For nearly 100 years, scientists have been creating mathematical models for understanding the mechanisms of soil erosion and resulting sediment surface runoff, including a paper in the early 1900s by Albert Einstein, later recognized by the American Society of Civil Engineers to recognize his outstanding achievements in erosion control, sedimentation, and waterway development.
Today, challenges in providing adequate erosion control in the field require a diverse toolbox of solutions. As lands are disturbed, erosion and sediment control professionals are demanding Best Management Practices (BMP) that can be specified, installed, and inspected with confidence. Renewable energy professionals, especially on the operations and maintenance (O&M) side, should take time now to set up proper procedures to prevent problems later. Given the natural settings where renewable energy sites are located, erosion control is essential. Effective erosion controls are not only important to protect a site, but the same techniques prevent water pollution, soil loss, wildlife habitat loss, and property loss.
Protect the site first
Erosion control measures should focus on the site’s attributes. Water always behaves the same way; it seeks its own level. What changes is the topography and elevation in the settling points. As soil is deposited, it diminishes the volume of a drainage route or a retention basin. Therefore, drainage routes and basins must be cleared of accumulated obstructions, dirt, and debris. Flow channels, swales, riprap beds, and culverts must be cleaned out to allow unrestricted water passage. In addition to removing debris, trash, and silt buildup, contractors in O&M should make repairs to drain grates, catch basins, inlets, channels, and roadways to ensure storm water flows freely. Maintain a channel cleaning and maintenance program that addresses vegetation trimming, debris, sediment, and trash in those flood channels.
Blockage in culverts can cause water to flow over roadways and also erode or destroy site access infrastructure. To help prevent this, swales or drainages leading into basins must be intact and capable of carrying storm water at a controlled rate. A breach in a drainage route or flow path negates the design capabilities to move water across the property or into an appropriate catch basin. “Inspect what you expect” by looking at the “story marks” on the property from the last wet weather event.
Good erosion control measures will go a long way when it comes to preventing or controlling erosion on both wind and solar energy projects. Hydroseeding is a quick, cost efficient way to apply seeds, mulch, and fertilizer to recently disturbed soils. The value of hydroseed can be seen in both erosion control and dust mitigation. It’s also an effective revegetation strategy. Selecting the right contractor is always important and ensuring they have trained applicators who have sprayed on renewable energy projects. Seed mix, mulch rate, fertilizer, application uniformity, overspray mitigation, and other factors must be considered. Selecting the right seed mix for a projects’ climate and soil content and working with an unbiased consultant to help determine the appropriate seed is also important. The seed mix can change the price per acre by hundreds of dollars. With projects ranging from 20 acres to 2,000 acres, this cost can be significant.
Weed control is a big land management issue, especially after El Nino drenched most of the nation this year. Weeds are expected to be at an all-time high, just as fire season kicks in. It could be a good idea to budget a little more than usual for this year’s O&M.
One of the biggest weed challenges is contending with tumbleweeds, or Russian Thistle. In the Antelope Valley last year, more than 2,000 tons of tumbleweeds were removed from both solar and wind projects. Tumbleweeds can cause serious problems when they get caught up in racking systems, cable trays, pylons, and inverters. In order to prevent these problems, it’s best to be proactive. Each weed can produce up to 200,000 seeds and they contain flammable oils. Mow them while they’re still green and physically remove them from the site. Also plan and permit a chemical weed abatement program.
Key points to consider when using hydroseeding:
Dry vegetation is an extreme hazard, especially around potential ignition sources. Owners and operators may expect more visits from fire departments this year thanks to El Nino, so it’s important to be in compliance. Most municipalities or county fire departments have vegetation management regulations to remove or mow to a prescribed height before the start of the fire season. Inspections are conducted throughout the dry season, and the property must be maintained in order to remain in compliance. Even if a property owner abates their property early in the season, there is potential for re-growth.
For all power facilities managing vegetation around equipment where an ignition source could occur is another BMP. Around power transformers and inverters, vegetation should be removed in a radius of not less than 15’. Clearing this radius will help prevent a fire from starting if the component has a major failure causing sparks. Inside substations, fenced parameters should be managed to bare ground or rock. In fields, low growing vegetation is often encouraged as a means of mitigating dust, mowing to a height 4” is a BMP to minimize the fire hazard while allowing low ground cover to provide dust prevention.
Most fire requirements ask for a defensible space of 500’ for the site, but codes vary by region. Clearing around power poles, transformer pads, and junction boxes is essential. A 10’ radius around power poles will help prevent a fire from starting if there is any arching due to a failed component. Trees and large brush should be cleared at least eight’ below a power line.
Most roads in high risk fire areas are left 20’ wide after a project has been constructed, allowing for access, and acting as a fire break. Using parameter roads and fence lines as a fire break is a site’s best defense for the spread of fire whether the source is internal or external. Keeping the ground cover and fence line maintained may require seasonal inspections and services to remove accumulated windblown vegetation.
Given all of the potential devastating effects from erosion, O&M professionals should take every necessary step they can to minimize damage and protect their projects. The past decade of droughts and catastrophic wildfires have left parched landscapes ill prepared, so site assessments and maintenance practices are particularly critical.
Harvey Stephens is the vice president of operations at World Wind & Solar. Harvey is a true solar industry pioneer with 30 dedicated years of utility scale solar experience starting in 1986 with construction and operation and maintenance of the first solar thermal projects in the US. Harvey is a co-owner of WWS, an energy service provider in the renewable energy sector. Providing complete services including land management, reflectivity maintenance and panel cleaning, predictive and preventative maintenance, and full service electrical capabilities from new construction through operations and maintenance, the company also provides staffing and QA/QC services for both the wind and solar industries. WWS successfully services all major turbine and panel manufacturers at scores of renewable energy facilities throughout the United States from New Hampshire to Hawaii.
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