Geology topics

Research about Colorado River Basin

Source-linked reports with geographic coverage including Colorado River Basin.

35 records · Page 2Linked to original sources

USGS2016

Tamarisk beetle ( Diorhabda spp.) in the Colorado River basin: Synthesis of an expert panel forum

Executive Summary In 2001, the U.S. Department of Agriculture approved the release of a biological control agent, the tamarisk beetle ( Diorhabda spp.), to naturally control tamarisk populations and provide a less costly, and potentially more effective, means of removal compared with mechanical and chemical methods. The invasive plant tamarisk ( Tamarix spp.; saltcedar) occupies hundreds of thousands of acres of river floodplains and terraces across the western half of the North American continent. Its abundance varies, but can include dense monocultures, and can alter some physical and ecological processes associated with riparian ecosystems. The tamarisk beetle now occupies hundreds of miles of rivers throughout the Upper Colorado River Basin (UCRB) and is spreading into the Lower Basin. The efficacy of the beetle is evident, with many areas repeatedly experiencing tamarisk defoliation. While many welcome the beetle as a management tool, others are concerned by the ecosystem implications of widespread defoliation of a dominant woody species. As an example, defoliation may possibly affect the nesting success of the endangered southwestern willow flycatcher ( Empidonax traillii extimus ). In January 2015, the Tamarisk Coalition convened a panel of experts to discuss and present information on probable ecological trajectories in the face of widespread beetle presence and to consider opportunities for restoration and management of riparian systems in the Colorado River Basin (CRB). An in-depth description of the panel discussion follows.

Arizona, California, Chihuahua, Colorado, Idaho, K↗

USGS2015

Hydrologic implications of GRACE satellite data in the Colorado River Basin

Use of GRACE (Gravity Recovery and Climate Experiment) satellites for assessing global water resources is rapidly expanding. Here we advance application of GRACE satellites by reconstructing long-term total water storage (TWS) changes from ground-based monitoring and modeling data. We applied the approach to the Colorado River Basin which has experienced multiyear intense droughts at decadal intervals. Estimated TWS declined by 94 km 3 during 1986–1990 and by 102 km 3 during 1998–2004, similar to the TWS depletion recorded by GRACE (47 km 3 ) during 2010–2013. Our analysis indicates that TWS depletion is dominated by reductions in surface reservoir and soil moisture storage in the upper Colorado basin with additional reductions in groundwater storage in the lower basin. Groundwater storage changes are controlled mostly by natural responses to wet and dry cycles and irrigation pumping outside of Colorado River delivery zones based on ground-based water level and gravity data. Water storage changes are controlled primarily by variable water inputs in response to wet and dry cycles rather than increasing water use. Surface reservoir storage buffers supply variability with current reservoir storage representing ∼2.5 years of available water use. This study can be used as a template showing how to extend short-term GRACE TWS records and using all available data on storage components of TWS to interpret GRACE data, especially within the context of droughts.

Water Resources Research↗

USGS2015

U.S. Geological Survey National Water Census: Colorado River Basin Geographic Focus Area Study

Introduction The U.S. Geological Survey’s (USGS) concept of a national census (or accounting) of water resources has evolved over the last several decades as the Nation has experienced increasing concern over water availability for multiple competing uses. The implementation of a USGS National Water Census was described in the USGS 2007 science strategy document that identified the highest priority science topics for the decade 2007–17. In 2009, the SECURE Water Act (Public Law 111–11, subtitle F) authorized the USGS to create a Water Availability and Use Assessment Program for the Nation, and in 2012, the Department of the Interior WaterSMART initiative provided funding to begin implementation of the USGS National Water Census (NWC). Generally, the USGS NWC approaches water-availability assessment in terms of a “water budget.” The water-budget approach seeks to better quantify the inflows and outflows of water, as well as the change in storage volume, both nationally and at a regional scale and, by doing so, provides critical information to managers and stakeholders responsible for making water-availability decisions. The NWC has two primary components: Topical Studies and Geographic Focus Area Studies. Topical Studies do research on methods that can provide nationwide estimates of particular water-budget components at the subwatershed scale. Some examples of NWC Topical Studies include estimation of streamflow at ungaged locations; periodic quantification of evapotranspiration; and water use related to development of unconventional oil and gas. These efforts are planned to include additional topics in the future. Geographic Focus Area Studies (FASs) assess water availability and use within a defined geographic area, typically a surface-water drainage basin, to increase the understanding of factors affecting water availability in the region. In the FASs, local stakeholder input helps the USGS identify what components of the water budget are in most need of additional understanding or quantification. Focus Area Studies are planned as 3-year efforts and, typically, three FASs are ongoing in different parts of the country at any given time. The Colorado River Basin (CRB) and the Delaware and Apalachicola-Chattahoochee-Flint (ACF) River Basins were selected by the Department of the Interior for the first round of FASs because of the perceived water shortages in the basins and potential conflicts over water supply and allocations. After gathering input from numerous stakeholders in the CRB, the USGS determined that surface-water resources in the basin were already being closely monitored and that the most important scientific contribution could be made by helping to improve estimates of four water-budget components: evapotranspiration losses, snowpack hydrodynamics, water-use information, and the relative importance of groundwater discharge in supporting streamflow across the basin. The purpose of this fact sheet is to provide a brief summary of the CRB FAS results as the study nears completion. Although some project results are still in the later stages of review and publication, this fact sheet provides an overall description of the work completed and cites the publications in which additional information can be found.

Arizona, California, Colorado, Nevada, New Mexico,↗

USGS2014

Updated estimates of long-term average dissolved-solids loading in streams and rivers of the Upper Colorado River Basin

The Colorado River and its tributaries supply water to more than 35 million people in the United States and 3 million people in Mexico, irrigating over 4.5 million acres of farmland, and annually generating about 12 billion kilowatt hours of hydroelectric power. The Upper Colorado River Basin, part of the Colorado River Basin, encompasses more than 110,000 mi 2 and is the source of much of more than 9 million tons of dissolved solids that annually flows past the Hoover Dam. High dissolved-solids concentrations in the river are the cause of substantial economic damages to users, primarily in reduced agricultural crop yields and corrosion, with damages estimated to be greater than 300 million dollars annually. In 1974, the Colorado River Basin Salinity Control Act created the Colorado River Basin Salinity Control Program to investigate and implement a broad range of salinity control measures. A 2009 study by the U.S. Geological Survey, supported by the Salinity Control Program, used the Spatially Referenced Regressions on Watershed Attributes surface-water quality model to examine dissolved-solids supply and transport within the Upper Colorado River Basin. Dissolved-solids loads developed for 218 monitoring sites were used to calibrate the 2009 Upper Colorado River Basin Spatially Referenced Regressions on Watershed Attributes dissolved-solids model. This study updates and develops new dissolved-solids loading estimates for 323 Upper Colorado River Basin monitoring sites using streamflow and dissolved-solids concentration data through 2012, to support a planned Spatially Referenced Regressions on Watershed Attributes modeling effort that will investigate the contributions to dissolved-solids loads from irrigation and rangeland practices.

Arizona, Colorado, New Mexico, Utah, Wyoming↗

USGS2014

Assessment of dissolved-solids loading to the Colorado River in the Paradox Basin between the Dolores River and Gypsum Canyon, Utah

Salinity loads throughout the Colorado River Basin have been a concern over recent decades due to adverse impacts on population, natural resources, and regional economics. With substantial financial resources and various reclamation projects, the salt loading to Lake Powell and associated total dissolved-solids concentrations in the Lower Colorado River Basin have been substantially reduced. The Colorado River between its confluence with the Dolores River and Lake Powell traverses a physiographic area where saline sedimentary formations and evaporite deposits are prevalent. However, the dissolved-solids loading in this area is poorly understood due to the paucity of water-quality data. From 2003 to 2011, the U.S. Geological Survey in cooperation with the U.S. Bureau of Reclamation conducted four synoptic sampling events to quantify the salinity loading throughout the study reach and evaluate the occurrence and impacts of both natural and anthropogenic sources. The results from this study indicate that under late-summer base-flow conditions, dissolved-solids loading in the reach is negligible with the exception of the Green River, and that variations in calculated loads between synoptic sampling events are within measurement and analytical uncertainties. The Green River contributed approximately 22 percent of the Colorado River dissolved-solids load, based on samples collected at the lower end of the study reach. These conclusions are supported by water-quality analyses for chloride and bromide, and the results of analyses for the stable isotopes of oxygen and deuterium. Overall, no significant sources of dissolved-solids loading from tributaries or directly by groundwater discharge, with the exception of the Green River, were identified in the study area.

Utah↗

USGS2013

Actual evapotranspiration (water use) assessment of the Colorado River Basin at the Landsat resolution using the operational simplified surface energy balance model

Accurately estimating consumptive water use in the Colorado River Basin (CRB) is important for assessing and managing limited water resources in the basin. Increasing water demand from various sectors may threaten long-term sustainability of the water supply in the arid southwestern United States. We have developed a first-ever basin-wide actual evapotranspiration (ET a ) map of the CRB at the Landsat scale for water use assessment at the field level. We used the operational Simplified Surface Energy Balance (SSEBop) model for estimating ET a using 328 cloud-free Landsat images acquired during 2010. Our results show that cropland had the highest ET a among all land cover classes except for water. Validation using eddy covariance measured ET a showed that the SSEBop model nicely captured the variability in annual ET a with an overall R 2 of 0.78 and a mean bias error of about 10%. Comparison with water balance-based ETa showed good agreement (R 2 = 0.85) at the sub-basin level. Though there was good correlation (R 2 = 0.79) between Moderate Resolution Imaging Spectroradiometer (MODIS)-based ETa (1 km spatial resolution) and Landsat-based ET a (30 m spatial resolution), the spatial distribution of MODIS-based ET a was not suitable for water use assessment at the field level. In contrast, Landsat-based ET a has good potential to be used at the field level for water management. With further validation using multiple years and sites, our methodology can be applied for regular production of ET a maps of larger areas such as the conterminous United States.

Arizona, California, Colorado, Nevada, New Mexico,↗

USGS2013

Combined impacts of current and future dust deposition and regional warming on Colorado River Basin snow dynamics and hydrology

The Colorado River provides water to 40 million people in seven western states and two countries and to 5.5 million irrigated acres. The river has long been overallocated. Climate models project runoff losses of 5–20% from the basin by mid-21st century due to human-induced climate change. Recent work has shown that decreased snow albedo from anthropogenic dust loading to the CO mountains shortens the duration of snow cover by several weeks relative to conditions prior to western expansion of the US in the mid-1800s, and advances peak runoff at Lees Ferry, Arizona, by an average of 3 weeks. Increases in evapotranspiration from earlier exposure of soils and germination of plants have been estimated to decrease annual runoff by more than 1.0 billion cubic meters, or ~5% of the annual average. This prior work was based on observed dust loadings during 2005–2008; however, 2009 and 2010 saw unprecedented levels of dust loading on snowpacks in the Upper Colorado River Basin (UCRB), being on the order of 5 times the 2005–2008 loading. Building on our prior work, we developed a new snow albedo decay parameterization based on observations in 2009/10 to mimic the radiative forcing of extreme dust deposition. We convolve low, moderate, and extreme dust/snow albedos with both historic climate forcing and two future climate scenarios via a delta method perturbation of historic records. Compared to moderate dust, extreme dust absorbs 2× to 4× the solar radiation, and shifts peak snowmelt an additional 3 weeks earlier to a total of 6 weeks earlier than pre-disturbance. The extreme dust scenario reduces annual flow volume an additional 1% (6% compared to pre-disturbance), a smaller difference than from low to moderate dust scenarios due to melt season shifting into a season of lower evaporative demand. The sensitivity of flow timing to dust radiative forcing of snow albedo is maintained under future climate scenarios, but the sensitivity of flow volume reductions decreases with increased climate forcing. These results have implications for water management and suggest that dust abatement efforts could be an important component of any climate adaptation strategies in the UCRB.

Arizona, Colorado, New Mexico, Utah, Wyoming↗

USGS2012

WaterSMART-The Colorado River Basin focus-area study

Increasing demand for the limited water resources of the United States continues to put pressure on water-resource agencies to balance the competing needs of ecosystem health with municipal, agricultural, and recreational uses. In 2007, the U.S. Geological Survey (USGS) identified a National Water Census as one of six pivotal future science directions for the USGS in the following decade. The envisioned USGS National Water Census would evaluate large-scale effects of changes in land use and land cover, water use, and climate on water availability, water quality, and human and aquatic ecosystem health. The passage of the SECURE (Science and Engineering to Comprehensively Understand and Responsibly Enhance) Water Act in 2009 was a key step towards implementing the USGS National Water Census. Section 9508 of the Act authorizes a "national water availability and use assessment program" within the USGS (1) to provide a more accurate assessment of the status of the water resources of the United States; and (2) to develop the science for improved forecasts of the availability of water for future economic, energy production, and environmental uses. Initial funding for the USGS to begin working on the National Water Census came with the approval of the U.S. Department of the Interior's WaterSMART (Sustain and Manage America's Resources for Tomorrow) Initiative. The WaterSMART Initiative provides funding to the USGS, Bureau of Reclamation, and U.S. Department of Energy to achieve a sustainable water strategy to meet the Nation's water needs. WaterSMART funding also allowed the USGS to begin the national Water Availability and Use Assessment, as called for under the SECURE Water Act.

Arizona;Colorado;New Mexico;Utah↗

USGS2007

Chemical contaminants, health indicators, and reproductive biomarker responses in fish from the Colorado River and its tributaries

Common carp (Cyprinus carpio), black bass (Micropterus spp.), and channel catfish (Ictalurus punctatus) were collected from 14 sites in the Colorado River Basin (CRB) to document spatial trends in accumulative contaminants, health indicators, and reproductive biomarkers. Organochlorine residues, 2,3,7,8-tetrachlorodibenzo-p-dioxin-like activity (TCDD-EQ), and elemental contaminants were measured in composite samples of whole fish, grouped by species and gender, from each site. Selenium (Se) and mercury (Hg) concentrations in fish were elevated throughout the CRB, and pesticide concentrations were greatest in fish from agricultural areas in the Lower Colorado River and Gila River. Selenium concentrations exceeded toxicity thresholds for fish (> 1.0????g/g ww) at all CRB sites except the Gila River at Hayden, Arizona. Mercury concentrations were elevated (> 0.1????g/g ww) in fish from the Yampa River at Lay, Colorado; the Green River at Ouray National Wildlife Refuge (NWR), Utah and San Rafael, Utah; the San Juan River at Hogback Diversion, New Mexico; and the Colorado River at Gold Bar Canyon, Utah, Needles, California, and Imperial Dam, Arizona. Concentrations of p,p???-DDE were relatively high in fish from the Gila River at Arlington, Arizona (> 1.0????g/g ww) and Phoenix, Arizona (> 0.5????g/g ww). Concentrations of other formerly used pesticides including toxaphene, total chlordanes, and dieldrin were also greatest at these two sites but did not exceed toxicity thresholds. Currently used pesticides such as Dacthal, endosulfan, ??-HCH, and methoxychlor were also greatest in fish from the Gila River downstream of Phoenix. Total polychlorinated biphenyls (PCBs; > 0.11????g/g ww) and TCDD-EQs (> 5??pg/g ww) exceeded wildlife guidelines in fish from the Gila River at Phoenix. Hepatic ethoxyresorufin O-deethylase (EROD) activity was also relatively high in carp from the Gila River at Phoenix and in bass from the Green River at Ouray NWR. Fish from some sites showed evidence of contaminant exposure as indicated by fish health indicators and reproductive biomarker results. Multiple health indicators including altered body and organ weights and high health assessment index scores may be associated with elevated Se concentrations in fish from the Colorado River at Loma, Colorado and Needles. Although grossly visible external or internal lesions were found on most fish from some sites, histopathological analysis determined many of these to be inflammatory responses associated with parasites. Edema, exophthalmos, and cataracts were noted in fish from sites with elevated Se concentrations. Intersex fish were found at seven of 14 sites and included smallmouth bass (M. dolomieu), largemouth bass (M. salmoides), catfish, and carp and may indicate exposure to endocrine disrupting compounds. A high proportion of smallmouth bass from the Yampa River at Lay (70%) was intersex but the cause of this condition is unknown. Male carp, bass, and catfish with low concentrations of vitellogenin were common in the CRB. Comparatively high vitellogenin concentrations (> 0.2??mg/mL) were measured in male bass from the Green River at Ouray NWR and the Colorado River at Imperial Dam and indicate exposure to estrogenic or anti-androgenic chemicals. Anomalous reproductive biomarkers including low GSI and gonadal abnormalities (calcifications, edema, and parasites) observed in fish downstream of Phoenix are likely related to the poor water-quality of the Gila River in this area.

Colorado River Basin↗

USGS2003

Hydrologic properties and ground-water flow systems of the Paleozoic rocks in the upper Colorado River basin in Arizona, Colorado, New Mexico, Utah, and Wyoming, excluding the San Juan Basin

The hydrologic properties and ground-water flow systems of Paleozoic sedimentary rocks in the Upper Colorado River Basin were investigated under the Regional Aquifer-System Analysis (RASA) program of the U.S. Geological Survey in anticipation of the development of water supplies from bedrock aquifers to fulfill the region's growing water demands. The study area, in parts of Arizona, Colorado, New Mexico, Utah, and Wyoming, covers about 100,000 square miles. It includes parts of four physiographic provinces--the Middle Rocky Mountains, Wyoming Basin, Southern Rocky Mountains, and Colorado Plateaus. A variety of landforms, including mountains, plateaus, mesas, cuestas, plains, badlands, and canyons, are present. Altitudes range from 3,100 to 14,500 feet. Precipitation is distributed orographically and ranges from less than 6 inches per year at lower altitudes to more than 60 inches per year in some mountainous areas. Most of the infrequent precipitation at altitudes of less than 6,000 feet is consumed by evapotranspiration. The Colorado and Green Rivers are the principal streams: the 1964-82 average discharge of the Colorado River where it leaves the Upper Colorado River Basin is 12,170 cubic feet per second (a decrease of 5,680 cubic feet per second since construction of Glen Canyon Dam in 1963). On the basis of their predominant lithologic and hydrologic properties, the Paleozoic rocks are classified into four aquifers and three confining units. The Flathead aquifer, Gros Ventre confining unit, Bighorn aquifer, Elbert-Parting confining unit, and Madison aquifer (Redwall-Leadville and Darwin-Humbug zones) make up the Four Corners aquifer system. A thick sequence, composed mostly of Mississippian and Pennsylvanian shale, anhydrite, halite, and carbonate rocks--the Four Corners confining unit (Belden-Molas and Paradox-Eagle Valley subunits)--overlies the Four Corners aquifer system in most areas and inhibits vertical ground-water flow between the Four Corners aquifer system and the overlying Canyonlands aquifer. Composed of the uppermost Paleozoic rocks, the Canyonlands aquifer consists, in ascending order, of the Cutler-Maroon, Weber-De Chelly, and Park City-State Bridge zones. The Paleozoic rocks are underlain by a basal confining unit consisting of Precambrian sedimentary, igneous, and metamorphic rocks and overlain throughout most of the Upper Colorado River Basin by the Chinle-Moenkopi confining unit, which consists of Triassic formations composed mostly of shale. The largest values of porosity, permeability, hydraulic conductivity, transmissivity, and artesian yield are exhibited by the Redwall-Leadville zone of the Madison aquifer and the Weber-De Chelly zone of the Canyonlands aquifer. The former consists almost entirely of Devonian and Mississippian carbonate rocks: the latter consists mostly of Pennsylvanian and Permian quartz sandstone. Unit-averaged porosity in hydrogeologic units composed of Paleozoic rocks ranges from less than 1 to 28 percent. Permeability ranges from less than 0.0001 to 3,460 millidarcies. Unit-averaged hydraulic conductivity ranges from 0.000005 to 200 feet per day. The composite transmissivity of Paleozoic rocks ranges from 0.0005 to 47,000 feet squared per day. Artesian yields to wells and springs (excluding atypical springflows) from these hydrogeologic units range from less than 1 to 10,000 gallons per minute. The permeability and watersupply capabilities of all hydrogeologic units progressively decrease from uplifted areas to structural basins. Recharge to the Paleozoic rocks is provided by direct infiltration of precipitation, leakage from streams, and ground-water inflows from structurally continuous areas west and north of the Upper Colorado River Basin. The total recharge available from ground-water systems in the basin from direct precipitation and stream leakage is estimated to be 6,600,000 acre-feet per year. However, little of this recharge directly enters the Paleozoic rocks

Arizona, Colorado, New Mexico, Utah, Wyoming↗

USGS1986

Statistical summary and evaluation of the quality of surface water in the Colorado River basin, 1973-82 water years

Significant upward trends in dissolved-solids concentrations were detected with the Seasonal Kendall Test for trends at three stations in the upper basin during the study period. The increases exceeded 270 milligrams per liter per year at two stations and 165 milligrams per liter per year at the third station. The composition of dissolved constituents in the Colorado River basin changes from predominantly sodium and chloride ions in the upper basin to predominantly calcium and bicarbonate ions in the lower basin. The U.S. Environmental Protection Agency secondary drinking-water regulations of 500 milligrams per liter for total dissolved solids was exceeded 95 percent of the time at each station on the main stem of the Colorado River in the upper basin. In the middle Colorado River basin, the Environmental Protection Agency secondary drinking-water regulations for total dissolved solids was exceeded approximately 95 percent of the time at most stations. Nutrient concentrations in the Colorado River basin generally were low. Only one sample exceeded the level set for nitrate nitrogen, and no other nutrient species exceeded Environmental Protection Agency levels. A general upward trend was detected in organic nitrogen and total nitrogen, but concentrations still remained low. Densities of fecal-col iform and fecal-streptococcal bacteria ranged from less than 1 colony per 100 milliliters to 26,000 colonies per 100 milliliters and 1 colony per 100 milliliters to 50,000 colonies per 100 milliliters, respectively. Fecal-coliform densities exceeded Environmental Protection Agency criteria for public water supply (2,000 colonies per 100 milliliters) at several stations during the study. Biochemical oxygen demand concentrations ranged from 0.00 to 34 milligrams per liter. Only one mean biochemical oxygen demand concentration exceeded 8 milligrams per liter, the upper range of concentration common in moderately contaminated streams. Trace elements and pesticides were detected in many samples throughout the basin. The concentrations generally were low, and maximum contaminant levels rarely were exceeded.

Texas↗

USGS1976

Estimating runoff volumes and flood hydrographs in the Colorado River Basin, southern Utah

Hydrographs of 364 floods from 18 continuous-record gaging sites in the Colorado River basin in southern Utah were used to define a single relation of flood volume to peak discharge; the standard error of estimate of that relation . is 82 percent. Using the same data, a mean dimensionless hydrograph was pre-pared. Synthetic hydrographs may be derived for basins of 5 to 300 square miles (13 to 780 square kilometers) and flood peaks of 1 to 7,000 cubic feet per second (0.03 to 200 cubic meters per second) using that mean dimensionless hydrograph. Design flood peaks may be estimated from other reports. A method is presented to estimate the reduction in culvert or bridge size resulting from use of storage above the structure. Reduction of structure capacity of 25 percent may be achieved by storing 4 percent of the total flood volume.

Utah↗

USGS1973

Selected hydrologic data in the upper Colorado River basin

Most of the information in this atlas pertains to the ground-water resources of the basin. The surface-water resources, climate, and geohydrologic framework have been described in considerable detail by Iorns and others (1964, 1965). The maps in this atlas are highly generalized, and are intended to provide the reader with only a general understanding of the geology, ground-water conditions, and chemical quality of the water in the basin as a whole. In most instances, the availability, depth to, and chemical quality of ground water at a given well site can be determined only by special investigations. Only previously collected data were used to compile the maps in this atlas. More detailed information for specific parts of the basin can be found in the reports and maps in the list of references.

Arizona, Colorado, New Mexico, Utah, Wyoming↗

USGS1970

Correlative estimates of streamflow in the upper Colorado River basin

Most hydrologic analyses, whether for appraisal of the water resource, feasibility of a particular development, design of a system of operation, assessment of gains or losses from acts of man or natural changes, or almost any other use, require the extension in time of some streamflow records. In the Upper Colorado River Basin, streamflow records have been extended by various agencies from time to time to fulfill their individual needs, resulting in different estimates of flow for the same point and time. The purpose of this report is to provide correlative estimates of monthly mean discharge at discontinued streamflow gaging stations so that all users will have access to a single set of data. Estimates of monthly mean discharge for periods other than the period of actual record are given for certain discontinued streamflow gaging stations. The stations selected were discontinued in recent years, but they have a sufficient length of record to permit development of a meaningful correlation with the records for a nearby long-term gaging station. Where possible, estimates of monthly mean discharge are made to provide a complete record, estimated or measured, from 1930 to 1965. However, where the long-term gaging station record encompasses a shorter period, the estimates cover only that shorter period. Estimates for periods prior to 1930 were not made, although these may be computed for a few stations. Lack of a related long-term gaging-station record prevented the extension of records at many discontinued stations. The area covered in this report (fig. 1) is that defined in the Colorado River Compact of 1922, as the Upper Basin "those parts of the States of Arizona, Colorado, New Mexico, Utah, and Wyoming within and from which waters naturally drain into the Colorado River System above Lee Ferry," 1 but excluding "all parts of said States located without the drainage area of the Colorado River System which are now and shall hereafter be beneficially served by waters diverted from the System above Lee Ferry" (Wilbur and Ely, 1948, p. A18).

Colorado River Basin↗

USGS1963

Effects of drought in the Colorado River basin: Chapter F in Drought in the Southwest, 1942-56

The prolonged drought of 1942-56 affected chiefly the lower part of the Colorado River basin and did not extend into the upper basin (the chief water-producing area) until 1953. Areas served by the Colorado River had adequate water supplies in spite of the local deficiency of precipitation. In the Gila River basin, there was a deficiency of streamflow during the drought years, and the water requirements of the present population exceed the yield of the basin even during years of average precipitation; the deficiency is overcome by mining of ground water.

Arizona, California, Colorado, Nevada, New Mexico,↗

USGS1947

Summary of records of surface waters at stations on tributaries in lower Colorado River Basin, 1888-1938

This report presents summaries of records of discharge at gaging stations on tributaries in the Lower Colorado River Basin. The lower Colorado River Basin as used in this report is the "lower basin" defined in the Colorado River Compact, as that part of the Colorado River Basin below a point 1 mile downstream from the mouth of Paria River. Records for Paria River, also included in this report, when combined with those for Colorado River at Lees Ferry show the flow at the point of division between the upper and lower basins. This report and water-Supply Paper 918, "Summary of Records of Surface waters at Base Stations in Colorado River Basin, 1891-1938", furnish a complete compilation of all records of surface waters collected by the Geological Survey in the Lower Colorado River Basin prior to October 1, 1938, and contain all stream-flow records collected in Arizona prior to that date. Records for 16 gaging stations, which are base stations on tributaries and canals, are given in both reports.

Colorado River Basin↗

USGS1946

Notable local floods of 1939: Part 1: Floods of September 1939 in Colorado River Basin below Boulder Dam

Although the flow of Colorado River has been controlled at Boulder Dam since February 1935, flood danger still exists in the basin below the dam. This report on the first general floods to occur below Boulder lam since the dam was closed presents facts that should prove helpful in planning protection and reservoir operation to minimize the ill effects of future floods. The floods of September 1939 were caused by a series of tropical disturbances that moved northwestward along the west coast of Mexico and culminated in unprecedently heavy rains in northwestern Mexico and southwestern United States. Three separate storms, occurring September 3-7, 8-13, and 23-26, moved across the lower Colorado River Basin. At many points in that area the mean annual precipitation was exceeded by the precipitation for September. Because little rainfall preceded the storms, runoff from them was less than would have occurred under more unfavorable conditions. At streamflow measuring stations where past records are available no new records were set. On Gila River no flood occurred. On Colorado River the flood was not so great as those that had occurred almost every year prior to the closing of Boulder Dam. On Williams River, however, the peak discharge was of the magnitude of a major flood, and in many of the smaller drainage basins peaks occurred which probably have not been exceeded in the previous 50 to 100 years. The relatively low flood peaks on Colorado River do not mean that there was no flood danger. The regulation of the river since Boulder Dam was closed has prevented the scouring of the channel by floods, has permitted the encroachment of vegetation in the channel, and has allowed the accumulation of sediment. As a result, flood stages today are about as high as they formerly were for discharges twice as large. Flood peaks in Colorado River were greatly reduced by storage. Between September 5 and 20»Lake Mead stored 330,000 acre-feet of water. Between September 4 and 7 Havasu Lake stored 135,000 acre-feet, and the channel storage between Topock and Yuma, exclusive of Havasu Lake, accounted for about 110,000 acre-feet at the peak. Storage in Havasu Lake is limited in relation to the flood flows that may enter it. When the September storms began, Havasu Lake was at normal minimum level. Had it not been low, the lake probably would have filled by the morning of September 6, and that day's peak inflow, which may have exceeded 75,000 second-feet, would necessarily have passed through with little reduction.

Arizona, California, Nevada, Utah↗