Depending on the day and the amount of water flowing, the Carson River carries between 36 and 68 percent more phosphorus than it should, just one of the pollutants identified in the river.
The river has been placed on the list of impaired or threatened water bodies in Nevada and phosphorus levels are being monitored, but no real progress has been made with respect to cleanup, according to Susan Donaldson, water quality education specialist for the University of Nevada Cooperative Extension.
Phosphorus comes from fertilizers and waste, but the primary culprit in Carson Valley is the disturbance of soils, she said.
"Phosphorus binds to soil particles and is released when the soil is disturbed," she said. "We need to stabilized the soil here, but we're not doing a good job of it."
Development and the diversion of water directly into lakes and rivers via storm drains rather than natural filtering processes is at the heart of the problem.
Donaldson was stumping for the use of more natural systems in urban settings for moving stormwater at a Feb. 12 meeting of the Douglas County Planning Commission.
The more traditional structurally engineered systems deliver everything from oil and excess fertilizer to pathogens from pet waste into natural systems like the Carson River.
Direct dumping of stormwater is the most frequently used and expensive method, but it's also the worst thing we could be doing. As the population grows and fields are replaced with cement the problem increases, Donaldson said.
"As communities grow there is an increase in impervious cover. In some places, up to 75 percent of the land is covered by solid surfaces," she said.
Low-impact development, a customized approach to on-site stormwater management using natural systems, is the most important tool against this problem but at this point it's also the least employed, Donaldson said.
For example, clustered development produces smaller lots but leaves more open space, a method that often creates more walkable, family-friendly neighborhoods. Clustering increases the value of neighborhoods and quality of life, a win-win for everyone, Donaldson said.
"The open space absorbs runoff and the developer gets an increase in value with the same number of lots," she said.
Maximizing natural water absorption by using more porous surfaces rather than traditional asphalt or cement, or taking advantage of something as simple as landscaping islands in parking lots, can also decrease infrastructure costs by minimizing the need for expensive storm drains, Donaldson said.
"Parking lots are sized for maximum use, but they're full just a few days out of the year," she said. "If porous surfaces are installed in areas not used as often, like concrete pavers or grass, natural water drainage is increased."
Planning commissioner Jim Madsen said the method wouldn't work on unstable soils.
Conceding that there can be issues, Donald said low-impact development methods are specific to each site, but can be valuable.
Traditional asphalt on Mill Street in Reno has failed due to unstable soils, but Patagonia, a commercial clothing store, has installed permeable concrete pavers in Reno, Donaldson said.
"The (Patagonia) parking lot is just one year old and so far, no problems," she said. "But we're watching it."
Detention basins all over Douglas County are another option that encourages natural filtering of stormwater, but there can be issues with maintenance, and whether the county or homeowners' associations are responsible. The basins can fill with sediment and often don't work, Donaldson said.
She suggests turning them into multi-use areas, like skateboard parks or ball fields, to provide that maintenance.
In other business:
• Commissioner Margaret Pross will serve as chairman for the upcoming year and Commissioner Rick Ross as vice chair. The two won by a 5-2 vote. Commissioners Bob Conner and Mike Olson cast the two dissenting votes.
• Susie Vasquez can be reached at email@example.com or 782-5121, ext. 211.