Construction and grading activities such as earth-moving and excavating can greatly increase the potential for soil erosion. Especially during wet and windy weather, the likelihood of eroded soil particles (sediments) being delivered into streams and the lake is extremely high. For these reasons, the Lake Tahoe Basin, like many communities, attempts to greatly reduce the potential of these negative impacts reaching the lake during construction activities.
Since Tahoe has what is called a Mediterranean climate, with wet winters and dry summers, one strategy to control negative impacts from construction is to limit grading and excavation during the wet winter months. For this reason, Tahoe’s building season is limited to May 1 to October 15. Outside that time period, no activities disturbing more than 3 cubic yards of soil can be legally permitted or performed.
Another strategy to limit construction-induced sedimentation is use of temporary best management practices (BMPs) during construction of new structures or landscapes. BMPS are techniques designed to reduce water pollution from land management activities.
Just as all home and business owners are required to install permanent BMPs, all excavators, pavers, builders, and other contractors must install temporary BMPs prior to starting new projects. These BMPs can be as simple as fencing off natural areas on a property that can be left totally undisturbed during construction. These natural areas should be as large as possible, and are to remain off limits to driving, parking, and materials storage. The bonus at the end of construction is that property owners will have a slice of undisturbed natural habitat adjacent to their home. Not only does this provide beauty and opportunities for wildlife viewing, it also requires no maintenance, other than annual pruning and cleanup of debris for defensible space purposes.
This year, the Tahoe building season began with over a week of snowy, stormy weather, adding to the unusually large accumulation of snow during April. Fortunately, since nearly all Tahoe contractors are receiving training about proper installation of temporary BMPs, the potential for damage from early season wet weather construction was diminished. Many contractors simply delayed early bulldozing projects. Others, who needed to excavate on relatively flat properties, carefully installed filter fences and fiber logs on the downslope sides of their projects. These devices caught and detained muddy runoff, so that it deposited sediment on-site, instead of draining to a roadside ditch or stream and then into the lake.
All BMPs at Lake Tahoe, whether temporary or permanent, must be designed to infiltrate the runoff from a “20-year, 1-hour storm” into the soil on the property. This equates to receiving approximately 1 inch of rainfall during an hour. Sometimes, because we generally have such clear, rain-free summers, builders are surprised by an intense thunderstorm that drops an inch of rain in an hour on a June, July or August afternoon. For this reason, contractors and their workers must frequently inspect all BMPs to make sure they will work effectively throughout the year.
Like most lake restoration efforts comprising the Lake Tahoe Environmental Improvement Program (EIP), temporary and permanent BMPs are being improved year-by-year. For example, a few years back, contractors routinely placed straw bales around grading projects during construction. Now, because such straw bales have been found to be a source of noxious weed seeds into the basin, they have been largely replaced by a new line of weed-free erosion control logs, fences, and fabrics. As new entrepreneurs enter the BMPs field, whether as designers or installers, the rising supply of erosion-control products is expected to bring down costs and improve the lake we all love.
The Lake Tahoe Report 016
Air Date: 2003.05.20
Video Segment: Building Season Begins
Interviewees: Matt Graham (TRPA) and Birgit Widegren (TRPA)