Minimize
Storm Runoff
SMMC 7.10.050
By diverting stormwater from impervious areas such as roofs and paths,
and by reusing it whenever possible, urban runoff can be greatly reduced.
This can be achieved by directing rain gutters to landscaped areas,
drywells and infiltration basins where water can seep into the ground.
Placing landscaped
areas directly below eaves allows roof runoff to percolate into the
sub-soil. Plants should be sturdy enough and provide a subsurface matrix
of roots to tolerate heavy sheet flow runoff and periodic saturation.
Landscaped infiltration
basins for storm-water retention should have flow directed toward them
with curbs, berm, or similar structures, and slightly concave to retain
surface water until it infiltrates.
Drywells (also known
as “French drains”) are particularly valuable for small sites,
since they can supplement limited infiltration areas. These consist
of a hole filled with open-graded aggregate, such as #2 or 3 stone,
wrapped on the top and sides with filter fabric. Drywells should be
at least 15 ft. from building foundations at the bottom of sloped landscaped
areas, covered with at least 1 ft. of soil.
Manufactured sediment
traps are available that intercept runoff from drainage areas, and slowly
release it while trapping sediments.
Cautions
- A soils engineer
should be consulted for soil suitability, and to size drywells.
