Stormwater runoff is a major cause of water pollution

Stormwater runoff is a major cause of water pollution in urban areas. When rain falls on our
roofs, streets, and parking lots in cities and their suburbs, the water cannot soak into the
ground as it should. Stormwater drains through gutters, storm sewers, and other engineered
collection systems and is discharged into nearby water bodies. The stormwater runoff carries
trash, bacteria, heavy metals, and other pollutants from the urban landscape. Higher flows
resulting from heavy rains also can cause erosion and flooding in urban streams, damaging
habitat, property, and infrastructure.
Fig: storm sewer systems
Storm water planning
1. Drainage is regional and does not respect boundaries between jurisdictions or
properties.
2. Storm drainage is a subsystem of the urban water system.

3. Every urban area has two drainage systems (minor and major).
4. Runoff routing is a space allocation problem.
5. Storm water problems should not be transferred from one place to another.
6. Urban drainage should be multi-purpose and multi-means.
7. Storm water systems should consider natural drainage system functions.
8. After development, storm water flows should remain at predevelopment conditions
and pollutant loadings should be reduced.
9. Storm water systems should be designed beginning at the outlet.
10. Storm water systems should receive regular maintenance.
11.
Stormwater management is required to mitigate the effects of urbanization on the hydrologic
cycle including increased runoff, and decreased infiltration, of rain and snowmelt. Without
proper stormwater management, reduced baseflow, degradation of water quality, and
increased flooding and erosion can lead to reduced diversity of aquatic life, fewer
opportunities for human uses of water resources, and loss of property and human life.
Watershed planning integrates environmental and land use planning. Criteria for the
protection of water quantity, water quality, habitat, and biota are established to help achieve
the goals set for the watershed. Strategies to manage human activities within the watershed
are developed to meet protection criteria. A stormwater management strategy may include
protection of natural areas, design of communities to reduce stormwater generation, and
pollution prevention programs, as well as the stormwater management practices which are the
focus of this technical manual.
A combination of lot level, conveyance, and end-of-pipe stormwater management practices
are usually required to meet the multiple objectives of stormwater management: maintaining
the hydrologic cycle, protection of water quality, and preventing increased erosion and
flooding. Lot level and conveyance controls may be classified as storage or infiltration

controls. Storage controls are designed to detain stormwater. Although the volume of runoff
does not decrease, the risk of flooding is reduced because all the stormwater runoff does not
arrive at the stream at the same time. Infiltration controls are necessary for soil moisture
replenishment and groundwater recharge. They can achieve water quality enhancement but
are ideally suited for infiltration of relatively clean stormwater including rooftop and
foundation drainage. Pre-treatment of road drainage is necessary to prevent clogging of a
system and to protect groundwater quality.