Mulching and compost turn ordinary urban open space into a stormwater management tool.
Ordinary urban open space functions too when it’s managed well say Virginia Tech researchers. Simple landscape management practices like using mulch and incorporating compost can help repair damage compaction.
Development strips land of vegetation and topsoil. Post-development areas that are not covered with impervious surfaces are often compacted during the construction process–-those soils can’t infiltrate a lot of rainwater and some even shed stormwater like pavement.
Compacted soils are bad for plants too, forcing plant roots to form mainly in the soil’s surface layers. When plant roots penetrate into deeper soil layers, they act as pipes that funnel rainwater deep into the ground.
Compacted soils can be fixed to a degree through good landscape management. A big part of the answer may be in simple solutions like using mulch over bare ground and deeply incorporating compost.
In tests at Virginia Tech, when groundcover cloth was used as a barrier between mulch and soil to handle foot traffic, stormwater runoff increased compared to situations where fabric was not used under the mulch.
During a simulated rain, compacted soils generated runoff with suspended solids at five times the concentration of mulched soils. Over time organic mulches like bark and pine straw can increase organic matter, which improves plant growth too.
Looking beyond mulch, the researchers say that rebuilding urban soils (soil profile rebuilding) to deeper depths (30 to 60 cm) by placing compost deep into the soil profile helps to rebuild organic matter and allows plant roots to penetrate. Rebuilding soil also increases rainwater infiltration.
Can managed open spaces be part of a total stormwater management plan? They ask. Improving soil in open spaces will increase stored carbon, promote root growth and form soil aggregates, all of which will improve stormwater infiltration.
A New Perspective on Opportunities for Stormwater Mitigation through Soil Management in Ordinary Urban Landscapes by Susan Day, Virginia Tech and David Mitchell, Mitchell’s Tree Care & Landscape Consulting in
Watershed Science Bulletin January 2015.
US Composting Council Fact Sheet: Using Compost for Stormwater
An edited version appeared in NewTerrain newsletter August 25, 2015.