Stormwater and Soil

By Jan Allen

What in the heck does compost have to do with stormwater management?

Over the past few decades silt fences and straw bales have been used for stormwater management, often with marginal results.  Increasingly, natural systems using compost and organic matter are recognized as state of the art effective solutions to slowing down stormwater and retaining soil.  As Waste Age points out, “There is an inexpensive and effective method to remediate many contaminated surface waters, soils, air, streams and reservoirs: compost/technology/bioremediation.” -COMPOST: Better, Faster, Cheaper Cleanups

Overlapping Intersections of Soil, Water, Ecology, and Hydrology

In the last ten years a convergence of professionals with new ideas from different disciplines have resulted in discussions about compost, soil quality, hydrology and ecology.  From farms to fish, roads to riverbeds, overlapping interests include: salmon habitat, reduction in polluted roadway runoff, reduction in chemical use on the land, water conservation, soil permeability, native plantings, non-point source pollution prevention and natural treatment systems.  Terms like constructed wetland, biofiltration swale, living roof, compost filter berm, and filtration sox are showing up in best management practices.

This is great news.  The idea of engineering soils using recycled, chemical-free, locally manufactured, indigenous, carbon-neutral materials is an exciting development.  Significant improvements in retention or infiltration of rainfall can be achieved by using simple soil improvement and landscape systems.  The results speak for themselves.

Soil Study Results

A field trial using compost-amended soil and turfgrass system improved retention from 0.4 inches to 1.2 inches for a 1.7-inch rainfall event vs conventional turf design.

Another field demonstration used vegetated biofiltration “strips” to improve runoff retention to 50% by increasing the native soil depth, and to nearly 100% by increasing the depth and percent of organic matter in the soil.

A study on slopes of 15% and 34% grade demonstrated a 3-inch layer of compost performed better than silt fences and performed as well as hydromulch.  The downgradient water did not have metal salts and in some cases leachable metals were reduced.

This challenges all of us to use soils more effectively through the installation of specifically formulated soils that perform to meet hydrologic standards.  Specifically, this means developing “engineered” soils and soil-based management practices that perform as naturally sustainable systems.  It is not necessary to simply accept marginal or damaged soils as a characteristic of the urban or commercial environment.

I began this story asking, “What in the heck does compost have to do with stormwater management?”  The short answer is we are in a “watershed” moment in the world of hydrology.  We at Harvest hope to aid stormwater management efforts by providing compost and organic-based solutions to a landscape near you.

PHOTO SOURCES
Photo 1: http://www.kccwa.org/action.htm
Photo 2: http://www.friendsoftheirishenvironment.net/index.php?do=photos&gId=1
Photo 3: D. Caldwell