The Stormwater Stars Workshop Series
Restore the Watershed. Build Community.



This web page is intended to give you an overview of the landscape practices that you will learn in much greater detail when you attend the Stormwater Stars Workshops. The Stormwater Stars program is provided with financial support by West Multnomah Soil & Water Conservation District. The Stormwater Stars program is provided in cooperation with West Multnomah Soil & Water Conservation District, Oregon Department of Environmental Quality, Southwest Watershed Resource Center, Portland Bureau of Environmental Services, Green Girl Land Development Solutions LLC and Stamberger Outreach Consulting.

Runoff Reduction Overview (Rationale)

Reducing runoff with a strong emphasis on infiltrating runoff is a top priority for many jurisdictions; however, there are many lower risk practices that landowners can implement to improve the watershed.

There are a number of creative solutions that take a two-pronged approach to runoff (i.e. high volume flows draining from a particular area and directed to a particular area) and rainfall (i.e. low volume rain that falls on the facility itself before becoming concentrated):

1. Limit the volume of runoff actively directed into the ground, instead using evaporation and uptake by plants.
2. In landscape areas, restore the historic hydrologic function by encouraging evaporation and/or infiltration of rainfall.

The practices (aka BMPs or best management practices) you choose must reflect the opportunities and constraints of the site, the stakeholders, and budget, and will result

in unique combinations and configurations. Considering Southwest Portland's tight clay soils – a resident once took some from his yard, and successfully fired a piece of pottery from it – runoff from semi-permeable areas like lawns and walking paths are just as important to manage as hard, impervious areas like the roof, gravel driveway, and concrete walkways.

The more effective practices are sometimes the lowest cost practices:

Runoff Reduction Approach
Estimated Runoff Reduction
Manages Through
Restored Soils then making the area:
Rainfall on Landscapes Evaporation & Infiltration
Rainfall on Landscapes Evaporation & Infiltration
  Shrub Garden
Rainfall on Landscapes Evaporation & Infiltration
($1.11/sf, $1.21/sf)
Depaving (Removing unneeded bits of pavement) then making the area:
Rainfall on Landscapes Evaporation & Infiltration
Rainfall on Landscapes Evaporation & Infiltration
  Shrub Garden
Rainfall on Landscapes Evaporation & Infiltration
Native Tree & Shrub Landscapes
80% - 100%
Rainfall on Landscapes Evaporation & Infiltration
Container Gardens or Raised Beds Over Hard Surfaces
40 – 50%
Rainfall on Hard/Impervious Surfaces Evaporation
Porous Walkways
Rainfall on Hard/Impervious Surfaces Evaporation & Infiltration

(Wood Chip $0.67/sf
Gravel $1.97/sf)

Rainfall on Hard/Impervious Surfaces Evaporation

Site Planning

Locating stormwater practices is made easier with our Site Analysis Checklist. This list is a place to log general and specific site considerations, areas, and asks important stakeholder questions related to water quality & plant establishment, like "Are there dogs present?" Also included are some recommendations, such "Call 811 before you dig.

Download the Stormwater Stars Site Analysis Checklist [pdf]

Restored Soil

Soil is the foundation of healthy watersheds, cleansing water slowly through its pores, seeping out to feed our waterways long after the rain has stopped. Soil also provides the structure and nutrition for plants to grow, which are key to providing us with clean and plentiful water. When we pave over or compact soil and take up pore space in the watershed with basements, runoff increases and water quality degrades.

Just ripping soil hasn’t been found to be successful at restoring long-term permeability, but soils amended with compost can reduce runoff by 50% to 80%, depending on whether the final treatment is lawn, meadows, or shrubs, respectively.

To restore the permeability and quality of tight clay soils, here's what to do:
1. Till or loosen the soils with a shovel to a depth of 12". (Remove the lawn first, if you're going to install a meadow or perennial or food garden.)
2. Apply US Composting Council Seal of Testing Assured compost and Permamatrix to the surface (see table below for best depth).
3. Till the compost or shovel into a mixture with the existing soils to a depth of 8".
4. Cover the soil with 3" of US Composting Council Seal of Testing Assured to prevent erosion, make weeding easier, and to feed the plants over time.
5. Plant the area with lawn, meadow, or perennial or food garden.

Permamatrix is a product that has mycorrhyzae (beneficial mushroom roots), microorganisms, and other great ingredients to reduce water demand during plant establishment. The mycorrhyzae work in a symbiotic relationship with the plant roots, each delivering what the other needs to thrive.

Compost can be around $115/yard if you have it delivered but only $20 to $30/yard if you pick it up. Permamatrix is $39/50 lb bag that covers about 500 square feet. They now have a 6 lb bag that also covers 500 square feet.

IN AREAS OF SPOTTY ESTABLISHED PLANTS: Soil permeability is said to be restored, albeit more slowly, by simply adding compost tea and mycorrhyzae treatments to an area, without tilling it. Cover this area with US Composting Council Seal of Testing Assured Compost if it's not too steep or use some other erosion control methods.

Download a fact sheet for this practice

For this area:
Apply this much compost in Step 2:
Why use different depths?
So you don't have a lawn that's wavy/irregular, but instead is flat


If shorter grasses are used & a wavy/irregular yard will be noticeable
If taller grasses are used or a wavy/irregular yard is not a concern
Because you won't see the surface under the shrubs and 3" of compost reduces more runoff than 1.75"
  • Never add sand alone to clay soils as this causes them to cement up!
  • Always amend a whole garden area, not just the hole you’re putting your plant into.

It’s likely that there are many little paved areas throughout the watershed that no one needs or uses but collectively are impacting water quality downstream. Tearing out pavement and replacing it with landscape area, also known as depaving, is an effective means of restoring your watershed. What you replace it with (lawn, meadow, shrubs, and/or trees) determines how effective depaving is.

Many people believe that gravel drains well, but in fact, gravel roads and driveways tend to generate almost as much runoff as a conventional asphalt road and would benefit from depaving, too. There is quite a bit of preparation that can go into depaving and it may involve removing rock below a surface. For more information on depaving, visit the website of the folks who thought up this idea, Depave (

Download a fact sheet on this practice.

Container Gardens

Container gardens are a great way to reduce runoff when placed over a small patch of impervious area that you’re really not using, but don’t want to remove quite yet (aka depaving). They can function like ecoroofs (aka green roofs) on the ground, evaporating 50% of our rainfall on an average year for every square foot of impervious area they sit over.

We mixed US Composting Council Seal of Testing Assured compost and Permamatrix into our native clay soils, and filled our pots with this. To reduce watering, we planted them with more native plants that will be hardy in hot, sunny places since a container surrounded by pavement will get extra hot, and we added GeoHumus, which holds water and releases it later to reduce irrigation needs.

Tip: Don’t use potting soil, as this is likely to have fertilizers, which are pollutants. Remember, 50% of the time, there’ll still be runoff and pollutants in your containers will be very efficiently carried via your impervious area to waterways or, if they drain to a pervious area, groundwater may be polluted.

Download a fact sheet on this practice

Porous Walkways & Patios

Porous walkways are porous surfaces that allow rain to pass through them and provide a desirable walking surface, which includes boardwalks & decks, mulch, gravel, and pavers. In order to be beneficial for reducing runoff, porous walkways must be porous from their surface, all the way through to the native soils below. There is a common misconception that all pavers are porous (or permeable); however, this isn't true. Often, when a paver is installed, the soil below is heavily compacted and the pavers are placed tightly together to create a barrier to rainwater. With a properly installed porous walkway, the soil is not compacted and the pavers are placed just a little bit apart, to allow rainfall to pass through the cracks. Porous walkways can have a variety of looks, from manufactured (left) to more natural and organic (right). We might even use salvaged materials or poured-in-place concrete to lower the cost.

Download a fact sheet on this practice

Tree Planting

Trees are the foundation of a healthy watershed and a healthy community. In addition to cleaning the air, holding soil, reducing runoff from landscape and hardscape areas, trees on the street or in your yard can increase your property value by 3 to 15% and provide a host of other social and economic benefits.

Some handy and not widely known statistics: When trees are planted to shade

  • Asphalt pavement, it improves the longevity of the pavement.
  • An air conditioning unit or heat pump, the energy efficiency of that unit is increased by 10%.
  • A house, homeowners can save 20% on their energy bills, on average.

One of the most common mistakes in planting trees is putting them in an area without enough soil. Provide trees with adequate soil volume for tree growth and stability. The tree should be able to access 3 feet of soil, which is about as deep as the roots of most trees will grow. With this depth available, small trees will need about 140 square feet of area, medium trees about 240 square feet, and large trees about 340 square feet.

The benefits of new trees are often small when first planted and accrue over time. New trees can cost as little as $3 when bought as bare root (i.e. not in a pot) at a native plant sale or nursery or $75 to $100 as a larger "instant gratification" tree.

Detailed info on choosing trees, pruning, plant health care, planting and a Tree Owner's Manual are available from Trees Are Good.

The left and center trees were 2 feet tall when they were planted, one year after the tree on the right, which was 5 feet when it went in. Four years later, the smaller trees have grown to the height of the larger tree that was planted a year earlier. This is an example of how smaller trees become established and grow faster than larger trees.  
Supporting Info: Native Landscapes

Native plant species have many benefits:

  • Native plants attract native pollinators that increase yield from edibles plants.
  • Native plants are essential to healthy watersheds. They provide unique ecosystem services and products in our region that other non-natives may not provide. They evolved over geologic time periods with other plants and animals in our watersheds and support the insects, that feed the birds, that spread the seeds, that grow the forests, that give us clean water, that save us money.
  • Native plants are generally easier to establish, and require less water and fertilizers. 
  • Lower possibility of invasive behavior than non-natives. Non-natives may provide the services above, but they may also become invasive, and there's often no way to know which path a plant will take until it has been introduced into a watershed. Some non-natives took 80 years to become invasive after overplanting (i.e. kudzu planted on the East coast for erosion control); some spread quickly from just a few specimens (i.e. scotch broom originated from three specimens introduced in the late 1800's and now dominates the Pacific NW landscape).

To put the right plant in the right place, determine all the combinations of moisture (wet, moist, and dry) and light (sun, part sun, shade) and pick plants that are well suited to these areas. A number of natives might volunteer (i.e. blew in or were brought by birds as seed), and you may choose to leave them alone or transplant them somewhere else in the fall or early spring. If you can tolerate the wild look featured in the photo at the top of this page, you provide a lot more habitat and have to do a lot less weeding, since many of our weeds aren’t shade tolerant. Unless a plant has become diseased, don’t clean out dead material underneath the plants; this is nature’s mulch that saves you money and protects plant health by limiting disturbance.

Trees & shrubs are a great way to reduce runoff by intercepting rainfall and will also evaporate more than lawn areas as a result of their more robust root systems. Meadows are great for pollinators.

Visit Green Girl's Native Plants Portal for info on choosing plants for pollinators, erosion control and more!

Additional Resources

Where to Find Materials

Porous Walkways - Rock
Read the fact sheets for information on specifications, but here's a friendly reminder: Don't forget to ask for "washed and clean" rock.

Porous Walkways - Mulch

Restored Soil - Soil Amendments

Erosion Prevention & Sediment Control

Past Project Sites -- Photo Stream

Before: Compacted lawn in full sun is incapable of supporting even a healthy cover of grass. A compacted gravel walkway (not shown) creates a muddy condition in the lower left hand corner.

One Year After: Porous gravel walkway (in lower left corner) solves the drainage problems in this corner. A porous mulch walkway makes weeding without compacting the garden easy and attractive. The native plant garden is growing in. The container over the hardscape/sidewalk was added by the homeowner later.

More Trainings & Programs for Residents and Landowners in Portland

Backyard Habitat Certification (Audobon Society)

Urban Watershed Mentors (West Multnomah Soil & Water Conservation District)

Bring Back the Pollinators (Xerxes Society)

Disclaimer: Green Girl Land Development Solutions LLC provides information for educational and outreach purposes only, to enhance the sustainability of sites. Unless adopted by the appropriate registered professional under contract, information provided is not for construction.

Updated 15 Nov 2016