Hillside Stabilization Tips
Waterfront lots in Seaview Terrace may deal with unique challenges and concerns regarding residential hillside stability, especially in areas with steep slopes or close proximity to Colvos Passage.
In an effort to assist SVT homeowners with options that address bank stability challenges while staying compliant with Seaview Terrace Protective Covenants, see the following information.
*All information below is provided to help educate homeowners on State and County regulations and guidance. The Seaview Terrace Homeowners Association is not liable for any damage to property within it’s membership due to hillside vegetation/drainage maintenance, or lack therof.
Source: Washington Department of Fish & Wildlife, published February 2016
Vegetation (p. 18 from Your Marine Waterfront):
Vegetation is one of the easiest and most affordable techniques to install and maintain. It protects slopes by stabilizing soils and is good for fish and wildlife. Native flora is well adapted to our climate.
Use good quality native plants (see page 37) and those with deep roots like shrubs and trees. A planting plan should consider the bank exposure and steepness, soil type, hydrology, intensity of development, and an assessment of existing vegetation
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- FRAME VIEWS: Arranging plants to accommodate and complement special views may help prevent removal of vegetation in the future when plants mature or a property is sold.
- ENHANCE VEGETATION: Avoid removing, topping, and excessive pruning of existing trees, as their roots stabilize the soil. Keep existing native vegetation and plant new trees and shrubs to mimic a pre-development environment.
- LEAVE LEANING AND FALLEN TREES: Leave leaning trees in-place unless an arborist determines they are hazardous. Allowing trees to fall naturally and the logs to decompose on-site provides no-cost erosion protection and important habitat for fish and wildlife.
- CONSERVE AND RESTORE SOIL: Conserving topsoils during construction helps to retain the organic matter within existing soils. Some soil may need to be amended to better support plants.
- ACCOMMODATE DRAINAGE: Placing plants and soils appropriately is important to ensure they fit into the overall drainage plan for rainwater and septic systems. This may include planting water-loving plants in lined swales and rain gardens.
- USE EROSION CONTROL PRACTICES: Applying erosion control techniques (e.g., laying straw over soil) on recently laid or disturbed soil will help keep topsoil in place while plants establish and grow.
Drainage (p. 20 from Your Marine Waterfront):
Drainage is often paired with vegetation. Piping water over a steep slope (left) with a diffuser tee outfall (middle) can promote stable bluffs. Rain gardens (right) lined with a waterproof barrier can filter run-off as it flows into the drainage system.
Design drainage projects to reduce the volume of water that might: 1) erode slopes at the surface or 2) cause landslides (see diagrams on page 14). Specific practices will depend on site conditions like the property’s geology, pattern of water movement, and erosion risks.
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- ENHANCE VEGETATION: Keeping existing vegetation and adding new plants, especially native vegetation, will help absorb water and stabilize the soil and slope.
- MINIMIZE IMPERVIOUS SURFACES: Reducing driveway lengths and widths, and building up rather than out, will reduce surface water flow and allow rainwater to be absorbed by plants.
- USE RAIN BARRELS: Collecting rainwater and reintroducing it over a large area that doesn’t affect slope stability will reduce the amount of water saturating the bluff during heavy rains.
- CLEAN RAINWATER RUNOFF: Directing rainwater flows to lined rain gardens will prevent water from seeping deeper underground and toward the bluff. Rain gardens also filter runoff. Combine this with an underground drainage system.
- INSTALL A DRAINAGE SYSTEM: Installing a drainage system that carries water to the beach or to a professionally identified safe place (e.g., stormwater storage area) will reduce landslide and surface erosion risks.
- SLOW WATER AT OUTFALL: The outfall is the last point on the piped system where the runoff discharges to the beach. Placing a diffuser tee or other water-slowing device at a proper height will help prevent erosion of the beach.
Selecting Native Plants (p. 37 from Your Marine Waterfront):
**Please be cognizant of property views of ALL members when selecting plant type, height and location for hillside stabilization/landscaping projects.**
Washington state has many native plant species that are well-adapted to the unique conditions of the marine shoreline environment. Existing native vegetation should be preserved wherever possible, as these plants provide habitat for local wildlife and help stabilize soil. To find plants best-suited to the unique conditions of your site, work with a local professional and/or native plant nursery.
TREES*
| Common Name | Exposure Needs | Moisture Needs | Max Height (ft) | Growing Ease |
| Big-leaf maple | sun-shade | dry – moist | 100 | High |
| Douglas fir | sun – partial shade | dry – moist | 250 | Medium |
| Grand fir | sun – shade | dry – moist | 250 | Medium |
| Hookers willow | sun | moist – wet | 20 | High |
| Madrone | sun – partial shade | dry | 90 | Low |
| Pacific crabapple | sun – partial shade | moist – wet | 40 | Medium |
| Red alder | sun – partial shade | dry – wet | 120 | High |
| Shore pine | sun – partial shade | dry – wet | 50 | HIgh |
| Sitka spruce | sun – partial shade | moist – wet | 200 | Medium |
| Vine maple | partial shade – shade | dry – moist | 25 | High |
| Western hemlock | partial shade – shade | moist – wet | 225 | Medium |
| Western redcedar | partial shade – shade | moist – wet | 200 | Medium |
*Please consider ALL SVT member property views when planting trees.
SHRUBS
| Common Name | Exposure Needs | Moisture Needs | Max Height (ft) | Growing Ease |
| Bald hip rose | sun – shade | dry – wet | 4 | High |
| Beaked hazelnut | sun – shade | dry – moist | 20 | Medium |
| Dwarf Oregon grape | partial shade – shade | dry – moist | 3 | Medium |
| Evergreen huckleberry | partial shade – shade | dry – moist | 6 | Medium |
| Indian plum; Osoberry | partial shade – shade | dry – moist | 15 | Medium |
| Nootka rose | sun – partial shade | dry – moist | 10 | HIgh |
| Oceanspray | sun – shade | dry – moist | 15 | High |
| Salal | partial shade – shade | dry – moist | 5 | Medium |
| Salmonberry | sun – shade | moist – wet | 10 | High |
| Serviceberry; Juneberry | sun – shade | dry – moist | 20 | High |
| Snowberry | sun – shade | dry – moist | 5 | High |
| Sweet gale | sun – partial shade | sun – partial shade | 4.5 | Medium |
| Sword fern | partial shade – shade | dry – moist | 3 | High |
| Thimbleberry | sun – shade | dry = moist | 8 | Medium |
PERENNIAL / GRASS-LIKE
| Common Name | Exposure Needs | Moisture Needs | Max Height (ft) | Growing Ease |
| Common spikerush | full sun | wet | 3 | Medium |
| Douglas aster | sun – partial shade | dry – moist | 3 | High |
| Dunegrass | sun | wet | 3 | High |
| Fleshy jaumea | sun – partial shade | wet | 0.5 | High |
| Golden-eyed grass | sun – partial shade | moist – wet | 1.5 | Medium |
| Large-leaved lupine | sun – partial shade | moist – dry | 5 | High |
| Lyngbye’s sedge | sun – partial shade | wet | 3 | Medium |
| Pickleweed | sun | moist – wet | 1 | High |
| Puget Sound gumweed | sun | dry – moist | 3 | Medium |
| Seacoast bulrush | full sun | wet | 2 | Low |
| Sea-watch | sun – partial shade | moist – wet | 5 | Medium |
| Slough sedge | sun – partial shade | moist – wet | 3 | High |
| Tufted hairgrass | sun – partial shade | dry – wet | 3 | High |
| Western columbine | sun – partial shade | moist | 2 | Medium |
| Yarrow | sun – partial shade | dry – moist | 0.5 | High |
GROUNDCOVERS
| Common Name | Exposure Needs | Moisture Needs | Max Height (ft) | Growing Ease |
| Beach/Coastal Strawberry | sun – partial shade | dry | 1 | High |
| Broad-leaved stonecrop | sun | dry | 0.5 | High |
| Graceful cinquefoil | sun | moist | 2 | Medium |
| Henderson’s checker mallow | sun | moist – wet | 5 | Medium |
| Kinnikinnick | sun – partial shade | dry | 1 | Medium |
| Silverweed | sun – partial shade | moist – wet | 1.5 | High |
| Thrift; Sea pink | sun | dry – moist | 1 | High |