The chances of topsoil
loss dramatically rise if a landscape receives sheeting water from nearby features. Driveways, roadways, sidewalks, and parking
lots are often designed to sheet their runoff to the landscape. If this is the case on your property, divert that runoff away
from the landscape and towards the storm drain system.
below are the costs, effectiveness, longevity and maintenance of some the common emergency diversion devices: bales, check
dams, drainage ditches, dry stacked walls and sandbags.
Description: Oat, barley,
wheat, and rice straw bales used to depower and divert runoff and sediment. They are used along roads, the base of slopes,
and around the perimeter of structures,
Bales are inexpensive and quickly placed and staked.
Effectiveness: These devices are good at diverting and depowering low to medium flows
Bales are a short-tem remedy and are typically pulled up and composted after the threat of rain has passed; they become a
fire hazard and a habitat for all kinds of unwanted animals if left in place.
Maintenance: The devices are very low maintenance.
Description: Check dams are staked boards running
mostly perpendicular to the flow of runoff. These small walls are used to both divert and slow runoff. The boards are generally
4 ft long, 9 in wide and ½ in thick. Two ft stakes made from #3 rebar are used to keep the boards in place.
Costs: Check dams are
inexpensive and quickly built.
Staked devices are effective for low to moderate flows of runoff only.
Longevity: Staked boards rarely last longer than 3 years; less if
they manage regular flows of runoff. Maintenance: These devices will eventually fail by
either getting pushed over or having its uphill side fill with debris and sediment. Keep the uphill side clean to reduce pressure
and increase longevity.
are quickly dug to transport water away from a vulnerable area. They are generally 6 in to 1.5 ft deep and 1.5 ft to 3 ft
dug with no material costs.
Earthen features are only suitable for low to moderate flows of runoff; anything more leads to rapid deterioration.
Longevity: If the diversion
ditch is not lined with river rock or planted, then it will degrade within 2 years.
Maintenance: Diversion ditches are short-term solutions
are require maintenance to retain its shape during the rains. Generally, diversion ditches are turned into concrete ditches,
dry creeks or swales. Refer to the next chapter.
Dry stacked walls are made from rock, broken concrete, bricks, and even roof tiles, and used to divert, direct and depower
runoff. They are usually short walls running mostly perpendicular to a slope or water path. Gravity, opposed to concrete,
holds them together.
Stacking walls is labor intense, but the materials are generally inexpensive.
Effectiveness: These walls can be built to withstand low to high
flows of runoff. They are not as effective as sandbags, but they are longer lasting and more aesthetically appealing.
Longevity: Stacked walls
can be long lasting if built with care.
Two types of problems occur with these walls. First, dirt and debris will collect on the wall’s upslope side, reducing
its water holding and slowing capacity, while increasing pressure on the structure. Remove this accumulation every 2 to 4
years. Second, the downward side of the wall will erode, eventually undermining it. Every 2 to 3 years pull the soil back
up to the wall and either plant to stabilize or compact it. Refer to the section on Terracing in Chapter 11 for greater detail.
Description: Mostly impermeable small
walls made from bags filled with sand, aggregate or soil. Bags are laid and compacted in a running bond pattern.
Costs: Material costs are inexpensive,
but labor costs can be high.
Very effective in the short-term for low to high flows of runoff.
Longevity: These small walls are good for 2 years, but the bag’s hemp
or plastic weave deteriorates rapidly after that.Maintenance: Sandbags are a short-term
solution and within 2 years of installation they need to be removed and a permanent solution installed.