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D. S. Morgan

Publications and source records attributed to D. S. Morgan.

6 recordsLinked to original sources
USGS2015

Groundwater availability of the Columbia Plateau Regional Aquifer System, Washington, Oregon, and Idaho

The Columbia Plateau Regional Aquifer System (CPRAS) covers about 44,000 square miles of southeastern Washington, northeastern Oregon, and western Idaho. The area supports a $6-billion per year agricultural industry, leading the Nation in production of apples, hops, and eight other commodities. Groundwater pumpage and surface-water diversions supply water to croplands that account for about 5 percent of the Nation’s irrigated lands. Groundwater also is the primary source of drinking water for the more than 1.3 million people in the study area. Increasing competitive demands for water for municipal, fisheries/ecosystems, agricultural, domestic, hydropower, and recreational uses must be met by additional groundwater withdrawals and (or) by changes in the way water resources are allocated and used throughout the hydrologic system. As of 2014, most surface-water resources in the study area were either over allocated or fully appropriated, especially during the dry summer season. In response to continued competition for water, numerous water-management activities and concerns have gained prominence: water conservation, conjunctive use, artificial recharge, hydrologic implications of land-use change, pumpage effects on streamflow, and effects of climate variability and change. An integrated understanding of the hydrologic system is important in order to implement effective water-resource management strategies that address these concerns. To provide information to stakeholders involved in water-management activities, the U.S. Geological Survey (USGS) Groundwater Resources Program assessed the groundwater availability as part of a national study of regional systems (U.S. Geological Survey, 2008). The CPRAS assessment includes: The present status of groundwater resources, How these resources have changed over time, and Development and application of tools to estimate system responses to stresses from future uses and climate variability and change. This effort builds on previous investigations, especially the USGS Columbia Plateau Regional Aquifer-System Analysis study (CP-RASA). A major product of this new assessment is a numerical groundwater-flow model of the system. The model was used to estimate water-budget components of the hydrogeologic units composing the groundwater system, and to evaluate groundwater availability under existing land- and water-use conditions and a possible future climate scenario representing an increase in pumpage demand due to a warming climate. Information from this study also allowed for analysis of: The CPRAS for predevelopment times (pre-1920), Variations from 1920 through 2007, Conditions during 1985–2007 (referred to as “existing conditions”), and Changes in the system from predevelopment times. The model also is a useful tool for investigating water supply, water demand, management strategies, groundwater-surface water exchanges, and potential effects of changing climate on the hydrologic system.

Idaho, Oregon, Washington↗
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↗
USGS1996

Numerical model analysis of the effects of ground-water withdrawals on discharge to streams and springs in small basins typical of the Puget Sound Lowland, Washington

A numerical ground-water flow model of a hypothetical basin was constructed and used to investigate the effects of ground-water withdrawals on rates of natural discharge to streams and springs in small basins of the Puget Sound Lowland. Definitions of the topography, geology, drainage, and climate of the hypothetical basin were based on the features of typical small basins in the Puget Sound Lowland. This information was used to construct a 13-layer numerical ground-water flow model capable of simulating water levels, hydraulic gradients, and discharge to streams and springs. Three sequences of glacial drift and interglacial deposits were simulated in the model; each sequence consisted of recessional outwash, till, advance, outwash, and fine-grained interglacial sediments. Alluvial sediments of the major stream valleys and undifferentiated glacial and interglacial deposits were also included in the model. The model was calibrated by comparing simulated hydrologic conditions with expected conditions and making adjustments to values of hydraulic characteristics as needed. The model was calibrated to predevelop- ment conditions (those prior to pumping), and then used to simulate the effects of pumping on natural discharge to streams and springs. Seven series of simulations were made to investigate the effects of (1) distance from the well to a stream, (2) the presence of confining layers, (3) pumping rate, (4) depth of the pumped aquifer, (5) distance from the well to a bluff, (6) well density, and (7) recharge rate. The discharge of wells pumping from unconfined outwash aquifers on the drift plains is derived almost entirely from capture of natural discharge to nearby stream reaches. Increasing the lateral distance between the well and stream caused more of the well discharge to be captured from other streams on the drift plain. Pumping from aquifers separated from the stream by one or more confining layers caused a reduction in the effects of pumping on discharge to nearby streams that was offset by an increase in the effects on discharge to more distant streams and springs. The percentage of well discharge captured from springs on the bluff was sensitive to the distance of wells from the bluff. Simulations also showed that increased well density caused greater water-level decline locally, but, at equilibrium, did not affect the extent of the area affected by reduction of natural discharge to streams and springs. Finally, decreased recharge in areas where development had created impervious surfaces had a direct effect on the natural discharge rates to streams and springs. Increased recharge, however, increased natural discharge and offset the effects of well withdrawals. Further analysis of the time-dependent effects of with- drawals would provide additional insights, but would require the development of a transient version of the model.

Open-File Report↗
USGS1994

Estimation of ground-water recharge from precipitation, runoff into drywells, and on-site waste-disposal systems in the Portland Basin, Oregon and Washington

The average recharge rate in the Portland Basin, in northwestern Oregon and southwestern Washington, is estimated to be about 22.0 inches per year. Of that amount, precipitation accounts for about 20.8 inches per year, runoff into drywells 0.9 inches per year, and on-site waste disposal about 0.4 inches per year. Recharge is highest, about 49 inches per year, in the Cascade Range. Recharge is lowest, near zero, along and between the Columbia and Willamette Rivers. Recharge is higher locally in discrete areas owing to recharge from runoff into drywells and on-site, waste-disposal systems in urbanized parts of the study area. In these urbanized areas, recharge ranges from 0 to 49 inches per year.

Water-Resources Investigations Report↗