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Wetlands Research
Pittman Wash Pilot Wetlands
The Las Vegas Wash Coordination Committee (LVWCC) initiated the Pittman Wash Pilot Wetlands project to determine whether constructed wetlands could be used to improve the water quality of urban runoff before it enters the Las Vegas Wash.
Urban runoff picks up contaminants, fertilizers, animal waste and other pollutants as it makes its way through the Las Vegas Valley, and it currently accounts for approximately 10 percent of the flows entering the Las Vegas Wash, a percentage that may increase in the future.
The Bureau of Reclamation (BOR),City of Henderson,Clark County Regional Flood Control District, and Southern Nevada Water Authority partnered to initiate the study on behalf of the LVWCC, with construction funded by a BOR grant. In addition to studying impacts on water quality, managers are using the project to evaluate the feasibility of operating constructed wetlands in an urban flood control channel, a setting which presents a variety of challenges and constraints.
The wetlands are located on a 1/3-acre site in Pittman Wash, a flood control channel that drains urban runoff and occasional storm flows from Henderson, NV, to the Las Vegas Wash via Duck Creek. The wetlands are located adjacent to the Arroyo Grande Sports Complex and consist of two small (less than one-tenth of an acre) cells, one with a surface flow regime and the other with a subsurface flow regime. The surface flow cell consists of open water areas that alternate with shallow vegetated beds planted with bulrush, while the subsurface flow cell consists of gravel planted with bulrush. The three species identified through the Demonstration Wetland project were planted in both cells: California bulrush (Schoenoplectus californicus), hardstem bulrush (S. acutus), and Olney’s bulrush (S. americanus). The cells are lined with clay to prevent infiltration by shallow groundwater, which is highly saline and surfaces at various locations throughout Henderson.
The project was first constructed in 2005, but suffered significant damage from several large storm events. In 2006, several modifications were made to help the site better withstand storm flows and the wetlands were restored. Since then, the pilot project has survived several large rain events with relatively minimal damage. Water quality and vegetation monitoring began in 2007. Water quality monitoring is conducted monthly while vegetation monitoring is conducted in the spring and fall.
Preliminary water quality monitoring results show a slight increase in total suspended solids (TSS), total dissolved solids (TDS) and major ions. Metals and nutrient concentrations remain similar in concentrations at the inlet and outlet indicating that the wetlands play a limited role in reducing these parameters. Vegetation monitoring has revealed that Olney bulrush dominates the surface flow cell, having nearly excluded the other two species. Olney bulrush is also the dominant bulrush in the subsurface flow cell, although it only accounts for about a third of the cover. In this cell, landscape weeds like Bermuda grass (Cynadon dactylon) vie with the bulrush for dominance.