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USGS2009

Streamflow-Characteristic Estimation Methods for Unregulated Streams of Tennessee

Streamflow-characteristic estimation methods for unregulated rivers and streams of Tennessee were developed by the U.S. Geological Survey in cooperation with the Tennessee Department of Environment and Conservation. Streamflow estimates are provided for 1,224 stream sites. Streamflow characteristics include the 7-consecutive-day, 10-year recurrence-interval low flow, the 30-consecutive-day, 5-year recurrence-interval low flow, the mean annual and mean summer flows, and the 99.5-, 99-, 98-, 95-, 90-, 80-, 70-, 60-, 50-, 40-, 30-, 20-, and 10-percent flow durations. Estimation methods include regional regression (RRE) equations and the region-of-influence (ROI) method. Both methods use zero-flow probability screening to estimate zero-flow quantiles. A low flow and flow duration (LFFD) computer program (TDECv301) performs zero-flow screening and calculation of nonzero-streamflow characteristics using the RRE equations and ROI method and provides quality measures including the 90-percent prediction interval and equivalent years of record. The U.S. Geological Survey StreamStats geographic information system automates the calculation of basin characteristics and streamflow characteristics. In addition, basin characteristics can be manually input to the stand-alone version of the computer program (TDECv301) to calculate streamflow characteristics in Tennessee. The RRE equations were computed using multivariable regression analysis. The two regions used for this study, the western part of the State (West) and the central and eastern part of the State (Central+East), are separated by the Tennessee River as it flows south to north from Hardin County to Stewart County. The West region uses data from 124 of the 1,224 streamflow sites, and the Central+East region uses data from 893 of the 1,224 streamflow sites. The study area also includes parts of the adjacent States of Georgia, North Carolina, Virginia, Alabama, Kentucky, and Mississippi. Total drainage area, a geology factor, a climate factor, and two soil factors were used as explanatory variables in the RRE equations. Average deleted-residual prediction errors for the West-region RRE equations were 18 and 123 percent for the 10-percent flow duration and 7-consecutive-day, 10-year recurrence-interval low flow, respectively. Average deleted-residual prediction errors for RRE equations were 21 and 89 percent for the same respective flow quantiles in the Central+East region. The ROI method calculates unique multivariable regression equations for a site of interest using the flow and basin characteristics of 45 similar streamflow-data sites selected from the same region. These 45 sites are selected using a metric that measures similarity between the site of interest and the streamflow-data sites based on total drainage area, geology factor, and climate factor. The ROI method estimates streamflow characteristics using total drainage area, geology factor, and a soil factor as explanatory variables. Average deleted-residual prediction errors for the West-region ROI equations were 18 and 125 percent for the 10-percent duration and 7-consecutive-day, 10-year recurrence-interval low flow, respectively. Average deleted-residual prediction errors for ROI equations were 20 and 85 percent for the same respective flow quantiles in the Central+East region. In general, when compared to the RRE equations, the ROI method performs similarly in the West region and reduces streamflow-characteristic prediction errors by an average of about 7 percent in the Central+East region of Tennessee.

Scientific Investigations Report↗

USGS1998

Comparison of rangeland vegetation sampling techniques in the Central Grasslands

Maintaining native plant diversity, detecting exotic species, and monitoring rare species are becoming important objectives in rangeland conservation. Four rangeland vegetation sampling techniques were compared to see how well they captured local pant diversity. The methods tested included the commonly used Parker transects, Daubenmire transects as modified by the USDA Forest Service, a new transect and 'large quadrat' design proposed by the USDA Agricultural Research Service, and the Modified-Whittaker multi-scale vegetation plot. The 4 methods were superimposed in shortgrass steppe, mixed grass prairie, northern mixed prairie, and tallgrass prairie in the Central Grasslands of the United States with 4 replicates in each prairie type. Analysis of variance tests showed significant method effects and prairie type effects, but no significant method X type interactions for total species richness, the number of native species, the number of species with less than 1 % cover, and the time required for sampling. The methods behaved similarly in each prairie type under a wide variety of grazing regimens. The Parker, large quadrat, and Daubenmire transects significantly underestimated the total species richness and the number of native species in each prairie type, and the number of species with less than 1 % cover in all but the tallgrass prairie type. The transect techniques also consistently missed half the exotic species, including noxious weeds, in each prairie type. The Modified-Whittaker method, which included an exhaustive search for plant species in a 20 x 50 m plot, served as the baseline for species richeness comparisons. For all prairie types, the Modified-Whittaker plot captured an average of 42. ( ± 2.4; 1 S.E.) plant species per site compared to 15.9 ( ± 1.3), 18.9 ( ± 1.2), and 22.8 ( ± 1.6) plant species per site using the Parker, large quadrat, and Daubenmire transect methods, respectively. The 4 methods captured most of the dominant species at each site and thus produced similar results for total foliar cover and soil cover. The detection and measurement of exotic plant species were greatly enhanced by using ten 1 m 2 subplots in a multi-scale sampling design and searching a larger area (1,000 m 2 ) at each site. Even with 4 replicate sites, the transect methods usually captured, and thus would monitor, 36 to 66 % of the plant species at each site. To evaluate the status and trends of common, rare, and exotic plant species at local, regional, and national scales, innovative, multi-scale methods must replace the commonly used transect methods to the past.

Journal of Range Management↗

USGS2014

Biological soil crusts (biocrusts) as a model system in community, landscape and ecosystem ecology

Model systems have had a profound influence on the development of ecological theory and general principles. Compared to alternatives, the most effective models share some combination of the following characteristics: simpler, smaller, faster, general, idiosyncratic or manipulable. We argue that biological soil crusts (biocrusts) have unique combinations of these features that should be more widely exploited in community, landscape and ecosystem ecology. In community ecology, biocrusts are elucidating the importance of biodiversity and spatial pattern for maintaining ecosystem multifunctionality due to their manipulability in experiments. Due to idiosyncrasies in their modes of facilitation and competition, biocrusts have led to new models on the interplay between environmental stress and biotic interactions and on the maintenance of biodiversity by competitive processes. Biocrusts are perhaps one of the best examples of micro-landscapes—real landscapes that are small in size. Although they exhibit varying patch heterogeneity, aggregation, connectivity and fragmentation, like macro-landscapes, they are also compatible with well-replicated experiments (unlike macro-landscapes). In ecosystem ecology, a number of studies are imposing small-scale, low cost manipulations of global change or state factors in biocrust micro-landscapes. The versatility of biocrusts to inform such disparate lines of inquiry suggests that they are an especially useful model system that can enable researchers to see ecological principles more clearly and quickly.

Biodiversity and Conservation↗

USGS2015

Global patterns and environmental controls of perchlorate and nitrate co-occurrence in arid and semi-arid environments

Natural perchlorate (ClO 4 − ) is of increasing interest due to its wide-spread occurrence on Earth and Mars, yet little information exists on the relative abundance of ClO 4 − compared to other major anions, its stability, or long-term variations in production that may impact the observed distributions. Our objectives were to evaluate the occurrence and fate of ClO 4 − in groundwater and soils/caliche in arid and semi-arid environments (southwestern United States, southern Africa, United Arab Emirates, China, Antarctica, and Chile) and the relationship of ClO 4 − to the more well-studied atmospherically deposited anions NO 3 − and Cl − as a means to understand the prevalent processes that affect the accumulation of these species over various time scales. ClO 4 − is globally distributed in soil and groundwater in arid and semi-arid regions on Earth at concentrations ranging from 10 −1 to 10 6 μg/kg. Generally, the ClO 4 − concentration in these regions increases with aridity index, but also depends on the duration of arid conditions. In many arid and semi-arid areas, NO 3 − and ClO 4 − co-occur at molar ratios (NO 3 − /ClO 4 − ) that vary between ∼10 4 and 10 5 . We hypothesize that atmospheric deposition ratios are largely preserved in hyper-arid areas that support little or no biological activity (e.g. plants or bacteria), but can be altered in areas with more active biological processes including N 2 fixation, N mineralization, nitrification, denitrification, and microbial ClO 4 − reduction, as indicated in part by NO 3 − isotope data. In contrast, much larger ranges of Cl − /ClO 4 − and Cl − /NO 3 − ratios indicate Cl − varies independently from both ClO 4 − and NO 3 − . The general lack of correlation between Cl − and ClO 4 − or NO 3 − implies that Cl − is not a good indicator of co-deposition and should be used with care when interpreting oxyanion cycling in arid systems. The Atacama Desert appears to be unique compared to all other terrestrial locations having a NO 3 − /ClO 4 − molar ratio ∼10 3 . The relative enrichment in ClO 4 − compared to Cl − or NO 3 − and unique isotopic composition of Atacama ClO 4 − may reflect either additional in-situ production mechanism(s) or higher relative atmospheric production rates in that specific region or in the geological past. Elevated concentrations of ClO 4 − reported on the surface of Mars, and its enrichment with respect to Cl − and NO 3 − , could reveal important clues regarding the climatic, hydrologic, and potentially biologic evolution of that planet. Given the highly conserved ratio of NO 3 − /ClO 4 − in non-biologically active areas on Earth, it may be possible to use alterations of this ratio as a biomarker on Mars and for interpreting major anion cycles and processes on both Mars and Earth, particularly with respect to the less-conserved NO 3 − pool terrestrially.

Geochimica et Cosmochimica Acta↗

USGS1995

Effects of agricultural land-management practices on water quality in northeastern Guilford County, North Carolina, 1985-90

The effects of selected agricultural land-management practices on water quality were assessed in a comparative study of four small basins in the Piedmont province of North Carolina. Agricultural practices, such as tillage and applications of fertilizer and pesticides, are major sources of sediment, nutrients, and pesticides in surface water, and of nutrients and pesticides in ground water. The four study basins included two adjacent row-crop fields, a mixed land-use basin, and a forested basin. One of the row-crop fields (7.4 acres) was farmed by using conservation land-management (CLM) practices, which included strip cropping, contour plowing, field borders, and grassed waterways. The other row-crop field (4.8 acres) was farmed by using standard land-management (SLM) practices, which included continuous cropping, straight-row plowing without regard to land topography, and poorly maintained waterways. The mixed land-use basin (665 acres) was monitored to compare water quality in surface water as SLM practices were converted to CLM practices during the project. The forested basin (44 acres) provided background surface-water hydrologic and chemical-quality conditions. Surface-water flow was reduced by 18 percent by CLM practices compared to surface-water flow from the SLM practices basin. The thickness of the unsaturated zone in the row-crop basins ranged from a few feet to 25 feet. Areas with thick unsaturated zones have a greater capacity to intercept and store nutrients and pesticides than do areas with thinner zones. Sediment concentrations and yields for the SLM practices basin were considerably higher than those for the other basins. The median sediment concentration in surface water for the SLM basin was 3.4 times that of the CLM basin, 8.2 times that of the mixed land-use basin, and 38.4 times that of the forested basin. The total sediment yield for the SLM basin was 2.3 times that observed for the CLM basin, 14.1 times that observed for the mixed land-use basin, and 19.5 times the yield observed for the forested basin. Nutrient concentrations in surface water from the row-crop and mixed land-use basins were higher than those measured in the forested basin and in precipitation collected near the row-crop basins. The SLM basin generally had the highest concentrations of total nitrogen, nitrite plus nitrate, total phosphorus (equivalent to the mixed land-use basin), and potassium. Nutrient concentrations in soil water and ground water were less than concentrations in surface water for the row-crop basins. Nutrient concentrations generally were at least slightly below the root zone (3-foot depth) and in ground water. Differences in nutrient yields among basins had patterns similar to those observed for nutrient concentrations. The total nitrogen yield for the SLM basin was 1.2 times the yield for the CLM basin, 1.9 times the yield for the mixed land-use basin, and 4.2 times the yield for the forested basin. The total phosphorus yield for the SLM basin was 1.7 times the yield for the CLM basin, 3.3 times the yield for the mixed land-use basin, and 7.8 times the yield for the forested basin. No significant differences in pesticide concentrations in surface water were identified between those measured in the SLM basin and those measured in the CLM basin. Significantly higher pesticide concentrations were observed at the row-crop basins compared with those observed at the mixed land-use basin probably because sampling sites for the row-crop basins were closer to the pesticide sources. No pesticides were detected in the forested basin. Comparisons of pesticide concentrations in soil from the two row-crop basins indicated some differences. Concentrations of the soil pesticides isopropalin and flumetralin were higher in the SLM basin than in the CLM basin. The surface-water quality of the mixed land-use basin generally was less affected by agricultural nonpoint sources than that of the smaller row-crop b

North Carolina↗

USGS1940

Geology and ground-water resources of the islands of Lanai and Kahoolawe, Hawaii

Lanai lies 59 miles southeast of Honolulu, Oahu, has an area of 141 square miles, and is 3,370 feet high. (See fig. 1 and pl. 1.) Lanai City is the only town of importance. The island produces pineapples and cattle. The surface above about 1,200 feet is generally covered with lateritic soil, which reaches a maximum depth of about 50 feet. Below this level the island is partly devoid of vegetation and is strewn with boulders, the result of having been once submerged by the ocean to this depth. Traces of various emerged and submerged shore lines are described, the highest fossiliferous marine deposits being 1,070 feet above sea level. Lanai is an eroded extinct basaltic volcano built during one period of activity. No secondary eruptions occurred as on most of the other islands. It has three rift zones and a summit caldera. The summit plateau has resulted from collapse along the northwest rift zone. Elsewhere there is much evidence of faulting. About 100 faults and 275 dikes were recorded, but they are so close together in places that it was not possible to show them all on the map. The climate is semitropical, the mean annual temperature of Lanai City, altitude 1,620 feet, being 68° F. Because Lanai lies to the lee of Maui Island it is dry. The mean annual rainfall ranges from 38 inches on the summit to less than 10 inches on the coast. The windward (northeast) side is carved by streams into deep canyons. Maunalei Gulch has the only perennial stream, and it does not reach the sea. Ground water, the lifeblood of Lanai is scarce. Lanai City obtains some of its water supply by a tunnel from gravel in Maumalei Gulch. This water apparently rises from the dike complex in this gulch. The rest of the supply comes from a recently constructed shaft tapping the dike complex not far downstream. The total quantity of high-level ground water discharged by springs and tunnels ranges from about 600,000 gallons a day in wet weather to about 250,000 gallons a day in dry weather. The basal water, although potable, is fairly high in salt. Several sites are recommended for developing and conserving ground water. Kahoolawe Island is 11 miles long, 6 miles wide, 1,491 feet high, covers 45 square miles, and lies 94 miles southeast of Honolulu and 6 3 / 4 miles southwest of Maui. It is a shield-shaped extinct volcano composed chiefly of thin flows of primitive basalt poured in rapid succession from three rift zones and a vent at their intersection. At one stage the volcano was indented with a caldera about 3 miles across which was later completely filled. A graben led southwestward from it. The rocks are divided into Late Tertiary (?) or early Pleistocene(?) pre-caldera basalts, caldera-filling basalts and basaltic andesites, post-caldera basalts and andesites, and Recent post erosional basalts. A few thin vitric tuff beds and cinder cones were found. Marine erosion has cut cliffs as high as 800 feet along the east and south shores and exposed a cross section of the caldera. Only shallow ephemeral gulches exist. The entire summit has been eroded to a hard-pan surface by the wind as a result of the vegetation being destroyed by livestock. The island is semi-arid and well water is needed for stook: "The stook is now supplied entirely from storage of rain and flood waters. During droughts water is hauled by boat from the island of Maui. All the wells dug so far yield water that is too brackish for stock except at the fairly inaccessible south side of Kanapou Bay. The resistivity survey indicates a water table 1.5 feet or less above sea level for 2.25 miles inland. A few sites for wells are recommended in the dike complex where small supplies of water suitable for stock might be found. Petrographic studies by Gordon A. Macdonald indicate that the pre-caldera and caldera-filling lavas are largely normal olivine basalt of the type which forms the bulk of all Hawaiian volcanoes thus far investigated. It represents the undifferentiated magma of the Hawaiian petrographic province. Toward the close of the caldera-filling epoch the vent became less active, and magmatic differentiation produced basaltic andesites, which are interbedded with normal basalts. The post-caldera lavas are largely basaltic andesites and andesites. The much younger lavas, erupted after a period of extensive erosion, are olivine basalts similar in composition to the pre-caldera flows. The mineralogy of the Kahoolawe rocks is described in detail.

Hawaii↗

USGS2010

Sedimentation, sediment quality, and upstream channel stability, John Redmond Reservoir, east-central Kansas, 1964-2009

A combination of available bathymetric-survey information, bottom-sediment coring, and historical streamgage information was used to investigate sedimentation, sediment quality, and upstream channel stability for John Redmond Reservoir, east-central Kansas. Ongoing sedimentation is reducing the ability of the reservoir to serve several purposes including flood control, water supply, and recreation. The total estimated volume and mass of bottom sediment deposited between 1964 and 2009 in the conservation pool of the reservoir was 1.46 billion cubic feet and 55.8 billion pounds, respectively. The estimated sediment volume occupied about 41 percent of the conservation-pool, water-storage capacity of the reservoir. Water-storage capacity in the conservation pool has been lost to sedimentation at a rate of about 1 percent annually. Mean annual net sediment deposition since 1964 in the conservation pool of the reservoir was estimated to be 1.24 billion pounds per year. Mean annual net sediment yield from the reservoir basin was estimated to be 411,000 pounds per square mile per year Information from sediment cores shows that throughout the history of John Redmond Reservoir, total nitrogen concentrations in the deposited sediment generally were uniform indicating consistent nitrogen inputs to the reservoir. Total phosphorus concentrations in the deposited sediment were more variable than total nitrogen indicating the possibility of changing phosphorus inputs to the reservoir. As the principal limiting factor for primary production in most freshwater environments, phosphorus is of particular importance because increased inputs can contribute to accelerated reservoir eutrophication and the production of algal toxins and taste-and-odor compounds. The mean annual net loads of total nitrogen and total phosphorus deposited in the bottom sediment of the reservoir were estimated to be 2,350,000 pounds per year and 1,030,000 pounds per year, respectively. The estimated mean annual net yields of total nitrogen and total phosphorus from the reservoir basin were 779 pounds per square mile per year and 342 pounds per square mile per year, respectively. Trace element concentrations in the bottom sediment of John Redmond Reservoir generally were uniform over time. As is typical for eastern Kansas reservoirs, arsenic, chromium, and nickel concentrations typically exceeded the threshold-effects guidelines, which represent the concentrations above which toxic biological effects occasionally occur. Trace element concentrations did not exceed the probable-effects guidelines (available for eight trace elements), which represent the concentrations above which toxic biological effects usually or frequently occur. Organochlorine compounds either were not detected or were detected at concentrations that were less than the threshold-effects guidelines. Stream channel banks, compared to channel beds, likely are a more important source of sediment to John Redmond Reservoir from the upstream basin. Other sediment sources include surface-soil erosion in the basin and shoreline erosion in the reservoir.

Scientific Investigations Report↗

USGS2016

Changing regional emissions of airborne pollutants reflected in the chemistry of snowpacks and wetfall in the Rocky Mountain region, USA, 1993–2012

Wintertime precipitation sample data from 55 Snowpack sites and 17 National Atmospheric Deposition Program (NADP)/National Trends Network Wetfall sites in the Rocky Mountain region were examined to identify long-term trends in chemical concentration, deposition, and precipitation using Regional and Seasonal Kendall tests. The Natural Resources Conservation Service snow-telemetry (SNOTEL) network provided snow-water-equivalent data from 33 sites located near Snowpack- and NADP Wetfall-sampling sites for further comparisons. Concentration and deposition of ammonium, calcium, nitrate, and sulfate were tested for trends for the period 1993–2012. Precipitation trends were compared between the three monitoring networks for the winter seasons and downward trends were observed for both Snowpack and SNOTEL networks, but not for the NADP Wetfall network. The dry-deposition fraction of total atmospheric deposition, relative to wet deposition, was shown to be considerable in the region. Potential sources of regional airborne pollutant emissions were identified from the U.S. Environmental Protection Agency 2011 National Emissions Inventory, and from long-term emissions data for the period 1996–2013. Changes in the emissions of ammonia, nitrogen oxides, and sulfur dioxide were reflected in significant trends in snowpack and wetfall chemistry. In general, ammonia emissions in the western USA showed a gradual increase over the past decade, while ammonium concentrations and deposition in snowpacks and wetfall showed upward trends. Emissions of nitrogen oxides and sulfur dioxide declined while regional trends in snowpack and wetfall concentrations and deposition of nitrate and sulfate were downward.

Colorado, Idaho, Montana, New Mexico, Utah, Wyomin↗

USGS2012

A brief history and summary of the effects of river engineering and dams on the Mississippi River system and delta

The U.S. Geological Survey Forecast Mekong project is providing technical assistance and information to aid management decisions and build science capacity of institutions in the Mekong River Basin. A component of this effort is to produce a synthesis of the effects of dams and other engineering structures on large-river hydrology, sediment transport, geomorphology, ecology, water quality, and deltaic systems. The Mississippi River Basin (MRB) of the United States was used as the backdrop and context for this synthesis because it is a continental scale river system with a total annual water discharge proportional to the Mekong River, has been highly engineered over the past two centuries, and the effects of engineering have been widely studied and documented by scientists and engineers. The MRB is controlled and regulated by dams and river-engineering structures. These modifications have resulted in multiple benefits including navigation, flood control, hydropower, bank stabilization, and recreation. Dams and other river-engineering structures in the MRB have afforded the United States substantial socioeconomic benefits; however, these benefits also have transformed the hydrologic, sediment transport, geomorphic, water-quality, and ecologic characteristics of the river and its delta. Large dams on the middle Missouri River have substantially reduced the magnitude of peak floods, increased base discharges, and reduced the overall variability of intraannual discharges. The extensive system of levees and wing dikes throughout the MRB, although providing protection from intermediate magnitude floods, have reduced overall channel capacity and increased flood stage by up to 4 meters for higher magnitude floods. Prior to major river engineering, the estimated average annual sediment yield of the Mississippi River Basin was approximately 400 million metric tons. The construction of large main-channel reservoirs on the Missouri and Arkansas Rivers, sedimentation in dike fields, and protection of channel banks by revetments throughout the basin, have reduced the overall sediment yield of the MRB by more than 60 percent. The primary alterations to channel morphology by dams and other engineering projects have been (1) channel simplification and reduced dynamism; (2) lowering of channel-bed elevation; and (3) disconnection of the river channel from the flood plain, except during extreme flood events. Freshwater discharge from the Mississippi River and its associated sediment and nutrient loads strongly influence the physical and biological components in the northern Gulf of Mexico. Ninety percent of the nitrogen load reaching the Gulf of Mexico is from nonpoint sources with about 60 percent coming from fertilizer and mineralized soil nitrogen. Much of the phosphorus is from animal manure from pasture and rangelands followed by fertilizer applied to corn and soybeans. Increased nutrient enrichment in the northern Gulf of Mexico has resulted in the degradation of water quality as more phytoplankton grow, which increases turbidity and depletes oxygen in the lower depths creating what is known as the "dead zone." In 2002, the dead zone was 22,000 square kilometers (km2), an area similar to the size of the State of Massachusetts. Changes in the flow regime from engineered structures have had direct and indirect effects on the fish communities. The navigation pools in the upper Mississippi River have aged, and these overwintering habitats, which were created when the pools filled, have declined as sedimentation reduces water depth. Reproduction of paddlefish may have been adversely affected by dams, which impede access to suitable spawning habitats. Fishes that inhabit swift-current habitats in the unimpounded lower Mississippi River have not declined as much as in the upper Mississippi River. The decline of the pallid sturgeon may be attributable to channelization of the Missouri River above St. Louis, Missouri. The Missouri River supports a rich fish community and remains relatively intact. Nevertheless, the widespread and long history of human intervention in river discharge has contributed to the declines of about 25 percent of the species. The Mississippi River Delta Plain is built from six delta complexes composed of a massive area of coastal wetlands that support the largest commercial fishery in the conterminous United States. Since the early 20th century, approximately 4,900 km2 of coastal lands have been lost in Louisiana. One of the primary mechanisms of wetland loss on the Plaquemines-Balize complex is believed to be the disconnection of the river distributary network from the delta plain by the massive system of levees on the delta top, which prevent overbank flooding and replenishment of the delta top by sediment and nutrient deliveries. Efforts by Federal and State agencies to conserve and restore the Mississippi River Delta Plain began over three decades ago and have accelerated over the past decade. Regardless of these efforts, however, land losses are expected to continue because the reduced upstream sediment supplies are not sufficient to keep up with the projected depositional space being created by the combined forces of delta plain subsidence and global sea-level rise.

Alabama;Alberta;Arkansas;Colorado;Georgia;Illinois↗

USGS1964

Use of ground-water reservoirs for storage of surface water in the San Joaquin Valley, California

The San Joaquin Valley includes roughly the southern two-thirds of the Central Valley of California, extending 250 miles from Stockton on the north to Grapevine at the foot of the Tehachapi Mountains. The valley floor ranges in width from 25 miles near Bakersfield to about 55 miles near Visalia; it has a surface area of about 10,000 square miles. More than one-quarter of all the ground water pumped for irrigation in the United States is used in this highly productive valley. Withdrawal of ground water from storage by heavy pumping not only provides a needed irrigation water supply, but it also lowers the ground-water level and makes storage space available in which to conserve excess water during periods of heavy runoff. A storage capacity estimated to be 93 million acre-feet to a depth of 200 feet is available in this ground-water reservoir. This is about nine times the combined capacity of the existing and proposed surface-water reservoirs in the San Joaquin Valley under the California Water Plan. The landforms of the San Joaquin Valley include dissected uplands, low plains and fans, river flood plains and channels, and overflow lands and lake bottoms. Below the land surface, unconsolidated sediments derived from the surrounding mountain highlands extend downward for hundreds of feet. These unconsolidated deposits, consisting chiefly of alluvial deposits, but including some widespread lacustrine sediments, are the principal source of ground water in the valley. Ground water occurs under confined and unconfined conditions in the San Joaquin Valley. In much of the western, central, and southeastern parts of the valley, three distinct ground-water reservoirs are present. In downward succession these are 1) a body of unconfined and semiconfined fresh water in alluvial deposits of Recent, Pleistocene, and possibly later Pliocene age, overlying the Corcoran clay member of the Tulare formation; 2) a body of fresh water confined beneath the Corcoran clay member, which occurs in alluvial and lacustrine deposits of late Pliocene age or older; and 3) a body of saline connate water contained in marine sediments of middle Pliocene or older age, which underlies the fresh-water body throughout the area. In much of the eastern part of the valley, especially in the areas of the major streams, the Corcoran clay member is not present and ground water occurs as one fresh-water body to considerable depth. The ground-water body is replenished by infiltration of rainfall, by infiltration from streams, canals, and ditches, by underflow entering the valley from tributary stream canyons, and by infiltration of excess irrigation water. In much of the valley, however, the annual rainfall is so low that little penetrates deeply, and soil-moisture deficiency is perennial. Infiltration from stream channels and canals and from irrigated fields are the principal sources of groundwater recharge. The ground-water storage capacity of the San Joaquin Valley has been estimated in an earlier report (Davis and others, 1959) as 93 million acre-feet. This is the quantity of water that would drain by gravity from the valley deposits if the regional water level were lowered from 10 to 200 feet below the land surface. Storage capacity was estimated for only the part of the valley considered to be potentially usable as a ground-water reservoir. In this study, a 200foot depth was selected as a practical valley-wide depth limit for unwatering under full utilization of the ground-water reservoir, even though in localized areas sections in excess of 350 feet in depth have already been dewatered. Some of the factors that locally limit the utilization of the ground-water reservoir are inferior water quality, relatively impermeable surface soils, and relatively impermeable subsurface deposits. On the basis of a detailed analysis of la peg model, the subsurface geology of the San Joaquin Valley was subdivided into predominantly permeable and impermeable zones in the 1

Water Supply Paper↗

USGS2014

Regional regression equations for the estimation of selected monthly low-flow duration and frequency statistics at ungaged sites on streams in New Jersey

Regional regression equations were developed for estimating monthly flow-duration and monthly low-flow frequency statistics for ungaged streams in Coastal Plain and non-coastal regions of New Jersey for baseline and current land- and water-use conditions. The equations were developed to estimate 87 different streamflow statistics, which include the monthly 99-, 90-, 85-, 75-, 50-, and 25-percentile flow-durations of the minimum 1-day daily flow; the August–September 99-, 90-, and 75-percentile minimum 1-day daily flow; and the monthly 7-day, 10-year (M7D10Y) low-flow frequency. These 87 streamflow statistics were computed for 41 continuous-record streamflow-gaging stations (streamgages) with 20 or more years of record and 167 low-flow partial-record stations in New Jersey with 10 or more streamflow measurements. The regression analyses used to develop equations to estimate selected streamflow statistics were performed by testing the relation between flow-duration statistics and low-flow frequency statistics for 32 basin characteristics (physical characteristics, land use, surficial geology, and climate) at the 41 streamgages and 167 low-flow partial-record stations. The regression analyses determined drainage area, soil permeability, average April precipitation, average June precipitation, and percent storage (water bodies and wetlands) were the significant explanatory variables for estimating the selected flow-duration and low-flow frequency statistics. Streamflow estimates were computed for two land- and water-use conditions in New Jersey—land- and water-use during the baseline period of record (defined as the years a streamgage had little to no change in development and water use) and current land- and water-use conditions (1989–2008)—for each selected station using data collected through water year 2008. The baseline period of record is representative of a period when the basin was unaffected by change in development. The current period is representative of the increased development of the last 20 years (1989–2008). The two different land- and water-use conditions were used as surrogates for development to determine whether there have been changes in low-flow statistics as a result of changes in development over time. The State was divided into two low-flow regression regions, the Coastal Plain and the non-coastal region, in order to improve the accuracy of the regression equations. The left-censored parametric survival regression method was used for the analyses to account for streamgages and partial-record stations that had zero flow values for some of the statistics. The average standard error of estimate for the 348 regression equations ranged from 16 to 340 percent. These regression equations and basin characteristics are presented in the U.S. Geological Survey (USGS) StreamStats Web-based geographic information system application. This tool allows users to click on an ungaged site on a stream in New Jersey and get the estimated flow-duration and low-flow frequency statistics. Additionally, the user can click on a streamgage or partial-record station and get the “at-site” streamflow statistics. The low-flow characteristics of a stream ultimately affect the use of the stream by humans. Specific information on the low-flow characteristics of streams is essential to water managers who deal with problems related to municipal and industrial water supply, fish and wildlife conservation, and dilution of wastewater.

New Jersey↗

USGS2009

Characteristics of the April 2007 Flood at 10 Streamflow-Gaging Stations in Massachusetts

A large 'nor'easter' storm on April 15-18, 2007, brought heavy rains to the southern New England region that, coupled with normal seasonal high flows and associated wet soil-moisture conditions, caused extensive flooding in many parts of Massachusetts and neighboring states. To characterize the magnitude of the April 2007 flood, a peak-flow frequency analysis was undertaken at 10 selected streamflow-gaging stations in Massachusetts to determine the magnitude of flood flows at 5-, 10-, 25-, 50-, 100-, 200-, and 500-year return intervals. The magnitude of flood flows at various return intervals were determined from the logarithms of the annual peaks fit to a Pearson Type III probability distribution. Analysis included augmenting the station record with longer-term records from one or more nearby stations to provide a common period of comparison that includes notable floods in 1936, 1938, and 1955. The April 2007 peak flow was among the highest recorded or estimated since 1936, often ranking between the 3d and 5th highest peak for that period. In general, the peak-flow frequency analysis indicates the April 2007 peak flow has an estimated return interval between 25 and 50 years; at stations in the northeastern and central areas of the state, the storm was less severe resulting in flows with return intervals of about 5 and 10 years, respectively. At Merrimack River at Lowell, the April 2007 peak flow approached a 100-year return interval that was computed from post-flood control records and the 1936 and 1938 peak flows adjusted for flood control. In general, the magnitude of flood flow for a given return interval computed from the streamflow-gaging station period-of-record was greater than those used to calculate flood profiles in various community flood-insurance studies. In addition, the magnitude of the updated flood flow and current (2008) stage-discharge relation at a given streamflow-gaging station often produced a flood stage that was considerably different than the flood stage indicated in the flood-insurance study flood profile at that station. Equations for estimating the flow magnitudes for 5-, 10-, 25-, 50-, 100-, 200-, and 500-year floods were developed from the relation of the magnitude of flood flows to drainage area calculated from the six streamflow-gaging stations with the longest unaltered record. These equations produced a more conservative estimate of flood flows (higher discharges) than the existing regional equations for estimating flood flows at ungaged rivers in Massachusetts. Large differences in the magnitude of flood flows for various return intervals determined in this study compared to results from existing regional equations and flood insurance studies indicate a need for updating regional analyses and equations for estimating the expected magnitude of flood flows in Massachusetts.

Scientific Investigations Report↗

USGS2011

Recent (2008-10) concentrations and isotopic compositions of nitrate and concentrations of wastewater compounds in the Barton Springs zone, south-central Texas, and their potential relation to urban development in the contributing zone

During 2008–10, the U.S. Geological Survey, in cooperation with the City of Austin, the City of Dripping Springs, the Barton Springs/Edwards Aquifer Conservation District, the Lower Colorado River Authority, Hays County, and Travis County, collected and analyzed water samples from five streams (Barton, Williamson, Slaughter, Bear, and Onion Creeks), two groundwater wells (Marbridge well [YD–58–50–704] and Buda well [LR–58–58–403]), and the main orifice of Barton Springs in Austin, Texas, with the objective of characterizing concentrations and isotopic compositions of nitrate and concentrations of wastewater compounds in the Barton Springs zone. The Barton Springs zone is in south-central Texas, an area undergoing rapid growth in population and in land area affected by development, with associated increases in wastewater generation. Over a period of 17 months, during which the hydrologic conditions transitioned from dry to wet, samples were collected routinely from the streams, wells, and spring and, in response to storms, from the streams and spring; some or all samples were analyzed for nitrate, nitrogen and oxygen isotopes of nitrate, and wastewater compounds. The median nitrate concentrations in routine samples from all sites were higher in samples collected during the wet period than in samples collected during the dry period, with the greatest difference for stream samples (0.05 milligram per liter during the dry period to 0.96 milligram per liter for the wet period). Nitrate concentrations in recent (2008–10) samples were elevated relative to concentrations in historical (1990–2008) samples from streams and from Barton Springs under medium- and high-flow conditions. Recent nitrate concentrations were higher than historical concentrations at the Marbridge well but the reverse was true at the Buda well. The elevated concentrations likely are related to the cessation of dry conditions coupled with increased nitrogen loading in the contributing watersheds. An isotopic composition of nitrate (delta nitrogen–15) greater than 8 per mil in many of the samples indicated there was a contribution of nitrate with a biogenic (human and or animal waste, or both) origin. Wastewater compounds measured in routine samples were detected infrequently (3 percent of cases), and concentrations were very low (less than the method reporting level in most cases). There was no correlation between nitrate concentrations and the frequency of detection of wastewater compounds, indicating that wastewater compounds might be undergoing removal during such processes as infiltration through soil. Three potential sources of biogenic nitrate to the contributing zone were considered: septic systems, land application of treated wastewater, and domesticated dogs and cats. During 2001–10, the estimated densities of septic systems and domesticated dogs and cats (number per acre) increased in the watersheds of all five creeks, and the rate of land application of treated wastewater (gallons per day per acre) increased in the watersheds of Barton, Bear, and Onion Creeks. Considering the timing and location of the increases in the three sources, septic systems were considered a likely source of increased nitrate to Bear Creek; land application of treated wastewater a likely source to Barton, Bear, and Onion Creeks; and domestic dogs and cats a potential source principally to Williamson Creek. The results of this investigation indicate that baseline water quality, in terms of nitrate, has shifted upward between 2001 and 2010, even without any direct discharges of treated wastewater to the creeks.

Texas↗

USGS2010

Herbicide treatment of invasive Vinca major growing with endangered Galium buxifolium, an island endemic

Galium buxifolium E. Greene [Rubiaceae] (sea-cliff bedstraw) is a small shrub restricted to San Miguel and Santa Cruz Islands, in the California Channel Islands. Almost all of the 26 known populations grow on vertical north-facing sea cliffs in native scrub, sandwiched between the sea below and non-native annual grasslands on the terraces above. A notable exception is a popula?tion at Pelican Bay on Santa Cruz Island, growing on the cliff and on thin terrace soils above the cliff in a stand of coastal bluff scrub that is recovering from more than a century of sheep grazing (Figure 1). Ironically, this stand is near the location of the historic Eaton Resort, a charismatic inn frequented by Hollywood glitterati in the early 1900s. Several landscape ornamentals planted there persist today in the area of the Galium population. Italian stone pine (Pinus pinaea) and eucalyptus (Eucalyptus spp.) tower over the site while the invasive groundcover Vinca major L. [Apocynaceae] (greater periwinkle) forms dense mats at the cliff edge that are spreading into the developing native plant stand. Wherever the Galium is found it is intermixed with other native scrub plants in dense communities on moist ocean bluffs. Historic notes and herbarium collections indicate that it may have been more widespread on nearshore terraces adjacent to sea-cliff populations before conversion to grassland. Since Pelican Bay is the only site that we know of where Galium is spreading onto the nearby terrace, we wanted to know whether the Vinca posed a roadblock to upslope population expansion. In 2005 we mapped Vinca and Galium at the site. We also measured Galium individuals to see where the smaller, younger plants were to better understand where the population is expanding. We observed that 1) both the Galium and the Vinca appear to be spreading from the cliff face upslope onto a series of rock outcrops, stone walls and benches, 2) the native scrub community is recovering at the site and 3) the Vinca appears to be moving into the native scrub where it overtops small plants, including those Galium in the smallest size classes. This observed pattern of Vinca displacement of native vegetation has been noted in other places, where it is treated as an invasive weed. We concluded that Vinca may pose a threat to the expansion of both the native scrub and the Galium population that it supports. Therefore, we worked with the US Fish and Wildlife Service and others to develop a research project investigating 1) best techniques for killing Vinca within the boundaries of an endangered plant population and 2) demographic response of Galium to the treatment. Our intent is to push Vinca back to the vertical cliff face to give the natives a chance to establish a vigorous stand. Our conservation goal is to encourage natural establishment of new Galium plants on the terrace along with expansion of the native coastal bluff scrub and Galium population. Our immediate treatment objective is to reduce live Vinca cover by 90 % on the accessible upslope portions of the habitat. Our recovery objective is no net loss of Galium plants 2006-2016.

California↗

USGS2019

Sea-cliff bedstraw (Galium buxifolium) patterns and trends, 2005–14, on Santa Cruz and San Miguel Islands, Channel Islands National Park, California

Sea-cliff bedstraw (Galium buxifolium [Rubiaceae]) is a delicate dioecious subshrub endemic to Santa Cruz and San Miguel Islands, in the northern California Channel Islands. It was listed as endangered in 1997 under the Federal Endangered Species Act, threatened by soil loss, habitat alteration, and herbivory from more than a century of ranching land use. At the time of listing, there were eight populations known from Santa Cruz Island and two from San Miguel Island, restricted to shaded, northfacing volcanic ocean bluffs. The recovery plan included criteria to be considered for delisting such as stabilizing or increasing populations on both islands and recovery actions such as searching for more populations, seed banking, researching seed germination and life history, and reversing factors causing decline. We began studying sea-cliff bedstraw on Santa Cruz Island in the early 2000s to better understand factors related to decline. We surveyed historic populations and searched for new occurrences 2004–06, researched population size-class structure and floral biology 2005–06 at three sites, and tracked demography 2005–14 while treating the invasive periwinkle ( Vinca major ) with herbicide at a fourth site. We collected seeds for germination studies and long-term seed banking from all four study sites. The historically known Santa Cruz Island sites were still extant on the sea-cliffs, and we located 14 occurrences not documented at the time of listing. Sea-cliff bedstraw floral morphology appears evenly balanced between mainly pistillate and staminate plants at the study sites, with other floral types present as well, in the populations we sampled. Seed germination trials showed about a 40 percent germination rate from fresh imbibed seeds. Life-history stage structure 2005–06 varied from purely reproductive plants at one site to nearly equal representation of vegetative and reproductive plants at a second site, with seedlings also present at the remaining two sites. Demographic study of tagged plants at the long-term study plot 2005–14 showed an episodic pattern of high recruitment with low mortality once plants became established beyond the first summer dormant season. A flush of seedlings was seen after periwinkle reduction, indicating that the periwinkle may have been repressing seedling establishment. About 93 percent of the already-established plants tagged in 2005 and 2006 were still present 10 years later in 2014. Findings indicate that sea-cliff bedstraw individuals are long-lived and once established have good survival rates. Taken together, these results imply that population growth is driven more by germination and recruitment into the mature population than by mortality of established plants, at least since feral animal eradication from Santa Cruz Island. Therefore, conservation actions might be best focused on nurturing safe sites for seed germination and seedling survival.

California↗

USGS2023

Integrated rangeland fire management strategy actionable science plan completion assessment: Restoration topic, 2015–20

Loss and degradation of sagebrush rangelands due to an accelerated invasive annual grass-wildfire cycle and other stressors are substantial management, conservation, and economic issues in the western United States. These sagebrush rangelands comprise a unique biome spanning 11 states, support over 350 wildlife species, and provide important ecosystem services that include stabilizing the economies of western communities. Impacts to sagebrush ecosystem processes over large areas due to the annual grass-wildfire cycle necessitated the development of a coordinated, science-based strategy for improving efforts to achieve long-term protection, conservation, and restoration of sagebrush rangelands, which was framed in 2015 under the Integrated Rangeland Fire Management Strategy (IRFMS). Central to this effort was the development of an Actionable Science Plan (Plan) that identified 37 priority science needs (Needs) for informing the actions proposed under the 5 topics (Fire, Invasives, Restoration, Sagebrush and Sage-Grouse, Climate and Weather) that were part of the collective focus of the IRFMS. Notable keys to this effort were identification of the Needs co-produced by managers and researchers, and a focus on resulting science being “actionable.” Substantial investments aimed at fulfilling the Needs identified in the Plan have been made since its release in 2016. While the state of the science has advanced considerably, the extent to which knowledge gaps remain relative to identified Needs is relatively unknown. Moreover, new Needs have likely emerged since the original strategy as results from actionable science reveal new questions, and possible (yet untested) solutions. A quantifiable assessment of the progress made on the original science Needs can identify unresolved gaps and new information that can help inform prioritization of future research efforts. This report details a systematic literature review that evaluated how well peer-reviewed journal articles and formal technical reports published between January 1, 2015, and December 31, 2020, addressed 10 needs (hereinafter “Needs”) identified under the Restoration topic in the Plan. The topic outlined research Needs for improving restoration success in degraded sagebrush rangelands. We established the level of progress towards addressing each Need following a standardized set of criteria, and developed summaries detailing how research objectives nested within Needs identified in the Plan (“Next Steps”) were either addressed well, partially addressed or remain outstanding (that is, addressed poorly) in the literature through 2020. Our searches resulted in the inclusion of 371 science products that at least partially addressed a Need identified in the Restoration topic. The Needs that were well and partially addressed included: the development of methods to improve seeding success of native plants after fire; evaluation of short- and long-term plant responses relative to biotic and abiotic factors following restoration treatments; assessments of long-term effects on ecosystem processes following conifer removal treatments and development of decision support tools to aid in conifer management; determination of the costs of restoration treatments relative to the benefits to sage-grouse occupancy, survival, and populations; and assessments of the factors which contribute to soil degradation and development of soil enhancement methods that enhance seed germination and seedling survival while resisting nonnative plants. Needs that were not addressed well included: the development of methods for the rapid recovery of sagebrush and native herbaceous plants following wildfire and determination of whether treatments benefit sage-grouse and mitigate impacts from fires; determination of thresholds for successful restoration across a range of environmental conditions and development of decision support tools to assist with restoration effectiveness monitoring; and development and evaluation of the utility of seed transfer zones. The information provided in this assessment will assist updating the Plan along with other science strategies.

western United States↗

USGS2008

Salinity trends in the upper Colorado River basin upstream from the Grand Valley Salinity Control Unit, Colorado, 1986-2003

In 1974, the Colorado River Basin Salinity Control Act was passed into law. This law was enacted to address concerns regarding the salinity content of the Colorado River. The law authorized various construction projects in selected areas or "units" of the Colorado River Basin intended to reduce the salinity load in the Colorado River. One such area was the Grand Valley Salinity Control Unit in western Colorado. The U. S. Geological Survey has done extensive studies and research in the Grand Valley Salinity Control Unit that provide information to aid the U.S. Bureau of Reclamation and the Natural Resources Conservation Service in determining where salinity-control work may provide the best results, and to what extent salinity-control work was effective in reducing salinity concentrations and loads in the Colorado River. Previous studies have indicated that salinity concentrations and loads have been decreasing downstream from the Grand Valley Salinity Control Unit, and that the decreases are likely the result of salinity control work in these areas. Several of these reports; however, also document decreasing salinity loads upstream from the Grand Valley Salinity Control Unit. This finding was important because only a small amount of salinity-control work was being done in areas upstream from the Grand Valley Salinity Control Unit at the time the findings were reported (late 1990’s). As a result of those previous findings, the U.S. Bureau of Reclamation entered into a cooperative agreement with the U.S. Geological Survey to investigate salinity trends in selected areas bracketing the Grand Valley Salinity Control Unit and regions upstream from the Grand Valley Salinity Control Unit. The results of the study indicate that salinity loads were decreasing upstream from the Grand Valley Salinity Control Unit from 1986 through 2003, but the rates of decrease have slowed during the last 10 years. The average rate of decrease in salinity load upstream from the Grand Valley Salinity Control Unit was 10,700 tons/year. This accounts for approximately 27 percent of the decrease observed downstream from the Grand Valley Salinity Control Unit. Salinity loads were decreasing at the fastest rate (6,950 tons/year) in Region 4, which drains an area between the Colorado River at Cameo, Colorado (station CAMEO) and Colorado River above Glenwood Springs, Colorado (station GLEN) streamflow-gaging stations. Trends in salinity concentration and streamflow were tested at station CAMEO to determine if salinity concentration, streamflow, or both are controlling salinity loads upstream from the Grand Valley Salinity Control Unit. Trend tests of individual ion concentrations were included as potential indicators of what sources (based on mineral composition) may be controlling trends in the upper Colorado. No significant trend was detected for streamflow from 1986 to 2003 at station CAMEO; however, a significant downward trend was detected for salinity concentration. The trend slope indicates that salinity concentration is decreasing at a median rate of about 3.54 milligrams per liter per year. Five major ions (calcium, magnesium, sodium, sulfate, and chloride) were tested for trends. The results indicate that processes within source areas with rock and soil types (or other unidentified sources) bearing calcium, sodium, and sulfate had the largest effect on the downward trend in salinity load upstream from station CAMEO. Downward trends in salinity load resulting from ground-water sources and/or land-use change were thought to be possible reasons for the observed decreases in salinity loads; however, the cause or causes of the decreasing salinity loads are not fully understood. A reduction in the amount of ground-water percolation from Region 4 (resulting from work done through Federal irrigation system improvement programs as well as privately funded irrigation system improvements) has helped reduce annual salinity load from Region 4 by approximately 7,400 tons. This amount is equal to about 5.9 percent of the total decrease (125,000 tons, or about 6,950 tons/year) estimated to have occurred in Region 4 during water years 1986 through 2003. A geographic information system was used to quantify the change in the amount of irrigated land upstream from the Grand Valley Salinity Control Unit from 1993 through 2000. These data indicated that the amount of irrigated land did not change substantially, thus indicating that the downward trends in salinity load did not result from land-use change.

Colorado↗

USGS2026

Shallow hydrogeologic framework of the Tully Valley mudboil area, Onondaga County, New York

Mudboils have been documented in the Tully Valley in southern Onondaga County, New York, since the late 1890s. Sediment-laden water from the mudboils flows into Onondaga Creek, which empties into Onondaga Lake at Syracuse 15 miles to the north. Turbidity from the mudboils has degraded the water quality of Onondaga Creek despite a series of mitigation efforts that began in the early 1990s. Turbidity mitigation actions presently (2025) being considered include creek relocation and offline sediment settling. In support of these proposed actions during 2021–23, the U.S. Geological Survey, in cooperation with the New York State Department of Environmental Conservation, U.S. Environmental Protection Agency, Onondaga Nation, Onondaga Environmental Institute, and Central New York Regional Planning and Development Board, collected and analyzed geologic, hydrologic, geophysical, and geotechnical data to characterize the shallow hydrogeology along four proposed creek-relocation paths and in the proposed offline settling basin area. The investigation indicated that the four proposed creek-relocation paths, two east of Onondaga Creek and two west of Onondaga Creek, are underlain by sediments including muck, alluvium, mudboil deposits, alluvial-fan sand and gravel, and lacustrine fines. The proposed excavations would penetrate partially to fully saturated conditions: generally, the water table is shallow near the creek and deep on the alluvial fans. The shallowest excavation, about 5 feet below land surface, would be near the creek and primarily in alluvium, and the deepest excavation, as much as 30 feet below land surface, would be in the alluvial-fan deposits. Brackish waters would be penetrated by proposed channel excavations on the eastern side of Onondaga Creek in an area downgradient from a potentially leaking historical salt-exploration borehole and near the main mudboil area. Excavation in these areas likely would provide a continuous source of brackish groundwater to the relocated creek. Proposed channel excavations of muck, soft to very soft lacustrine fines, and mudboil-type sediments in mudboil and suspected mudboil areas would pose an excavation and slope stability challenge and would have the greatest potential to create new mudboils. Proposed channel excavations below the water table on the Rattlesnake Gulf and Rainbow Creek alluvial fans would intercept groundwater and make the constructed streambank susceptible to seepage-induced slope instability. The substantial water-level fluctuation in the sediments of both alluvial fans would aggravate the stability condition. In addition, excavation on the Rattlesnake Gulf alluvial fan would have the potential to affect water-supply springs at the toe of the fan. The proposed offline settling basin area is in the northern part of the Rattlesnake Gulf alluvial fan. Natural and man-made diversions of Rattlesnake Gulf have resulted in saturated conditions in the general area of the proposed basin. The proposed offline settling basin would be excavated in, and berms would be constructed on, alluvial-fan deposits and lacustrine fines. In the proposed basin area, the alluvial deposits overlying the lacustrine fines are less than 10 feet thick. Excavation, berm construction, and loading of the saturated, soft to very soft lacustrine fines may be problematic and require soil strengthening.

New York↗