Low Impact Design (LID) refers to managing stormwater runoff at the source (on-site) using green infrastructure techniques. Keeping water on-site reduces the need for much larger and more costly management systems. It also helps prevent flooding by reducing the amount of water that enters surface waterways during flash flood events. Conventional stormwater management uses a pipe-and-pond technique which replaces natural systems with concrete, pipes, ponds, and extensive infrastructure. These systems channelize the water and increase its velocity; thereby greatly increasing the risk of erosion. The goal of LID is to replace these pipes and ponds with soft engineering practices that: filter, infiltrate, store, and evaporate the run-off on-site. Incorporating LID early in the planning and design of a project has proven to be much more cost-effective while also providing a community benefit and a much better-looking project. Each of these major components of LID is discussed below.
FILTER
Filtering happens early in the management of stormwater runoff within the systems used to convey water to storage and infiltration facilities. In modern
engineering, these conveyance systems are typically pipes and concrete channels. However, LID replaces these pipes and concrete with vegetation. Some
types of these systems include vegetated filter strips, bioswales, rain gardens, infiltration trenches and basins, and green roofs.
Below are examples of how some of these systems work.
INFILTRATE
After runoff has been filtered it is then conveyed to an infiltration system. It is these systems that prevent flooding by depositing water underground
during a rain event rather than overflowing creeks, streams, and rivers. These systems decrease the impact and cost of developing a site by requiring
less stormwater storage infrastructure on-site or downstream. It also helps replenish our groundwater supply rather than let water flow downstream
where it will eventually end up in the ocean. Infiltration techniques include pervious surface materials, infiltration basins, rain gardens, bioswales,
and infiltration trenches.
Each LID component can be used individually to manage stormwater runoff, but the design of these components in a system of infiltration trenches, rain gardens, bioswales, and basins can serve larger-scale developments.
STORE
Detention and retention ponds are the most common ways to manage runoff on large development sites. They are effective yet can be repetitive and sometimes boring. A few more unique ways to store
stormwater include underground detention, wet vaults, and rainwater harvesting. These systems can be useful for commercial sites where surface area
is limited but are not as efficient or cost-effective as detention/retention ponds are on large sites.
EVAPORATE
Any water that was not able to infiltrate back into the ground due to soil saturation or a severe rain event will hopefully return to the atmosphere
by transpiration through vegetation or by direct evaporation. This would put water back into the natural cycle rather than continue downstream, unused,
until it reaches the ocean or to increase the risk of flooding.
A FINAL WORD
Some of the techniques described above are better for small scale residential lot use while others are used for entire community stormwater systems.
Each has a different purpose, and all can be beneficial. However, the main principles of LID can be applied in any situation: filter, infiltrate, store,
evaporate.
7gen Planning
Austin
9050 N. Capital of Texas Highway,
Building 3, Suite 390,
Austin, Texas 78759
Phone: 512-646-3454
Houston
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3rd Floor
Houston, Texas 77042
Phone: 713-343-0394
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