Stormwater Management Flashcards
(32 cards)
In order to support a shallow permanent pool, Shallow marsh systems need how large of a contributing watershed?
More than 25 acres
Wet ponds should be generally designed to what depth?
4-8 Feet Deep
Pocket wetlands are are typically adapted to serve what size of small sites?
One to Ten acres.
The selection of a particular wetland design usually depends on what three factors?
Available Space,
Contributing Watershed Area, and
Desired Environmental Function
Due to their small size and fluctuating water levels, these wetlands often have low plant diversity and poor wildlife habitat value.
Pocket Wetlands
In many ponds, sediment storage of _______ cubic feet per acre of drainage area can store the sediment delivered over ______ years, after which maintenance for sediment removal would be necessary.
250, 5-10 years.
Water-level rise of less than ______ during frequent water-quality events limits stress on wetland plants.
1 Foot Deep
Total flood storage depth is measured from the ______ invert.
Outlet
Techniques for implementing stream restoration, stabilisation, and enhancement can be thought of in which three categories?
Structural,
Biological, and
a Combination referred to as Soil Bioengineering.
When feasible, urban streams should be buffered with a minimum of _______ undisturbed forest, and an additional ________ of managed vegetated area
8 metres (25 ft), 15-30 metres (50-100 ft)
The process of removing soluble nutrients, metals, and organics by binding ions and molecules to other particles of organic matter or clay. This most commonly occurs in the soil as run-off infiltrates
Absorption
Soluble nutrients can also be removed from storm water by plants in a process called _______. Both toxic heavy metals and essential mineral nutrients are taken up by the roots of the plants and deposited in stems, shoots, or leaves of the plants.
Phytoremediation
Is a chemical activity where a contaminant is changed to a more volatile vapor form. In stormwater management systems, this function transforms complex hydrocarbons, gasoline or other petroleum products in the runoff, into carbon dioxide.
Volatisation
How should sediment be removed?
Through the use of filter strips or sediment traps before it enters an infiltration device.
All surface runoff from paved and unpaved areas is collected and conveyed on the ground, primarily by swales.
The system is discharged or directed to an on or off-site drainageway, stream, or other natural watercourse, an existing street or municipal storm
drainage system, or an on-site retention or sediment pond
Open Drainage System
Surface runoff from paved and unpaved areas is collected at surface inlets and conveyed by underground pipes to an outlet either on or off the site.
Disadvantages include increased cost and complexity
of the system, potential for erosion at the discharge point due to the greater concentration of runoff, reduced filtering of sediment because of increased velocity of the storm water in the pipes, and reduced opportunity for storm water to infiltrate the soil.
Closed Drainage System
Typically, the open system is used in unpaved areas with the intent of providing more opportunity for the storm water to infiltrate the pervious surface, whereas the closed system is used in paved areas. The advantages of this system are reduced construction costs, as compared with a totally closed system, lower potential for soil erosion because of reduced volumes of surface runoff, and lower potential for erosion problems at the outfall because of lower volumes in the pipes.
Combination Drainage System
The required dimensions for grassed swales may be determined analytically or by a variety of published ______ or other design aids. To determine the required dimensions of a swale, the ______ to be handled must be known.
Nomographs, Rate Runoff
Storm water runoff from upslope areas should be prevented from crossing ______ or ______ soils. Diversion measures can be effectively utilised to redirect runoff. Where diversion is not possible, ______ should be used to reduce runoff velocities.
Disturbed or Exposed.
Vegetative Buffer Strips.
An appropriate technique for the repair of small earth slumps that are frequently wet.
Live Staking
Involves the insertion of tamping live, rootable cuttings into the ground. Creates a stabilizing mat that reinforces the soil.
Live Staking
Long bundles of branch cuttings bound together into sausage like structures (Figure 11.4) with the branches and bud ends oriented in the same direction. These bundles are capable of propagation.
Live Fascines
Is somewhat similar to the live fascine system, except that the ______ are oriented primarily perpendicular to the slope. This orientation is more effective in terms of earth reinforcement and mass stability.
Brushlayering
Effective technique for stabilizing slopes by reducing erosion and face sliding.
Placed in shallow trenches parallel to contours for dry slopes, and at an angle to the contours for wet slopes, and are anchored with live and dead stakes.
Live Fascines
