Stormwater a threat to Lake Tahoe’s declining clarity
All around Lake Tahoe you see them – in parking lots, on the edges of roads, in residents’ yards.
Big piles of snow.
Not white snow, either.
Dirt-, sand- and grease-filled mounds of frozen water.
Where does that water go when it melts?
All that dirty crud?
It all ends up in the crystal clear water of Lake Tahoe.
Fortunately, some of it is treated; unfortunately, not enough.
“If it’s on the street, it’s going straight to a river or the lake,” said Lauri Kemper, chief of the Lake Tahoe unit of the Lahontan Regional Water Quality Control Board. “It’s not the snow that’s a problem. It’s the grime and soot from the roads that’s in the snow.”
Lake Tahoe’s clarity has declined at a rate of about 1 1/2 feet a year for the last 30 years. The decline is largely attributable to the loading of nitrogen and phosphorous into the lake. The combination of the two leads to algal growth.
The Tahoe Research Group of the University of California, Davis has estimated that 37 percent of the phosphorous and 11 percent of the nitrogen loading into Lake Tahoe comes from the particles in runoff.
“When stormwater from roads goes to a drop inlet, it either goes into a tributary or goes into the lake,” said Kevin Hill, hydrologist for the Tahoe Regional Planning Agency. “I think a lot of people think that it goes into the sewer system, and that’s not the case.”
Heavy winters compound the problem. If snow piles up and melts on a somewhat regular basis, provided there are curbs and gutters in the area, officials aren’t as concerned.
However, “In a real heavy winter like we have now, we start running out of places to put it,” Hill said. “Snow plowed over dirt is a bad situation. You remove the top layer of soil and have twice the damage.”
Nature – without urbanization – is able to handle snow and rainfall. The forest floor naturally filters water, so it doesn’t carry sediment particles to the lake. It is when houses, roads and parking lots are introduced that problems develop.
Nature’s process is “short-circuited,” Hill said. Water runoff is one of the key reasons TRPA limits impervious land coverage in the basin. It is also the basis for the agency’s BMPs – Best Management Practices.
BMPs are improvements on each individual property that would result in improving water quality within the Tahoe Basin. They include installing drip-line trenches to catch stormwater running off of roofs, planting native vegetation, paving a dirt driveway and stabilizing eroding slopes.
Based on a 1997 revision to TRPA code, all property – whether business or residential – around Lake Tahoe will need to be upgraded with BMPs eventually, unless it has already been done. All property in the Lake Tahoe watershed is categorized into Priority 1, 2 or 3 areas. Priority 1 areas must be upgraded by October 2000; Priority 2 by October 2006; and Priority 3 by 2011. Most of South Shore is Priority 2.
“On a large scale, if you haven’t installed BMPs, that would be a good measure to take,” Hill said. “Instead of the volumes of water going into streams, it’s being filtered on your property.”
There also are measures that can be taken – and have been taken – by agencies who control street maintenance, such as South Lake Tahoe, the basin’s counties and the California and Nevada departments of transportation.
Around the basin, agencies have installed sand traps in drop inlets, which filter out some sediment particles, Kemper said. They can be inefficient, however, if they are not maintained or if the runoff produces high flows. Agencies, such as the city of South Lake Tahoe, use stormwater vaults, which trap even finer particles and work during periods of strong runoff. Grease and oil separators can be installed in the vaults.
Additionally, retention basins and trenches have been built throughout the basin to act as Mother Nature would if no urbanization was present, filtering out the sediment from runoff.
NDOT uses newscasts from weather stations on the East Shore to give it the most accurate information regarding the snow on the roads. That allows snow removal crews to sand and salt only when absolutely necessary.
Through a nationwide program, agencies are responsible for the runoff from their streets. Lahontan on the California side of the basin and the Nevada Department of Environmental Protection on the other side ensure those agencies make strides to improve their runoff programs.
Lahontan is in the process of reissuing the municipal stormwater permits for Caltrans, South Lake Tahoe and El Dorado and Placer counties. What is identified on the permits ties into programs identified in TRPA’s Environmental Improvement Program.
“They’ve all made a lot of improvements, but we’re not at a pace to achieve what the EIP has set out to do,” Kemper said.
The EIP identifies capital investments that need to be made over the next decade to meet TRPA’s thresholds for water quality, soil conservation, air quality, vegetation, wildlife, fisheries, recreation and scenery. The EIP roughly divides up the $908 million price tag for implementation between federal, state and local governments as well as the private sector.
Hill said at least half of the costs identified in the document are related to water quality and soil conservation work. The costs, however, don’t take into account maintenance of the projects or BMPs.
“There is a lot that has been done. We have made significant progress in the last 10 years, but still there’s a fair amount of (runoff) going straight to the lake or its tributaries,” Hill said. “It’s a hard problem to fix. We’ve made strides, but there are thousands of non-point sources, and it’s hard to treat that many points of runoff. It goes back to the BMPs. Every individual parcel can help.”
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