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Las Vegas, NV, United States

Hester G.A.,Southern Nevada Water Authority
43rd International Erosion Control Association Annual Conference 2012 | Year: 2012

Over the last several decades a number of the urban areas of the southwestern United States have experienced explosive population growth. With increasing populations and expanding urban sprawl, often come increased wastewater discharges, higher dry weather urban runoff and larger storm water discharges. Naturally formed receiving streams are now tasked with conveying increased urbangenerated volumes of flow. Often these outfall streams become de-stabilized with resulting increases in the rates of channel bed and bank erosion, higher volumes of sediment discharge, degradation in water quality and loss of valuable riparian lands. One of the largest single stream restoration programs currently underway in the western U.S. and an example of one community's successful efforts to combat stream zone erosion, to restore wetland and riparian habitat, to improve the quality of water discharging into Lake Mead, and to develop recreational opportunities, is Southern Nevada's $270 million dollar effort to stabilize and restore the non-federally owned portion of the 20 kilometer (12.5 mile) long outfall stream known as the Lower Las Vegas Wash. This paper describes how this massive effort, which is now nearing completion, was formulated and has become successful through many years of multi-agency cooperation, comprehensive, adaptive planning, and environmental sensitivity.

Hester G.A.,Southern Nevada Water Authority
43rd International Erosion Control Association Annual Conference 2012 | Year: 2012

The use of rock riprap for grade control structure design has become a popular method of stream channel stabilization and restoration. Understanding the hydraulics and forces involved with discharges over riprap gradient control structures is paramount to the long term success of most stream channel restoration projects. Considerable research has been previously devoted to developing rock-sizing methodologies and characterizing hydraulic stresses on rock riprap. However, stream restoration specialists are often confused as to the most appropriate methodologies to apply during the planning process and in many cases are left uncertain of the realistic capability of riprap gradient control facilities to sustain varying flow conditions over the long term. To give stream channel restoration professionals more confidence in channel stability design and application, the Southern Nevada Water Authority enlisted the assistance of Colorado State University's Engineering Research Center to conduct a wide range of large scale physical hydraulic modeling of rock riprap grade control structures to aid in determining the most appropriate design methodologies to apply for long term success. 1:6 Froude-scale rock riprap grade control models, containing varying D50 riprap sizes, were developed and subjected to a wide range of discharges during the study. This paper summarizes the results of the study and is supplemented with field observations of actual installations under high discharge conditions.

Saltonstall K.,Smithsonian Tropical Research Institute | Lambert A.M.,University of California at Santa Barbara | Rice N.,Southern Nevada Water Authority
Biological Invasions | Year: 2016

While hybridization between Native and Introduced Phragmites australis has not been documented across much of North America, it poses an ongoing threat to Native P. australis across its range. This is especially true for native populations in the biologically rich, but sparsely distributed wetlands of the southwest United States, which are among the most imperiled systems in North America. We identified multiple Hybrid P. australis stands in the Las Vegas Wash watershed, NV, a key regional link to the Colorado River basin. Rapid urbanization in this watershed has caused striking changes in water and nutrient inputs and the distribution of wetland habitats has also changed, with urban wetlands expanding but an overall reduction in wetland habitats regionally. Native P. australis has likely been present in the Wash wetland community in low abundance for thousands of years, but today Hybrid and Native plants dominate the shoreline along much of the Wash. In contrast, Introduced P. australis is rare, suggesting that opportunities for novel hybridization events remain uncommon. Hybrid crosses derived from both the native and introduced maternal lineages are widespread, although the conditions that precluded their establishment are unknown and we did not find evidence for backcrossing. Spread of Hybrid plants is likely associated with flooding events as well as restoration activities, including revegetation efforts and construction for erosion control, that have redistributed sediments containing P. australis rhizomes. Downstream escape of Hybrid plants to Lake Mead and wetlands throughout the lower Colorado River basin is of management concern as these Hybrids appear vigorous and could spread rapidly. © 2016 Springer International Publishing Switzerland (outside the USA)

Adhikari A.R.,Desert Research Institute | Acharya K.,Desert Research Institute | Shanahan S.A.,Southern Nevada Water Authority | Zhou X.,Southern Nevada Water Authority
Environmental Monitoring and Assessment | Year: 2011

Increased water use associated with rapid growth in the Las Vegas Valley has inadvertently led to the creation of unique wetland systems in Southern Nevada with an abundance of biological diversity. Constructed and naturally created wetlands in the Las Vegas Valley watershed were studied to characterize and understand their potential role for improving ecosystem services (i.e.; water purification). Nutrient and metal removal was assessed at four sites including a natural urban runoff wetland, a constructed urban runoff wetland, a constructed wastewater wetland, and a natural urban runoff/wastewater wetland. Plant nutrient uptake was dependent on ambient nutrient concentrations in water and sediments of specific wetlands, irrespective of the type of plants present. Phosphorus was mostly concentrated in below-ground plant parts whereas nitrogen was concentrated in above-ground parts. As for metalloids, bulrushes were more efficient than cattails at taking up arsenic and selenium. Averaging all the wetland sites and plant species, total nitrogen, phosphorus, arsenic and selenium removal was 924.2, 61.5, 0.30, and 0.38 kg/ha/year, respectively. Our findings suggest that natural and created wetland systems can improve water quality in the Las Vegas Valley watershed for some common pollutants, however, other measures are still needed to improve water quality below regulatory thresholds. © 2010 Springer Science+Business Media B.V.

Ryan R.,Southern Nevada Water Authority | Zhou X.,Southern Nevada Water Authority
Lake and Reservoir Management | Year: 2010

The Las Vegas Wash (Wash) is the primary drainage channel for the Las Vegas Valley. Flows from the tributaries are a major source of contaminants of particular concern to the Wash, mainly total dissolved solids (TDS) and selenium (Se). Treated wastewater effluent discharged to the Wash currently provides enough dilution to lower the TDS and to maintain selenium concentrations below the current 5μg/L aquatic life criteria recommended by the Unites States Environmental Protection Agency (EPA; USEPA 1987); however, the Systems Conveyance Operations Program (SCOP) was intended to take most of this treated effluent through a pipeline directly into the Boulder Basin of Lake Mead. While construction of the pipeline may have had many water quality benefits for the Las Vegas Valley and Lake Mead, the dilution benefit to the Wash will be significantly reduced, primarily affecting TDS and Se concentrations in the Wash. The Wash enters Lake Mead at Las Vegas Bay, home to the endangered razorback sucker. The concern is the increased concentration of TDS and Se to the Las Vegas Bay, which potentially would impact the razorback sucker. Using data collected by the Southern Nevada Water Authority's (SNWA) environmental monitoring and management water quality team, projections have been made for expected TDS and Se concentrations post completion of the SCOP. These projections show 2 options for managing TDS and Se concentrations on the Wash: dilution and/or treatment of the tributaries. Discharging 2.08 × 10 5 m 3/d to the Wash provides the necessary dilution to lower Se to the target concentration of 5 μg/L but will still leave TDS levels higher than desired. Treating one or more of the major tributaries will bring both Se and TDS concentrations within targeted levels. © 2010 Copyright Taylor and Francis Group, LLC.

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