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Who will maintain the creek long-term?

As from January 2013 Sonoma County Water Agency will maintain the Cotati Creek Critters’ restoration site under its Stream Maintenance Program.

For further information see: http://www.scwa.ca.gov/stream-maintenance-program/ and
Community Voice:_SCWA Will Continue Cotati Creek Critters Work In Laguna (pdf)

The Laguna de Santa Rosa Foundation www.lagunadesantarosa.org will maintain the second site from Gravenstein Way to Commerce Blvd., under contract to Sonoma County Water Agency.


The information below was written in 2007 in response to questions from local residents. It is left here as historical and reference information.

The creek/flood control channels in Cotati for years have been cleared of most trees and shrubs. How will the plantings affect flood control?

For decades creeks and flood control channels were typically stripped of all trees and shrubs that were thought to interfere with flood conveyance and channel maintenance. This creates several problems that have been recognized and this has caused a major shift in maintenance practices, not just here, but throughout California.

1) With an abundance of water, fine sediments and full sun, the creek channel becomes ideal for vigorous plant growth. Channels become overgrown with fast-growing vegetation including invasive non-native Himalaya blackberry. Native cattails and other emergent plants also thrive in these conditions. This in-channel vegetation can reach 8’ in height in a single season and is difficult to manage. This growth traps more sediment and trash, filling in the channel and lowering flood capacity.

2) Water in the channel exposed to the sun heats up. Warm water contains more bacteria and less dissolved oxygen than cool water. Native aquatic life, including steelhead and salmon, are adapted to cool water and perish in warmer temperatures. While we do not have steelhead and salmon in Cotati, water leaving here supports migrating fish downstream. Water from Cotati flows 14 miles to the Russian River, and is used for everything from drinking water wells to recreational fishing and swimming.

3) Tree roots provide excellent bank stabilization and prevent soil erosion and bank failures, which is a problem in some areas in Cotati. It has been calculated that the Laguna de Santa Rosa as a whole has accumulated 1 1/2’ of sediment over about the last half-century, decreasing flood control capacity significantly. By keeping sediment out of the system we help maintain its ability to store flood water that flows out of our community.

Our plantings will provide a shady canopy that will suppress excessive growth of vegetation in the channel and keep water cooler, with less bacteria and more dissolved oxygen. The stems or trunks of the trees and shrubs provide less resistance to water flow (known in hydrology as “roughness”) than a blackberry- or cattail-clogged channel. The real constrictions to flood conveyance in Cotati and elsewhere are undersized culverts under bridges and roadways. If you look at the bridges at Benson Lane or East Cotati Ave. this becomes quite apparent. Not only is the opening only a portion of the cross-sectional area of the creek, but there is a bridge support right in the center of the creek, further impeding flow.

We plant trees and shrubs alternately, on approximately 10’ spacing. Most trees end up being about 20’ apart, which is not overly crowded for riparian (streamside) trees. Our goal is 80% survival, and we would expect some mortality over time. Trees close to the water are planted at the “toe,” which is just up on the bank from the active channel. Alders naturally grow here and are recognized for their bank-stabilizing roots. Red willows and dogwood are planted here as well. These trees will provide the shade right over the active channel, suppressing unwanted growth and ultimately reducing maintenance. Combined with the trees higher on the bank it will provide a dense shady canopy that will also provide a welcome respite for people to enjoy on hot summer days.

Statewide and within the Laguna de Santa Rosa watershed only 5-10% of historic riparian forest and plant communities remain. Our planting project will begin the process of restoring ecological functions to this flood control channel that will have the added benefits of providing habitat and conductivity, improving air and water quality, moderating summer temperatures, buffering noise, increasing groundwater infiltration, sequestering carbon and providing a natural green space for the enjoyment of Cotati residents.

Will all these plants create a fire hazard?

The non-native grasses that currently dominate the creek grow up to 6’, go to seed and die off in the summer before being mowed. These grasses are fire-prone and we are actively managing them with repeated mowing and weedwhacking to prevent them from going to seed and to reduce their vigor. Repeated mowing over several years, combined with the growing tree canopy will ultimately suppress the weedy, fire-prone, non-native understory. The native riparian plant community that will replace it is one of the few that is not fire-prone, or worse (especially for places like southern California chaparral), fire-dependent.

We have grant funding for a project beginning in 2008 to plant native grasses, sedges, rushes and forbs under the canopy of our small growing trees where we have suppressed weeds with mulch. These native perennial plants will stay green year-round and have vegetative growth of about 1-2’ tall. As the weedy growth is suppressed we expect the native plants to be able to compete and hopefully reestablish dominance. Tree roots primarily provide the bulk protection of banks with thick, strong, woody roots. While non-native annual grasses have shallow roots which can be torn away leaving exposed banks, native grasses and sedges have thin, dense, fibrous roots that can penetrate 10’ or more and hold soil particles. Deep, perennial roots of the entire riparian plant community create an effect through “transpiration pull” which results in the rehydration of the soil surrounding the stream corridor by drawing up moisture from deep below the surface. This will result in higher humidity in the air and higher water content of the plant material, which will result in a lower fire hazard than currently exists.

Isn’t it unsafe to have stakes next to a bike path?

When we plant, we mulch the plants with cardboard and rice straw to suppress weeds around the plants and maintain moisture in the soil. We use wooden stakes for three reasons:

• to mark the location of plants so they are easy to spot for maintenance and mowing
• to keep the cardboard and straw mulch in place
• we use a large stake on the upstream side of the plant to help protect the plant from debris which can get washed down the creek and can otherwise smother or break the plant. The stakes are reclaimed from landscapers that discard them.

As avid cyclists ourselves, we take bike safety seriously because we deal with it all the time as riders. The stakes are not in the path. Anyone straying off the path may encounter other potential hazards such as rocks, trees, clumps of grass, holes, concrete chunks, storm debris and stormwater outfalls. The safest thing is to stay on the path. In response to public concerns a risk assessment officer from SCWA inspected the site and determined that she could see no significant safety risks. The officer noted that the top of the stakes is the same area in square inches as the mushroom caps that OSHA recommends to prevent impalement hazards.

What’s your position on dog walking along the Laguna?

We can’t think of a better place to walk your dog in Cotati than along the Laguna bike path. We have politely informed some dog walkers of the two existing city ordinances that require that all dogs be on a leash, and owners clean up after their dogs. We support these ordinances for several reasons:

1) Off-leash dogs can be intimidating, if not dangerous to other path users and other dogs on a leash. Any bike rider can tell you stories about being chased by off-leash dogs. We have heard from seniors and parents with young children that they don’t feel comfortable on the path with off-leash dogs. Dogs being walked on a leash may react defensively/aggressively when approached by an unrestrained dog.

2) Dogs running loose through the creek may chase or disturb wildlife and damage plantings. Dogs can also be hurt by hidden hazards like stormdrain outfalls.

3) Dogs running through the water in the creek have later become ill, likely due to pollutants or pathogens in the creek. Dog waste is a known contributor to bacteria in waterways that impacts human and ecological health.

Cotati has a dog park intended especially for dogs to run around off-leash and to socialize. The dog park is budgeted to have the drainage improved, making it useable during rainy months.

How will the increasing tree cover impact mosquitoes?

With the arrival of West Nile Virus the management of mosquitoes has taken on a greater sense of urgency. The office for the Marin/Sonoma Mosquito & Vector Control District, on the west side of Cotati, actively surveys the waterways of Cotati and treats for mosquitoes using “mosquito fish” or Bti larvicide.

A mosquito larva develops just below the water’s surface and breathes air through small tubes like a snorkel. Any significant disturbance to the water surface, like wind ripple or flowing current, disrupts the breathing tubes and kills the larva. Mosquito larvae are usually found in small pockets of stagnant, protected water. In larger bodies of water, dense vegetation below the surface can protect larvae from predation by fish, amphibians and insects, as with the invasive Ludwigia downstream in the Laguna.

A clear running active channel with little emergent vegetation will naturally discourage mosquitoes by allowing predation to occur because of minimal plant cover and the exposure of the water surface to wind and flow ripples. The suppression of emergent plants in the active channel by a tree canopy will facilitate active management of mosquitoes, yet reestablishment of natural biological and physical control mechanisms may diminish or eliminate the need for regular management.

What about the safety of the public using the trail?

Some people have expressed concern about the potential for undesirable characters to “hang out” near the creek. This can be true in areas where paths are not well used by the public. The answer is to have “eyes on the creek” and we believe that by caring for the creeks, picking up trash, and having the trails well used and appreciated by the public, less desirable characters won’t be as likely to hang around. There were concerns about this by neighbors when the bike path was first installed north of East Cotati Avenue several years ago. People who used to sleep out in the bushes prior to the bike path being constructed actually left the area afterwards and the path is now well used and enjoyed by people out walking, running, and bicycling on a regular basis.

Another indication that caring for an area increases respect for it, is that where the Cotati Creek Critters have been working regularly, there is now far less trash than there used to be, not only because we are clearing it up but because less of it is being discarded there in the first place.

We would encourage path users to program the local Cotati police number into their cell or home phones to report illegal behavior. By making the Laguna path a more pleasant place to be, and with a future connection across E. Cotati, regular use of the path will only increase in the future.

Jenny Blaker, Outreach Coordinator

Wade Belew, Stewardship Coordinator

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Updated 2013 by Lucy Kenyon