Stormwater Best Management Practices and Dentistry

By Robert Ketley, Board Director for the Resource Conservation District of Santa Cruz County

Many local businesses and residential developments have vegetated or percolating treatment systems that help clean stormwater runoff. Harnessing the power of biology, chemistry and physics, these systems remove pollutants such as sediments, nutrients, oils and metals. Typically referred to as “best management practices” (BMPs), these wonderful bits of engineered landscaping often blend in with conventional landscaping. Effectively hidden in plain sight, they go about their business while we engage in life, liberty and the pursuit of happiness.

stormwater bmp 01A buildup of sediments and grass is blocking flows into this BMP.Most BMPs are built to handle a typical winter storm event, which in Santa Cruz County means about half an inch of rain along the coast to an inch or so in the mountains. The “rather damp” winter we just enjoyed showed how these systems cope when nature really cranks the faucet open. Some shrugged off the heavy flows, while others didn’t do so well.

Like so many engineered systems, the most common cause of BMP failure is inadequate maintenance. Unfortunately, BMPs don’t come with a “change oil” light to tell you something needs fixing. But there’s no need for despair because the solution is pretty simple - just think like a dentist. Dentists recommended you get your teeth cleaned every six months, and once a year they like to poke and prod to see if anything needs fixing. Use the same approach for BMPs and you won’t go far wrong.

It is best to conduct a cleaning inspection in fall, before the rains start. This will make sure everything is in good shape for when the clouds roll in and dump their wet cargo. By late April you can usually get back out and conduct a spring cleaning/fixing inspection. BMP inspections are a lot like gardening, so get into some grungy clothes and grab a pair of gloves, a rake, shovel and wheelbarrow. Here’s what you do.

Inlets and Outlets

Debris, sediment and weeds are the most common trouble makers. Simply clear out any crud so runoff can flow into or out of the BMP unimpeded.

stormwater bmp 02Sediments washing in from adjacent areas reduce BMP efficiency and increase maintenance costs.Vegetated/Percolation Areas

Runoff should spread evenly across the entire treatment area. Be on the lookout for sediment and/or weeds which can short-circuit or back up flows. For vegetated BMPs, replace dead or diseased plants and apply fresh mulch where necessary. If there is an irrigation system (to help establish plants in the first couple of years) now is the time to check for leaks or damaged/misaligned heads.

Long Term Maintenance

Over time, the BMP will fill up with sediments that get washed off surrounding areas. It’s hard to say how long it will take for a BMP to reach its sediment carrying capacity. BMPs handling runoff from clean, regularly swept areas can take many years to reach capacity. Those serving less well maintained areas, or subject to soils washing off adjacent landscaping can get packed with sediment in as little as one winter. When the sediment layer in the BMP is within an inch or two of the bottom of the outlet it’s time to dig it out. Be warned, removing several inches of hard packed sediment is going to take strong backs and may even need heavy equipment.

If this sort of thing isn’t your cup of tea, fear not. Several local landscape companies have staff who are trained to deal with BMPs. Hire the right company and you’ll sleep soundly through dark and stormy nights.