antenna PTIS on Trout Creek and made improvements to two of our smaller tributary PTISs during 2014. Detections at the instream PTISs showed trends of parr emigration during summer and fall, in addition to the expected movement of parr and smolts in spring. Long-term monitoring of PIT-tagged fish will provide information on contribution of various life-history strategies to smolt production and adult returns, as well as helping to identify factors influencing parr movement. Movements of PIT-tagged adult steelhead were tracked with our instream PTISs. These data will contribute to a better understanding of timing and distribution of spawning by this population of wild steelhead within the Wind River subbasin. Additionally, these data have provided information on timing of adult movements to various parts of the watershed, which is allowing us to assess adult use of tributary watersheds within the Wind River subbasin. These data are contributing to evaluating steelhead response to the removal of Hemlock Dam from Trout Creek. Hemlock Dam, which was located at rkm 2.0 of Trout Creek, was removed in summer 2009 and had contributed to hydrologic impairment of Trout Creek and potentially caused some deterrent to upstream adult steelhead migration. Evaluating restoration efforts is of interest to many managers and agencies so that funding and time are allocated for best results. The evaluation of various life-histories of Lower Columbia River steelhead within the Wind River subbasin provides information to better track populations, and more effectively direct habitat restoration and water allocation planning. Increasingly detailed Viable Salmonid Population information (Crawford and Rumsey 2009), such as that provided by PIT-tagging and instream PTISs networks like those we build and operate in the Wind River subbasin, provide data to better inform policy and management, as life-history strategies and production bottlenecks are identified and understood.

Washington↗
USGS2007

Hydrogeologic Setting and Ground-Water Flow in the Leetown Area, West Virginia

The Leetown Science Center is a research facility operated by the U.S. Geological Survey that occupies approximately 455-acres near Kearneysville, Jefferson County, West Virginia. Aquatic and fish research conducted at the Center requires adequate supplies of high-quality, cold ground water. Three large springs and three production wells currently (in 2006) supply water to the Center. The recent construction of a second research facility (National Center for Cool and Cold Water Aquaculture) operated by the U.S. Department of Agriculture and co-located on Center property has placed additional demands on available water resources in the area. A three-dimensional steady-state finite-difference ground-water flow model was developed to simulate ground-water flow in the Leetown area and was used to assess the availability of ground water to sustain current and anticipated future demands. The model also was developed to test a conceptual model of ground-water flow in the complex karst aquifer system in the Leetown area. Due to the complexity of the karst aquifer system, a multidisciplinary research study was required to define the hydrogeologic setting. Geologic mapping, surface- and borehole-geophysical surveys, stream base-flow surveys, and aquifer tests were conducted to provide the hydrogeologic data necessary to develop and calibrate the model. It would not have been possible to develop a numerical model of the study area without the intensive data collection and methods developments components of the larger, more comprehensive hydrogeologic investigation. Results of geologic mapping and surface-geophysical surveys verified the presence of several prominent thrust faults and identified additional faults and other complex geologic structures (including overturned anticlines and synclines) in the area. These geologic structures are known to control ground-water flow in the region. Results of this study indicate that cross-strike faults and fracture zones are major avenues of ground-water flow. Prior to this investigation, the conceptual model of ground-water flow for the region focused primarily on bedding planes and strike-parallel faults and joints as controls on ground-water flow but did not recognize the importance of cross-strike faults and fracture zones that allow ground water to flow downgradient across or through less permeable geologic formations. Results of the ground-water flow simulation indicate that current operations at the Center do not substantially affect either streamflow (less than a 5-percent reduction in annual streamflow) or ground-water levels in the Leetown area under normal climatic conditions but potentially could have greater effects on streamflow during long-term drought (reduction in streamflow of approximately 14 percent). On the basis of simulation results, ground-water withdrawals based on the anticipated need for an additional 150 to 200 gal/min (gallons per minute) of water at the Center also would not seriously affect streamflow (less than 8 to 9 percent reduction in streamflow) or ground-water levels in the area during normal climatic conditions. During drought conditions, however, the effects of current ground-water withdrawals and anticipated additional withdrawals of 150 to 200 gal/min to augment existing supplies result in moderate to substantial declines in water levels of 0.5-1.2 feet (ft) in the vicinity of the Center's springs and production wells. Streamflow was predicted to be reduced locally by approximately 21 percent. Such withdrawals during a drought or prolonged period of below normal ground-water levels would result in substantial declines in the flow of the Center's springs and likely would not be sustainable for more than a few months. The drought simulated in this model was roughly equivalent to the more than 1-year drought that affected the region from November 1998 through February 2000. The potential reduction in streamflow is a result of capture of ground water tha

Scientific Investigations Report↗
USGS2023

Monitoring Avian Productivity and Survivorship (MAPS) 6-year summary, Naval Outlying Landing Field, Imperial Beach, southwestern San Diego County, California, 2014–20

Executive Summary From 2014 to 2020, a Monitoring Avian Productivity and Survivorship (MAPS) banding station (station) was operated at the Naval Outlying Landing Field (NOLF), Imperial Beach, in southwestern San Diego County, California. The station was established as part of a long-term monitoring program of Neotropical migratory bird populations on NOLF and helps Naval Base Coronado (NOLF is a component) meet the goals and objectives of the Department of Defense Partners in Flight program and the Birds and Migratory Birds Management Strategies of the Naval Base Coronado Integrated Natural Resources Management Plan. The station was established in 2009 and has been in operation during the spring and summer since 2009 except for 2016 when it was not funded. The station was operated by AMEC Earth and Environmental, Inc., from 2009 to 2011, by the U.S. Geological Survey from 2012 to 2015, the San Diego Natural History Museum in 2017, and the U.S. Geological Survey again from 2018 to 2023. This report synthesizes results from 2014 to 2020. A prior report presents summaries and analyses from 2009 to 2013. The banding station at NOLF was operated according to the standard MAPS protocol with some exceptions. Ten mist nets used to capture birds were erected in fixed locations that remained consistent between and within years, with few minor relocations. Nets were open for 6 hours per day, once every 10 days (a netting period) for 13 netting periods starting April 1 each year. Occasionally, poor weather conditions (for example, rain, wind, or excessive heat) prevented net operation or forced nets to be closed early (or, rarely, late). Nets were checked periodically throughout the day and birds were removed, processed (leg bands affixed, measurements recorded), and released. From 2014 to 2020, we had 3,543 captures (including initial captures and recaptures) of a maximum of 3,264 year-unique captures (543±143 year-unique captures [the total number of individual birds captured for the first time each year]). The count of year-unique captures included 2,702 newly banded birds, 258 individuals that were recaptured from previous years, and 304 birds that were released unbanded (218 hummingbirds and 86 other birds that were intentionally released unbanded [game birds, and so forth] or escaped before banding). Individuals of 68 species were captured, 39 of which breed at or in the immediate vicinity of the MAPS banding station. Bird capture rate averaged 43±30 captures per day (corrected to account for variation in effort) for all years (range 7–163 effort-corrected captures per day) and species richness per year averaged 43±4. Bushtit ( Psaltriparus minimus ) was the most abundant species captured, followed by Orange-crowned Warbler ( Leiothlypis celata ), Wilson’s Warbler ( Cardellina pusilla ), House Finch ( Haemorhous mexicanus ), Song Sparrow ( Melospiza melodia ), and Common Yellowthroat ( Geothlypis trichas ). The mean adult sex ratio of all species combined across all years was 54:46 male:female. Adults averaged 73±12 percent of known age captures per year (range 59–94 percent), and juveniles averaged 27±12 percent (range 6–41 percent). Nineteen sensitive species were detected at NOLF (12 captured and 7 observed only). During 2014–20, we captured one State and federally endangered species, Least Bell’s Vireo ( Vireo bellii pusillus ); one federally threatened species, California Gnatcatcher ( Polioptila californica ); one State endangered species, Willow Flycatcher ( Empidonax traillii ); and two State species of concern, Yellow-breasted Chat ( Icteria virens ) and Yellow Warbler ( Setophaga petechia ). One additional State species of concern, Northern Harrier ( Circus hudsonius ), was observed at the MAPS banding station but not captured. Peregrine Falcon ( Falco peregrinus ) and White-tailed Kite ( Elanus leucurus ), California State fully protected species, also were observed at the MAPS banding station. Seven federal bird species of conservation concern—Calliope Hummingbird ( Selasphorus calliope ), Rufous Hummingbird ( Selasphorus rufus ), Allen’s Hummingbird ( Selasphorus sasin ), Nuttall’s Woodpecker ( Dryobates nuttallii ), Wrentit ( Chamaea fasciata ), California Thrasher ( Toxostoma redivivum ), and Lawrence’s Goldfinch ( Spinus lawrencei )—also were captured, and four additional federal bird species of conservation concern—Willet ( Tringa semipalmata ), Western Gull ( Larus occidentalis ), California Gull ( Larus californicus ), and Bullock’s Oriole ( Icterus bullockii )—were observed but not captured. Local population trends varied among species and years. From 2012 to 2019, year-round residents Bushtit, Song Sparrow, and Common Yellowthroat significantly decreased, whereas the migrant Least Bell’s Vireo increased. The total number of captures for all species except Least Bell’s Vireo was lowest in 2017, corresponding to the habitat damage caused by Kuroshio shot hole borer beetle ( Euwallacea kuroshio ) in the Tijuana River Valley. Annual productivity and annual adult survival were calculated for seven breeding species based on criteria used by the Institute for Bird Populations (Least Bell’s Vireo, Bushtit, Wrentit, House Wren [ Troglodytes aedon ], Song Sparrow, Orange-crowned Warbler, and Common Yellowthroat). Productivity was highest for most species in 2010 and 2019, years with high precipitation, and lowest in 2014 and 2018, years with low precipitation. Song Sparrow demonstrated the highest productivity among species and Least Bell’s Vireo had the lowest productivity. Annual adult survival was generally high from 2011 to 2012 and from 2018 to 2019. Bushtit had higher annual survival with lower late winter precipitation. Either temperature or precipitation was associated with productivity for all species except Wrentit, and with survival for all species except Least Bell’s Vireo and Common Yellowthroat. For most species, productivity was positively associated with precipitation, and both productivity and survival were negatively associated with temperature. Other studies have found that higher temperatures led to increased predation by snakes and birds and also increased vector-borne disease transmission, such as West Nile virus. Predicted regional increases in temperature over the next 30 years will likely affect the demographics of these species. The Song Sparrow population increased with higher breeding productivity during the previous year, and the Bushtit population increased with higher annual survival and higher productivity during the previous year. Aside from a possible positive association between survivorship and Common Yellowthroat population growth, productivity and survival rates did not appear to influence population change for other focal species.

California↗
USGS2016

Suspended-sediment concentrations, bedload, particle sizes, surrogate measurements, and annual sediment loads for selected sites in the lower Minnesota River Basin, water years 2011 through 2016

Accurate measurements of fluvial sediment are important for assessing stream ecological health, calculating flood levels, computing sediment budgets, and managing and protecting water resources. Sediment-enriched rivers in Minnesota are a concern among Federal, State, and local governments because turbidity and sediment-laden waters are the leading impairments and affect more than 6,000 miles of rivers in Minnesota. The suspended sediment in the lower Minnesota River is deleterious, contributing about 75 to 90 percent of the suspended sediment being deposited into Lake Pepin. The Saint Paul District of the U.S. Army Corps of Engineers and the Lower Minnesota River Watershed District collaborate to maintain a navigation channel on the lower 14.7 miles of the Minnesota River through scheduled dredging operations. The Minnesota Pollution Control Agency has adopted a sediment-reduction strategy to reduce sediment in the Minnesota River by 90 percent by 2040. The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, the Minnesota Pollution Control Agency, and the Lower Minnesota River Watershed District, collected suspended-sediment, bedload, and particle-size samples at five sites in the lower Minnesota River Basin during water years 2011 through 2014 and surrogate measurements of acoustic backscatter at one of these sites on the lower Minnesota River during water years 2012 through 2016 to quantify sediment loads and improve understanding of sediment-transport relations. Annual sediment loads were computed for calendar years 2011 through 2014. Data collected from water years 2011 through 2014 indicated that two tributaries, Le Sueur River and High Island Creek, had the highest sediment yield and concentrations of suspended sediment. These tributaries also had greater stream gradients than the sites on the Minnesota River. Suspended fines were greater than suspended sand at all sites in the study area. The range of median particle sizes matched the range for stream gradients from greatest to smallest. Bedload ranged from 3 to 20 percent of the total load at the Le Sueur River, Minnesota River at Mankato, and High Island Creek and was less than 1 percent of the total load at the Minnesota River near Jordan and at Fort Snelling State Park. The reach of the Minnesota River between Mankato and Jordan is a major source of sediment, with the sediment yield at Jordan being two and a half times greater than at Mankato. Between Jordan and Fort Snelling, the sediment yield decreases substantially, which indicates that the Minnesota River in this reach is a sink for sediment. Surrogate measurements (acoustic backscatter) collected with suspended-sediment concentration data from water years 2012 through 2016 from the Minnesota River at Fort Snelling State Park indicated strong relations between the acoustic backscatter and suspended-sediment concentrations. These results point to the dynamic nature of sediment aggradation, degradation, and transport in the Minnesota River Basin. The analyses described in this report will improve the understanding of sediment-transport relations and sediment budgets in the Minnesota River Basin.

Minnesota↗
USGS2015

Monitoring avian productivity and survivorship (MAPS) 5-year summary, Naval Outlying Landing Field, Imperial Beach, southwestern San Diego County, California, 2009-13

During 2009–13, a Monitoring Avian Productivity and Survivorship (MAPS) banding station was operated at the Naval Outlying Landing Field (NOLF), Imperial Beach, in southwestern San Diego County, California. The station was established as part of a long-term monitoring program of Neotropical migratory bird populations on NOLF and helps Naval Base Coronado (NOLF is a component) meet the goals and objectives of Department of Defense Partners in Flight program and the Birds and Migratory Birds Management Strategies of the Naval Base Coronado Integrated Natural Resources Management Plan. During 2009–13, captures averaged 644 ±155 per year. Fifty-seven species were captured, of which 44 are Neotropical migratory species and 33 breed at the MAPS station. Twenty-two sensitive species were detected, including Least Bell’s Vireo ( Vireo bellii pusillus ), Willow Flycatcher ( Empidonax traillii ), Yellow-breasted Chat ( Icteria virens ) and Yellow Warbler ( Setophaga petechia ). Local population trends varied among species and years, as did annual productivity (number of young per adult). We found no significant relationship between productivity and the observed population size in the subsequent year for any species, nor did we find an association between productivity and precipitation for the current bio-year. Similarly, survivorship varied across species and years, and there was no obvious relationship between adult survivorship and observed population size for any species except Wrentit ( Chamaea fasciata ), for which the relationship was positive. Adult survivorship was unrelated to precipitation at the MAPS station. Additional years of data will be required to generate sample sizes adequate for more rigorous analyses of survivorship and productivity as predictors of population growth.

California↗
USGS2004

Regression equations for estimating flood flows for the 2-, 10-, 25-, 50-, 100-, and 500-Year recurrence intervals in Connecticut

Multiple linear-regression equations were developed to estimate the magnitudes of floods in Connecticut for recurrence intervals ranging from 2 to 500 years. The equations can be used for nonurban, unregulated stream sites in Connecticut with drainage areas ranging from about 2 to 715 square miles. Flood-frequency data and hydrologic characteristics from 70 streamflow-gaging stations and the upstream drainage basins were used to develop the equations. The hydrologic characteristics-drainage area, mean basin elevation, and 24-hour rainfall-are used in the equations to estimate the magnitude of floods. Average standard errors of prediction for the equations are 31.8, 32.7, 34.4, 35.9, 37.6 and 45.0 percent for the 2-, 10-, 25-, 50-, 100-, and 500-year recurrence intervals, respectively. Simplified equations using only one hydrologic characteristic-drainage area-also were developed. The regression analysis is based on generalized least-squares regression techniques. Observed flows (log-Pearson Type III analysis of the annual maximum flows) from five streamflow-gaging stations in urban basins in Connecticut were compared to flows estimated from national three-parameter and seven-parameter urban regression equations. The comparison shows that the three- and seven- parameter equations used in conjunction with the new statewide equations generally provide reasonable estimates of flood flows for urban sites in Connecticut, although a national urban flood-frequency study indicated that the three-parameter equations significantly underestimated flood flows in many regions of the country. Verification of the accuracy of the three-parameter or seven-parameter national regression equations using new data from Connecticut stations was beyond the scope of this study. A technique for calculating flood flows at streamflow-gaging stations using a weighted average also is described. Two estimates of flood flows - one estimate based on the log-Pearson Type III analyses of the annual maximum flows at the gaging station, and the other estimate from the regression equation - are weighted together based on the years of record at the gaging station and the equivalent years of record value determined from the regression. Weighted averages of flood flows for the 2-, 10-, 25-, 50-, 100-, and 500-year recurrence intervals are tabulated for the 70 streamflow-gaging stations used in the regression analysis. Generally, weighted averages give the most accurate estimate of flood flows at gaging stations. An evaluation of the Connecticut's streamflow-gaging network was performed to determine whether the spatial coverage and range of geographic and hydrologic conditions are adequately represented for transferring flood characteristics from gaged to ungaged sites. Fifty-one of 54 stations in the current (2004) network support one or more flood needs of federal, state, and local agencies. Twenty-five of 54 stations in the current network are considered high-priority stations by the U.S. Geological Survey because of their contribution to the longterm understanding of floods, and their application for regionalflood analysis. Enhancements to the network to improve overall effectiveness for regionalization can be made by increasing the spatial coverage of gaging stations, establishing stations in regions of the state that are not well-represented, and adding stations in basins with drainage area sizes not represented. Additionally, the usefulness of the network for characterizing floods can be maintained and improved by continuing operation at the current stations because flood flows can be more accurately estimated at stations with continuous, long-term record.

Connecticut↗
USGS2011

Hydrogeologic framework and hydrologic budget components of the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho

The Columbia Plateau Regional Aquifer System (CPRAS) covers an area of about 44,000 square miles in a structural and topographic basin within the drainage of the Columbia River in Washington, Oregon, and Idaho. The primary aquifers are basalts of the Columbia River Basalt Group (CRBG) and overlying sediment. Eighty percent of the groundwater use in the study area is for irrigation, in support of a $6 billion per year agricultural economy. Water-resources issues in the Columbia Plateau include competing agricultural, domestic, and environmental demands. Groundwater levels were measured in 470 wells in 1984 and 2009; water levels declined in 83 percent of the wells, and declines greater than 25 feet were measured in 29 percent of the wells. Conceptually, the system is a series of productive basalt aquifers consisting of permeable interflow zones separated by less permeable flow interiors; in places, sedimentary aquifers overly the basalts. The aquifer system of the CPRAS includes seven hydrogeologic units-the overburden aquifer, three aquifer units in the permeable basalt rock, two confining units, and a basement confining unit. The overburden aquifer includes alluvial and colluvial valley-fill deposits; the three basalt units are the Saddle Mountains, Wanapum, and Grande Ronde Basalts and their intercalated sediments. The confining units are equivalent to the Saddle Mountains-Wanapum and Wanapum-Grande Ronde interbeds, referred to in this study as the Mabton and Vantage Interbeds, respectively. The basement confining unit, referred to as Older Bedrock, consists of pre-CRBG rocks that generally have much lower permeabilities than the basalts and are considered the base of the regional flow system. Based on specific-capacity data, median horizontal hydraulic conductivity (Kh) values for the overburden, basalt units, and bedrock are 161, 70, and 6 feet per day, respectively. Analysis of oxygen isotopes in water and carbon isotopes in dissolved inorganic carbon from groundwater samples indicates that groundwater in the CPRAS ranges in age from modern (<50 years) to Pleistocene (>10,000 years). The oldest groundwater resides in deep, downgradient locations indicating that groundwater movement and replenishment in parts of this regional aquifer system have operated on long timescales under past natural conditions, which is consistent with the length and depth of long flow paths in the system. The mean annual recharge from infiltration of precipitation for the 23-year period 1985-2007 was estimated to be 4.6 inches per year (14,980 cubic feet per second) using a polynomial regression equation based on annual precipitation and the results of recharge modeling done in the 1980s. A regional-scale hydrologic budget was developed using a monthly SOil WATer (SOWAT) Balance model to estimate irrigation-water demand, groundwater flux (recharge or discharge), direct runoff, and soil moisture within irrigated areas. Mean monthly irrigation throughout the study area peaks in July at 1.6 million acre-feet (MAF), of which 0.45 and 1.15 MAF are from groundwater and surface-water sources, respectively. Annual irrigation water use in the study area averaged 5.3 MAF during the period 1985-2007, with 1.4 MAF (or 26 percent) supplied from groundwater and 3.9 MAF supplied from surface water. Mean annual recharge from irrigation return flow in the study area was 4.2 MAF (1985-2007) with 2.1 MAF (50 percent) occurring within the predominately surface-water irrigated regions of the study area. Annual groundwater-use estimates were made for public supply, self-supplied domestic, industrial, and other uses for the period 1984 through 2009. Public supply groundwater use within the study area increased from 200,600 acre-feet per year (acre-ft/yr) in 1984 to 269,100 acre-ft/yr in 2009. Domestic self-supplied groundwater use increased from 54,580 acre-ft/yr in 1984 to 71,160 acre-ft/yr in 2009. Industrial groundwater use decreased from 53,390 acre-ft/yr in 1984 t

Scientific Investigations Report↗
USGS2015

Inverse modeling with RZWQM2 to predict water quality

This chapter presents guidelines for autocalibration of the Root Zone Water Quality Model (RZWQM2) by inverse modeling using PEST parameter estimation software ( Doherty, 2010 ). Two sites with diverse climate and management were considered for simulation of N losses by leaching and in drain flow: an almond [ Prunus dulcis (Mill.) D.A. Webb] orchard in the San Joaquin Valley, California and the Walnut Creek watershed in central Iowa, which is predominantly in corn ( Zea mays L.)–soybean [ Glycine max (L.) Merr.] rotation. Inverse modeling provides an objective statistical basis for calibration that involves simultaneous adjustment of model parameters and yields parameter confidence intervals and sensitivities. We describe operation of PEST in both parameter estimation and predictive analysis modes. The goal of parameter estimation is to identify a unique set of parameters that minimize a weighted least squares objective function, and the goal of predictive analysis is to construct a nonlinear confidence interval for a prediction of interest by finding a set of parameters that maximizes or minimizes the prediction while maintaining the model in a calibrated state. We also describe PEST utilities (PAR2PAR, TSPROC) for maintaining ordered relations among model parameters (e.g., soil root growth factor) and for post-processing of RZWQM2 outputs representing different cropping practices at the Iowa site. Inverse modeling provided reasonable fits to observed water and N fluxes and directly benefitted the modeling through: (i) simultaneous adjustment of multiple parameters versus one-at-a-time adjustment in manual approaches; (ii) clear indication by convergence criteria of when calibration is complete; (iii) straightforward detection of nonunique and insensitive parameters, which can affect the stability of PEST and RZWQM2; and (iv) generation of confidence intervals for uncertainty analysis of parameters and model predictions. Composite scaled sensitivities, which reflect the total information provided by the observations for a parameter, indicated that most of the RZWQM2 parameters at the California study site (CA) and Iowa study site (IA) could be reliably estimated by regression. Correlations obtained in the CA case indicated that all model parameters could be uniquely estimated by inverse modeling. Although water content at field capacity was highly correlated with bulk density (−0.94), the correlation is less than the threshold for nonuniqueness (0.95, absolute value basis). Additionally, we used truncated singular value decomposition (SVD) at CA to mitigate potential problems with highly correlated and insensitive parameters. Singular value decomposition estimates linear combinations (eigenvectors) of the original process-model parameters. Parameter confidence intervals (CIs) at CA indicated that parameters were reliably estimated with the possible exception of an organic pool transfer coefficient (R45), which had a comparatively wide CI. However, the 95% confidence interval for R45 (0.03–0.35) is mostly within the range of values reported for this parameter. Predictive analysis at CA generated confidence intervals that were compared with independently measured annual water flux (groundwater recharge) and median nitrate concentration in a collocated monitoring well as part of model evaluation. Both the observed recharge (42.3 cm yr −1 ) and nitrate concentration (24.3 mg L −1 ) were within their respective 90% confidence intervals, indicating that overall model error was within acceptable limits.

Book chapter↗
USGS2014

Comparison of the U.S. lead recycling industry in 1998 and 2011

Since 1998, the structure of the lead recycling industry has changed and trade patterns of the domestic lead recycling industry have shifted. Although the domestic demand for lead has remained relatively constant since 1998, production of lead has increasingly shifted to the domestic secondary lead industry. The last primary lead smelter in the United States closed at the end of 2013, at which time the secondary lead industry became the sole source of domestic lead production. The amount of lead recovered annually from scrap batteries generally increased from about 900,000 metric tons in 1995 to more than 1,100,000 metric tons in 2012. The percentage of total U.S. lead production attributed to battery scrap increased from 65 percent in 1995 to 87 percent in 2012. Since the North American Free Trade Agreement took effect in 1994, trade patterns among the United States, Canada, and Mexico have changed for recycled lead products. In the late 1990s, the principal sources of lead waste and scrap not derived from batteries were Canada, Mexico, and South America; by 2011, the principal sources were Central America and Asia, with decreasing amounts from Canada and South America. Since 1998, the amount of lead derived from imported batteries and scrap from Canada has ranged from 50 to 90 percent, and the amount imported from Mexico has ranged from 3 to 20 percent. Canada received about 50 percent of the lead contained in spent lead-acid batteries and scrap exported from the United States in 1998, and Mexico received about 4 percent. By 2012, however, the amount of lead scrap exported to Canada had decreased to about 10 percent, and the amount of lead-based scrap products, primarily batteries, exported to Mexico from the United States had increased to 47 percent. Vertical integration of the domestic secondary lead industry and higher costs required to implement more stringent ambient air standards in the United States have led some companies to shift lead recycling operations to Mexico. U.S. secondary lead producers are increasingly competing with Canadian and Mexican facilities for market share.

Scientific Investigations Report↗
USGS2006

Relations of Water Quality to Streamflow, Season, and Land Use for Four Tributaries to the Toms River, Ocean County, New Jersey, 1994-99

The effects of nonpoint-source contamination on the water quality of four tributaries to the Toms River in Ocean County, New Jersey, have been investigated in a 5-year study by the U.S. Geological Survey (USGS), in cooperation with the New Jersey Department of Environmental Protection (NJDEP). The purpose of the study was to relate the extent of land development to loads of nutrients and other contaminants to these streams, and ultimately to Barnegat Bay. Volumetric streamflow (discharge) was measured at 6 monitoring sites during 37 stormflow and base-flow sampling events over a 5-year period (May 1994-September 1999). Concentrations and yields (area-normalized instantaneous load values) of nitrogen and phosphorus species, total suspended solids, and fecal coliform bacteria were quantified, and pH, dissolved oxygen, and stream stage were monitored during base-flow conditions and storms. Sufficient data were collected to allow for a statistical evaluation of differences in water quality among streams in subbasins with high, medium, and low levels of land development. Long Swamp Creek, in a highly developed subbasin (64.2 percent developed); Wrangle Brook, in a moderately developed subbasin (34.5 percent); Davenport Branch, in a slightly developed subbasin (22.8 percent); and Jakes Branch, in an undeveloped subbasin (0 percent) are the subbasins selected for this study. No point-source discharges are known to be present on these streams. Water samples were collected and analyzed by the NJDEP, and discharge measurements and data analysis were conducted by the USGS. Total nitrogen concentrations were lower in Davenport Branch than in Long Swamp Creek and Wrangle Brook during base flow and stormflow. Concentrations of total nitrogen and nitrate were highest in Wrangle Brook (as high as 3.0 mg/L and 1.6 mg/L, respectively) as a result of high concentrations of nitrate in samples collected during base flow; nitrate loading from ground-water discharge is much higher in Wrangle Brook than in any of the other streams, possibly as a result of an experimental wastewater-(secondary effluent) disposal site that was in operation during the 1980's. Ammonia concentrations were higher in samples from Long Swamp Creek than in those from the other two monitoring sites under all flow conditions, and ammonia yields were higher during stormflow than base flow at all monitoring sites. Concentrations and yields of fecal coliform bacteria and total suspended solids were higher during stormflow than during base flow at all monitoring sites. Concentrations and yields were significantly higher in Long Swamp Creek, a highly developed subbasin and Wrangle Brook, a moderately developed subbasin than in Davenport Branch, a slightly developed subbasin. Concentrations and yields of phosphate species, which also are strongly related to stormflow, were higher during stormflow in Long Swamp Creek than in the other subbasins. Base-flow separation techniques were used on hydrographs generated for storms to distinguish the fraction of discharge and constituent loading attributable to storm runoff (overland flow) from the fraction contributed by ground-water discharge. Precipitation records were used to determine the total annual volumes of ground-water discharge and runoff at each monitoring site. These volumes were used in conjunction with water-quality data to calculate total annual loads of each constituent at each monitoring site, separated into ground-water discharge and runoff fractions. It was determined that loads of ammonia, nitrate, organic nitrogen, total nitrogen, and orthophosphate in ground-water discharge were significantly higher in the moderately developed Wrangle Brook subbasin than in the highly developed Long Swamp Creek subbasin, and that no relation was apparent between the percent of land development and constituent loads from ground-water discharge. The loading of each constituent contributed by ground-water discharge is specific

Scientific Investigations Report↗
USGS2019

Potentiometric surface of the Mississippi River Valley alluvial aquifer, spring 2016

A potentiometric surface map for spring 2016 was created for the Mississippi River Valley alluvial (MRVA) aquifer using selected available groundwater-altitude data from wells and surface-water-altitude data from streamgages. Most of the wells were measured annually or one time after installation, but some wells were measured more than one time or continually; streamgages are typically operated continuously. Personnel from the Arkansas Natural Resources Commission, Arkansas Department of Health, Arkansas Geological Survey, Illinois Department of Agriculture, Illinois State Water Survey, Louisiana Department of Natural Resources, Louisiana Department of Transportation and Development, Mississippi Department of Environmental Quality, Yazoo Mississippi Delta Joint Water Management District, U.S. Department of Agriculture–Natural Resources Conservation Service, and the U.S. Geological Survey (USGS) routinely collect groundwater data from wells screened in the MRVA aquifer. The USGS and the U.S. Army Corps of Engineers routinely collect data on river stage and discharge for the rivers overlying the MRVA aquifer. The potentiometric surface map for 2016 was created using existing data as part of the USGS Water Availability and Use Science Program to support investigations that characterize the MRVA aquifer. Sufficient groundwater-altitude data were available to create a potentiometric-surface map for spring 2016 for about 81 percent of the aquifer area. The potentiometric contours ranged from 10 to 340 feet. The regional direction of groundwater flow in the MRVA aquifer was generally towards the south-southwest, except in areas of groundwater-altitude depressions, where groundwater flows into the depressions, and near rivers, where groundwater flow generally parallels the flow in the rivers. There are large depressions in the potentiometric surface of the MRVA aquifer in the lower half of the Cache region and in most of the Grand Prairie and Delta regions.

Arkansas, Illinois, Kentucky, Louisiana, Mississip↗
USGS2024

Dam removal cost databases and drivers

The United States (U.S.) has over 90,000 dams listed in the National Inventory of Dams that provide vital infrastructure to support water management for municipal and industrial uses including irrigation, hydropower, flood control, navigation, recreation, and habitat, among other uses (NID 2023). The Bureau of Reclamation (Reclamation) and U.S. Army Corps of Engineers (USACE) operate and maintain approximately 489 and 740 dams, respectively, as well as associated structures which provide flood risk management, navigation, water supply, hydropower, environmental stewardship, fish and wildlife conservation, and recreation benefits. As dams age, structural and operational maintenance investments increase until a time when decisions on whether to rehabilitate, replace, or decommission the dam need to be made. While most dams continue to provide important value even with maintenance requirements, at least 2,000 dams have been removed in the U.S. during the past 110 years, with an upward trend in the last few decades (American Rivers 2023). Decommissioning a dam may be considered when the purpose of the dam is no longer needed or other factors such as dam safety, fish passage, recreation safety, or river restoration goals take higher priority and are more economically feasible for the dam owner long-term. Dam safety programs, river restoration programs, and asset class management programs need cost estimating methods to consider dam decommissioning when appropriate. Traditional cost estimating approaches in planning stages focus mainly on dam removal construction and may leave out or have uncertainty on important complexities that can have substantial effects on total costs and be critical for project success. As the numbers of dam removal case studies increase, a growing set of cost data has become available (Duda et al. 2023a; Tullos and Bountry 2023; American Rivers 2022). However, total costs vary over five orders of magnitude for similar size dams, and it was unclear why. We evaluated three sets of cost data that had varying level of details regarding elements contributing to dam removal costs reported by project managers working on the dam removal studies and construction means and methods. We created planning-level cost estimating tools to assist with projects needing to consider the dam removal alternative: (1) new databases of case studies (Duda et al. 2023a; Tullos and Bountry 2023); (2) scoping questions to help determine if complexity cost drivers will be present; (3) machine learning based regression trees to estimate a potential cost range; and (4) a Computation Guide for Cost Estimating that can be used to inform discussions on potential dam removal cost items, quantities, and unit costs (appendix A). The collected data showed that dam height is important but is not a reliable predictor of the removal cost without considering other elements. However, knowing some basic characteristics about the average annual flow and geographic location of the dam site, in addition to dam size, can improve the ability to use past case studies for planning-level cost estimating. By additionally incorporating scoping questions related to sediment removal, mitigation, or other infrastructure, the likelihood of complexity cost drivers and the initial uncertainty of a cost estimate can be further reduced especially for small dams. Applying the Computation Guide for Cost Estimating requires more robust information but helps users reduce cost uncertainty. This step further refines the dam removal objective, removal approach (partial or full; phased or instantaneous), engineering design, construction means and methods, quantities, and unit costs, and results in a quantitative cost estimate.

Final Report↗
USGS2023

Critical minerals in subduction-related magmatic-hydrothermal systems of the United States

During the World War and Cold War eras (1910s–1990s), domestic consumption of numerous mineral commodities relied increasingly on imported supplies. Consumption reliance has since expanded to include 50 “critical minerals” (elements and mineral commodities) that are mostly to entirely imported and subject to curtailment by suppliers or supply chain disruption. New domestic supplies of critical minerals are being pursued by mining companies and by several federal departments and agencies. Information on domestic deposits and resources of critical minerals is being compiled by the U.S. Geological Survey Mineral Resources Program, which has organized investigations by mineral system, deposit type, and commodity. Production, reserves, resources, and inventories of 21 critical minerals in domestic magmatic-hydrothermal deposits related to subduction-generated magmatism, and in tailings, slag, slimes, and electrolyte from copper concentrators, smelters, and refineries that processed some deposits, are largely restricted to Western States and Alaska. The critical mineral commodities Al, Sb, As, Bi, Co, fluorite, Ga, Ge, In, Mn, Ni, Nb, Pd, Pt, potash, Re, Ta, Te, Sn, W, and V are variably concentrated in porphyry/skarn copper-(molybdenum), skarn-replacement-vein (S-R-V) tungsten, polymetallic sulfide S-R-V intermediate sulfidation (IS), high-sulfidation gold-silver, low-sulfidation gold-silver, and lithocap alunite deposit types. These deposit types occur in porphyry copper-molybdenum-gold, alkalic porphyry, porphyry tin (granite related), and reduced intrusion-related mineral systems. Production, reserves, and resources of Co, Ni, Nb, Pd, Pt, Ta, Sn, and V in subduction-related deposits in Western States are insignificant to small, mostly equivalent to months to a few years of recent annual domestic consumption (2016–2020). Significant inventories, equivalent to 2 or more years of consumption of aluminum, antimony, potash, and tungsten in unmined S-R-V tungsten, polymetallic sulfide S-R-V-IS, and lithocap alunite deposits vary from approximately 2 to 8 years. Several decades of consumption of arsenic, bismuth, fluorite, gallium, germanium, and indium exist in some polymetallic sulfide S-R-V-IS and lithocap alunite deposit types. Based on concentrations of critical minerals in reserves, resources, drill holes, and deposit domains (ore types), and in captive refinery records, the largest domestic inventories of Sb, As, Bi, Re, and Te, and possibly Ga, Ge, In, Sn, and W, are in porphyry copper-molybdenum (Cu-Mo) deposits in Alaska, Idaho, Utah, and Arizona, and in interim products of processing porphyry Cu-Mo deposit ores for recovery of copper and molybdenum. Concentrations of critical minerals in archival specimens and sample collections, although somewhat biased by collection and conservation decisions and categorization, are broadly proportionate to those in reserves, resources, and drill holes. These concentrations imply significant inventories of some critical minerals in deposits for which production, resources, and refinery records are unavailable or incomplete. Because of the large masses of ores mined and processed annually (hundreds of millions of metric tons) and in reserves and resources (hundreds of millions of metric tons to billions of metric tons), calculated inventories of critical minerals in porphyry Cu-Mo deposits are equivalent to decades and centuries of recent consumption. However, these inventories should not be considered consumable supplies without reserve definition and development of economically viable mining plans and recovery techniques. An expeditious strategy for elimination or reduction of import reliance is recovery, and improved recovery efficiency, of Sb, As, Bi, Re, and Te, and possibly Ga, Ge, In, Ni, Sn, Ti, and W; during concentration and refining of copper and molybdenum minerals in ores of operating porphyry Cu-Mo mines; and in unmined porphyry Cu-Mo resources. These chalcophile, siderophile, and lithophile critical minerals, often undetectable in ore, are concentrated (hundreds of parts per million to percents) in slimes and electrolyte during copper electrorefining or could be recovered, in part, during sulfide concentration and smelting. Other than rhenium (recovered during molybdenum refining) and tellurium, all have been routinely discarded. Subsidization (for example, commodity price guarantees, tax credits, recovery technology development), political initiative, and (or) sustained market favorability could support new production of critical mineral commodities from subduction-related magmatic-hydrothermal deposits in Western States. In addition, insufficient domestic refining capacity could relegate the large inventories of critical minerals in porphyry Cu-Mo reserves and resources (for example, Pebble, Alaska; Resolution and Copper World [Rosemont], Arizona) to exportation in concentrates and importation insecurity, fortifying their present status.

Scientific Investigations Report↗
USGS1974

Effects of land use and retention practices on sediment yields in the Stony Brook basin, New Jersey

The average annual rate of suspended-sediment discharge of the Stony Brook at Princeton, N.J. (44.5 square miles) is about 8,800 tons, or 200 tons per square mile. Annual yields within the basin, which is in the Piedmont Lowlands section of the Piedmont physiographic province in west-central New Jersey, range from 25 to 400 tons per square mile. Storm runoff that transports suspended materials in excess of a ton carries 90 percent of the total suspended-sediment discharge from the basin. Observations of particlesize distributions indicate that the suspended material carried during storms is 55 percent silt, 40 percent clay, and 5 percent sand. A trend analysis of sediment records collected at Princeton between 1956 and 1970 indicated an increase in suspended-sediment discharge per unit of water discharge during 1956-61. From early 1962 to late 1967, sediment trends were difficult to interpret owing to complicating factors, such as reservoir construction, urbanization, and extreme drought. After 1967, yields decreased. Variations in sediment yields during the study are attributed to the integrated influence of several factors. A 2.9 percent decrease in croplands and an increase of 5.1 percent in idle and urban land use probably produced a net increase in sediment yields. Construction of seven sediment-retention reservoirs under Public Law 566 resulted in temporary increases in sediment yields. However, based on a trap-efficiency investigation at 1 site, the combined effect of operation of these 7 reservoirs is estimated to result in a 20 percent reduction in sediment discharge from the basin. Other factors that influence the noted decrease include reduction in yields during 5 years of drought, 1962-66, and reduced construction and development during the latter part of the study period resulting from a general economic slowdown.

Water Supply Paper↗
USGS2006

Surface-Water Quality and Nutrient Loads in the Nepaug Reservoir Watershed, Northwestern Connecticut, 1999-2001

Water quality was characterized at three tributary watersheds to the Nepaug Reservoir-Nepaug River, Phelps Brook, and Clear Brook-from October 1998 through September 2001 to document existing water-quality conditions and evaluate potential future effects of the removal of sand and gravel from areas of the watershed. Some removal operations may include removal of vegetation and top soil and steepening of slopes. Routine water samples collected monthly in all three watersheds were analyzed for nutrients, organic carbon, major ions, and fecal indicator bacteria. Results of the analyses indicate that, in general, the water quality in all three tributary watersheds is good and meets standards established for drinking-water supplies for nitrate, but does not always meet contact-recreation standards for bacteria. Median concentrations of total nitrogen, total phosphorus, and total organic carbon were highest in the routine monthly samples from Phelps Brook and lowest from Clear Brook. Samples also were collected during selected storms to examine changes in concentrations of nutrients during periods of high streamflow. The maximum values measured for total nitrogen, total phosphorus, and total organic carbon were in storm samples from Clear Brook. The Nepaug River watershed delivered the largest loads of total nitrogen, total phosphorus, and total organic carbon to the reservoir. Yields of nutrients and organic carbon differed significantly from year to year and among the three watersheds. Yields of total nitrogen and total organic carbon were largest from Phelps Brook and smallest from Clear Brook. The yields of total phosphorus were largest from Nepaug River and smallest from Phelps Brook. In comparison to other watersheds in Connecticut, annual loads and yields from the three streams were lower than those of developed urban areas and comparable to those of other rural and forested basins. Delivery of nutrients and organic carbon to the reservoir took place mostly during the spring with the exception of those constituents delivered during Tropical Storm Floyd, a large fall storm.

Scientific Investigations Report↗
USGS2003

Computation and analysis of the instantaneous-discharge record for the Colorado River at Lees Ferry, Arizona — May 8, 1921, through September 30, 2000

A gaging station has been operated by the U.S. Geological Survey at Lees Ferry, Arizona, since May 8, 1921. In March 1963, Glen Canyon Dam was closed 15.5 miles upstream, cutting off the upstream sediment supply and regulating the discharge of the Colorado River at Lees Ferry for the first time in history. To evaluate the pre-dam variability in the hydrology of the Colorado River, and to determine the effect of the operation of Glen Canyon Dam on the downstream hydrology of the river, a continuous record of the instantaneous discharge of the river at Lees Ferry was constructed and analyzed for the entire period of record between May 8, 1921, and September 30, 2000. This effort involved retrieval from the Federal Records Centers and then synthesis of all the raw historical data collected by the U.S. Geological Survey at Lees Ferry. As part of this process, the peak discharges of the two largest historical floods at Lees Ferry, the 1884 and 1921 floods, were reanalyzed and recomputed. This reanalysis indicates that the peak discharge of the 1884 flood was 210,000±30,000 cubic feet per second (ft 3 /s), and the peak discharge of the 1921 flood was 170,000±20,000 ft 3 /s. These values are indistinguishable from the peak discharges of these floods originally estimated or published by the U.S. Geological Survey, but are substantially less than the currently accepted peak discharges of these floods. The entire continuous record of instantaneous discharge of the Colorado River at Lees Ferry can now be requested from the U.S. Geological Survey Grand Canyon Monitoring and Research Center, Flagstaff, Arizona, and is also available electronically at http://www.gcmrc.gov. This record is perhaps the longest (almost 80 years) high-resolution (mostly 15- to 30-minute precision) times series of river discharge available. Analyses of these data, therefore, provide an unparalleled characterization of both the natural variability in the discharge of a river and the effects of dam operations on a river. Following the construction and quality-control checks of the continuous record of instantaneous discharge, analyses of flow duration, sub-daily flow variability, and flood frequency were conducted on the pre- and post-dam parts of the record. These analyses indicate that although the discharge of the Colorado River varied substantially prior to the closure of Glen Canyon Dam in 1963, operation of the dam has caused changes in discharge that are more extreme than the pre-dam natural variability. Operation of the dam has eliminated flood flows and base flows, and thereby has effectively "flattened" the annual hydrograph. Prior to closure of the dam, the discharge of the Colorado River at Lees Ferry was lower than 7,980 ft 3 /s half of the time. Discharges lower than about 9,000 ft 3 /s were important for the seasonal accumulation and storage of sand in the pre-dam river downstream from Lees Ferry. The current operating plan for Glen Canyon Dam no longer allows sustained discharges lower than 8,000 ft 3 /s to be released. Thus, closure of the dam has not only cut off the upstream supply of sediment, but operation of the dam has also largely eliminated discharges during which sand could be demonstrated to accumulate in the river. In addition to radically changing the hydrology of the river, operation of the dam for hydroelectric-power generation has introduced large daily fluctuations in discharge. During the pre-dam era, the median daily range in discharge was only 542 ft 3 /s, although daily ranges in discharge exceeding 20,000 ft 3 /s were observed during the summer thunderstorm season. Relative to the pre-dam period of record, dam operations have increased the daily range in discharge during all but 0.1 percent of all days. The post-dam median daily range in discharge, 8,580 ft 3 /s, exceeds the pre-dam median discharge of 7,980 ft 3 /s. Operation of the dam has also radically changed the frequency of floods on the Colorado River at Lees Ferry. The frequency of floods with peak discharges larger than about 29,000 ft 3 /s has greatly decreased, while the frequency of smaller floods, with peak discharges between 18,500 and 29,000 ft 3 /s, has increased substantially. Operation of the dam has greatly extended the duration of smaller floods; for example, each of the four longest periods of sustained flows in excess of 18,500 ft 3 /s occurred after closure of the dam.

Arizona↗