FLOOD03407

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Stormwater Management in the United States - A Study of Intsitutionl Problems, Solutions and Impacts
• Date: 9/1/1980
• Prepared By: Office of Water Research and Technology
• Floodplain - Doc Type: Educational/Technical/Reference Information

on ground surfaces, on paved surfaces such as parking lots and outdoor shopping
malls, on rooftops of buildings having level roofs, and in underground pipes, tun-
nels and reservoirs. Many local governments and other stormwater control agencies
require that land developers include such on-site storage of stormwater in the con-
struction of surface drainage systems. Other things that a stormwater management
agency may require a land developer to do "on-site" to control runoff flows and
prevent damages are: allow roof and pavement drainage to flow over grass and other
vegetation prior to entry into the drainage system; install suitable landscaping
and ground cover, and grade the ground surfaces to maximize infiltration; use ab-
sorbent paving materials where feasible (e.g., porous asphalt); avoid disturbing
or blocking natural floodplains, floodways, rivers, creeks, gulches or swales;
control soil erosion during development by observing prudent grading practices and
restoring the ground cover promptly in open areas; and, most important, avoid con-
structing buildings or other vulnerable structures in flood hazard areas.

In-Stream Control of Runoff. Generally, where runoff flows have entered
either a storm sewer system or natural drainageways (creeks, rivers, lakes), it is
complicated and expensive to control the flows. Various measures used in natural
streams include: stream channel widening, straightening, dredging and cleaning;
bank stabilization; construction of either on-stream or off-stream reservoirs; and
reconstructing or replacing bridges and culverts to provide a sufficiently large
waterway opening to accomodate peak flows. In storm sewer systems, regular clean-
ing of pipes and catch basins is important to assure the proper operation of the
system and to keep the system clear of concentrations of pollutants which would
otherwise be flushed into natural water bodies downstream. In combined sewer sys-
tems, measures are required to minimize the frequency and quantities of sewage over-
flows and treatment plant by-passes. Correction of such problems requires major
construction in the form of storage facilities, enlarged sewers, reduction of ground-
water infiltration, and additional treatment plant capacity. Some urban areas have
begun sewer-separation projects so that they can handle stormwater and sanitary
wastes in two different systems.

Using Runoff Beneficially. Many opportunities are available in almost all
urban areas to make beneficial use of stormwater. This usually involves capturing
the excess runoff for either temporary or long-term storage in ponds, reservoirs,
channels, pipes or tanks. When ponds are planned for stormwaterdetention, features
may be incorporated into the design to permit various multiple-purpose uses. Often,
the additional construction costs involved are not prohibitive. Sometimes, local
park districts or local governments are willing to share the construction costs of
such stormwater detention ponds when recreational facilities are provided. These
may include provisions for boating, fishing, ice skating and swimming. Also, the
areas surrounding a detention pond can be developed for passive recreation and serve
as a aesthetically pleasing buffer zone. In some arid and semi-arid urban and sub-
urban areas, stormwater is a valuable resource for use in irrigation of grass and
other vegetation in parks, parkways and on nearby farms. This entails temporary
storage of excess runoff in ponds and open channels, prior to its use. In other
urban areas, excess runoff is injected or infiltrated into the earth to replenish
groundwater supplies. It appears probable that urban stormwater runoff, someday,
will be used as a secondary water source when water supplies in many urban areas
become inadequate for the ever-increasing populations. Uses for such secondary
water supplies may include: cooling water in cooling systems of large buildings and
power generating plants, manufacture of products, general cleaning, etc,

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