This information rich section explores traditional and innovatiove concepts to control and manage Storm Water and Erosion. Site specific options are necessary to control the movement of silt and sediment particles in the sensitive areas on Cape Cod. Because the air is also considered a fluid, air and water move particles in similar patterns and can be managed with similar techniques.
Erosion control systems should always be designed for zero discharge.
Construction activity removes the natural vegetation which normally slows and infiltrates rainwater. Uncontrolled erosion depletes resources by transporting topsoil and subsoil down slope, creating gullies and smothering down slope and wetland resources. Properly installed erosion control systems will perform in compliance with Conservation Commission and Endangered Species permitting regulations.
Preventing and controlling erosion is a major plus for anyone building Green.
Smart Growth Techniques, Low Impact Design and Green Building systems all agree that erosion can easily be prevented with a few simple guidelines: First, design your site to prevent erosion. Reduce your construction envelope to minimize de-vegetation. Second, design with the natural flow of hydrology. Don’t create problems from excess sheet flow discharge. Third, design different systems for different needs. Make your choices based on slope and contributing flow. Several basic tools are used to work with erosion control systems: heavy scissors, sharp knife, heavy hand maul, heavy duty stapler, tape measure, lawn edger tool.
Several basic components make up the majority of erosion control systems:
Here are a few examples of the materials, systems, and techniques that we use.
Straw, made up of grassy stems, usually second cutting after the seed heads have been harvested for hay. We use straw because hay would introduce non-indigenous seeds. Straw us used to trap eroded sediment.
Jute netting, also inappropriately called “erosion cloth”. We use jute as a cover for sloped bare ground and to construct bio logs.
Sand fence, also called snow fencing. The slats control beach erosion by slowing down wind.
Silt fence, a semi-permeable filter fabric which traps fine silt but allows water to seep through. 36 and 24 inch silt fencing is available. We only recommend 24 inch fencing for erosion control systems. The fencing comes with stapled stakes every 10-12 feet. We staple an extra stake in the middle of each section to create fabric tension which improves performance.
A significant percentage of 36 inch silt fencing fails to perform in Outer Cape weather. It also requires stakes every 2 ‘ to last through the winter. We no longer use or recommend 36″ silt fencing. Are people who still use this expecting 36″ of rain?
The fastest way to install silt fencing is with a lawn edger. Digging trenches to install fabric is counterproductive, expensive and creates additional soil erosion next to the area you should be protecting.
Fabric is stretched tight and stapled to additional stakes. Putting staples in vertically works best.
Poorly staked silt fencing should never be depended on as a “stand alone” system for controlling downslope erosion.
Each straw bale is broken up into “flakes” which get spread out along 30 feet of jute netting to build bio logs.
Longer sections of bio log/silt fence systems should always incorporate animal bypasses. These should overlap in an upslope direction, so the by pass can still function as erosion control.
Bio logs can be used on side slopes or gentle slopes. This side slope bio log/silt fence system is shown after successfully performing during a surprise, fifty year storm water event. This site also incorporates straw bales downslope.
Steep slopes create serious erosion potential. We used double staked straw bales on top of this slope next to a planned demolition and excavation site. When slopes become eroded, double staked bales need to be placed at the bottom of the slope, where wetlands usually begin.
Straw bale erosion control systems are only effective if they have continuous contact with each other.
“Decorative” erosion control systems are clearly nonperforming, unprofessional and indicate a lack of Conservation Commission supervision.
Erosion control systems that obviously fail to meet performance standards are unprofessional and point out a lack of understanding of the site conditions and erosion control alternatives.
We use 24″ sand fencing in an area like this. The slats can be driven into place with a rubber mallet.
Silt heavy loam should never be stored upslope from wetland resource areas without silt fencing and sediment barrier erosion control system in place.
Failures in silt control systems are most often generated by improper installation of silt fencing, using oversize silt fencing that is 36″ instead of 24″ tall and ignoring the need for regular inspections. This site represents all three problems.
Sand fencing prevents wind generated sand erosion by controlling wind speed. Fencing placement should be three to six feet apart for best performance. Fencing also generates sand deposition because when wind is slowed down, it drops the sand it is carrying. Fencing slats can be individually driven into the sand instead of using additional stakes.
Redirecting foot traffic from a crumbling edge of this coastal bank may prevent unnecessary erosion.
Coconut husk fiber rolls prevent coastal erosion by absorbing wave energy. For more information regarding site specific erosion control options, contact Gordon at firstname.lastname@example.org
We design and evaluate storm water management options based on sustainability,Â low profile, low maintenance andÂ gravity driven systems. Most of these systems are also low cost. Check out our new Storm Water Management page under Educational Initiatives on our Home Page. This section is being frequently updated this fall.
Storm Water Performance Standards
Safe Harbor designs storm water systems with zero discharge performance standards. On site mitigation provides ground water recharge for sheet flow and point source discharge. Massachusetts Smart Growth initiatives advocate for the protection of our water resources.
Safe Harbor advocates for minimal de-vegetation and grade alterations on construction sites to minimize potential storm water generation and discharge. This also significantly reduces erosion control and re-vegetation costs. We also strongly advocate use of sustainable, indigenous vegetation systems. Native stem-leaf-root systems naturally reduce runoff velocity and remove pollutants, sediments and silt. These systems also contribute to habitat values.
These are some of the options we choose from.
1.Â Â Rain Garden
2.Â Â Rain Barrel irrigation
3.Â Â Cistern Storage
4.Â Â Filter Strips
5.Â Â Vegetated Swale
6.Â Â Stone Swale
7.Â Â In Ground Dispersal System
8.Â Â Drip Lines
9.Â Â Dry Wells
Unmanaged storm water generated by impervious paving contributes animal, vehicle and road waste directly into our coastal wetlands. Workable management systems are available for municipal and residential use. Storm water should be infiltrated into the ground water table to meet performance standards for wetland areas. Some towns on the Cape still have work to do in this area.
Plowed snow is storm water, complete with road and vehicle waste. It is important to get it recharged to ground water and not dump in into our harbors. Snow should be directed to designated swale areas for storage, away from harbors.
De-vegetation on Slopes Means Potentially Expensive Erosion
We prefer working on job sites from the beginning of construction, but that doesnâ€™t always happen. We would have re-designed this 100 foot driveway which was dumping runoff down slope. During a storm water event, the driveway generated thousands of pounds of water. The acceleration of gravity multiplied the weight of water. We use straw bales for steep slope emergencies like this one because a salt marsh is at the very bottom of this slope. We also try to re direct upslope sheet flow.
The angle of the camera makes it difficult to read the slope but we have created inverted terraces to infiltrate runoff. We have also applied our bio-engineered re-vegetation system, using indigenous compost, mulch and pine needle/oak leaf litter. This matches adjacent, indigenous soil profiles. Jute netting, partially visible here, contributes to stabilization by holding materials in place pending development of root/stem systems. Straw bales are left until indigenous vegetation naturally controls slope runoff. The driveway angles have also been modified.
Same slope, second year growing season. We look for indigenous survivability between 65-75%.