Storm Drain

Storm Drain

A system designed to drain excess rainwater and groundwater from paved streets, parking lots, sidewalks, and roofs.

Storm Water

Water that enters the storm drain system, including rainfall runoff, snowmelt runoff, and surface runoff.

Rainfall Runoff

Water from rainfall that flows over the land surface and may enter ditches, streams, and storm drain systems.

Run-Off

The portion of precipitation that makes its way toward streams and other bodies of water.

Surface Run-Off

The portion of precipitation that flows over the surface of the ground.

Sub-Surface Run-Off

The portion of precipitation that moves below the ground surface.

Basic Problems of Storm Water

Subsurface water and surface water runoff may constitute excess water that is detrimental to plant life.

Effect of Surface Run-Off

Surface runoff causes erosion and may be retained in surface depressions.

Structural Damage from Excess Water

Excessive surface and subsurface water can cause structural damage to foundations, concrete slabs, and other building structures.

Storm Drain Function

It is designed to drain excess rainwater and groundwater from paved streets, parking lots, sidewalks, and roofs.

Storm Drain Sources

Storm drains are fed by street gutters on most motorways, freeways, and other busy roads, as well as in towns that experience heavy rainfall, flooding, and coastal areas that experience regular storms.

Best Management Practice (BMP)

Measures developed to control, store, and/or treat stormwater runoff from developed areas for the purpose of reducing flooding or removing pollutants while maintaining or enhancing environmental quality.

Open System

A drainage system that uses swales, open channels, canals, etc.

Closed System

A drainage system that uses catch basins, drain inlets, area drains, trench drains, curb inlets, manholes, cleanouts, headwalls, end walls, etc.

Advantages of Closed System

More collection points allow surface runoff to be collected more quickly; it also provides aesthetic purposes.

Disadvantages of Closed System

Higher cost; more complex system maintenance; filtering of sediments is not as effective; and water is not absorbed by the ground.

Collection

Catch basins, drain inlets, area drains, and trench drains.

Conduction

Underground pipes that convey collected water.

CDP

Concrete drain pipe.

Combination System

A drainage system that provides separate drainage of paved and unpaved areas.

Advantages of Combination System

It results in low soil erosion and reduces construction costs.

Disposal

The disposal of stormwater may be through on-site or off-site disposal.

Field Disposal

Field disposal using tiles, also called field tiles.

Perforated Pipes

Also called tiles, these pipes allow water to infiltrate into the surrounding soil.

Natural Disposal

Disposal into natural bodies of water such as streams, lakes, and oceans.

Engineered Disposal

Disposal through municipal sewers, floodways, detention basins, channels, etc.

CHANNELS AND SWALES

Channels and Swales

Designed to convey peak discharges of runoff.

Swale Cross-Section

For ease of construction and hydraulic performance, swales are typically designed with trapezoidal cross-sections.

Swale

The term "swale" is common in urban drainage.

Swale and Road-Edge Grassed Channel

The distinction between a swale and a road-edge grassed channel is not always made.

TYPES OF CHANNELS AND SWALES

Grass Channels

Drainage channels designed to convey runoff without erosion or overtopping.

Grass Channel Flow Depth

Flow depth should not exceed 100 mm (4 in).

Grass Channel Longitudinal Slope

Longitudinal slopes should not exceed 4% or be less than 1%.

Dry Swales

Distinguished from a simple drainage/grassed channel by the addition of carefully selected, highly permeable soil, usually sandy loam, check dams, and an underdrain system.

Purpose of Dry Swale Design Features

These design features ensure that infiltration of stormwater will not depend only on the infiltration rate of the existing natural soils.

Wet Swales

Distinguished from a simple drainage/grassed channel by design features that maintain a saturated condition in the soils at the bottom of the swale.

Goal of Wet Swale

The goal is to create an elongated wetland treatment system that treats stormwater through physical and biological action.

FILTER STRIPS

Filter Strip

A type of buffer strip consisting of an area of vegetation, generally narrow and long, that slows the rate of runoff, allowing sediments, organic matter, and other pollutants conveyed by the water to be removed by settling out.

Benefits of Filter Strips

Filter strips reduce erosion and the accompanying stream pollution and can serve as a best management practice.

BIORETENTION

Bioretention

A technique whereby parking lot islands, planting strips, and swales are used to collect and filter storm runoff.

DETENTION AND RETENTION SYSTEMS

Dry Detention Pond

Typically designed to drain within 72 hours after a rainstorm, with the discharge rate controlled at or below the pre-development peak discharge.

Dry Detention Pond Function

After a rainstorm, dry detention ponds slowly release collected water into culverts. The water releases slowly through a pipe installed at the lowest area of the basin.

Dry Detention Pond Discharge

The water may then flow to other land areas or into a nearby water source, such as a river or stream.

Wet Detention Pond

Designed to have a permanent pool of water with additional volume above the water surface for handling runoff pulses.

Wet Detention Pond Cost

Wet detention ponds may cost more to build and maintain than dry ponds.

Wet Detention Pond Benefits

They tend to be more aesthetically pleasing, conducive to wildlife habitation, and, in some cases, may be more effective.

Wet Detention Pond Appearance

These ponds tend to resemble standard man-made lakes and are surrounded by natural vegetation.

Retention Basin

A best management practice intended to mitigate stormwater runoff.

Retention Basin Function

Water is detained in the basin while pollutants are treated by natural processes, and water exits the basin slowly over time or during the next storm.

Retention Basin Water Quality

Processes such as mechanical settling of suspended sediments and biological processing of nutrients contribute to improved water quality.

Retention Pond

A pond designed to hold a specific amount of water indefinitely.

Retention Pond Overflow

A retention pond usually has drainage leading to another location when the water level rises above the pond capacity while still maintaining a certain capacity.

Detention Pond

A low-lying area designed to temporarily hold a set amount of water while slowly draining to another location.

Detention Pond Purpose

Detention ponds are primarily used for flood control when large amounts of rain could cause flash flooding if not managed properly.

INFILTRATION BASIN

Infiltration Basin

A pond designed to "leak" into the underlying soil.

Infiltration Basin Failure

These facilities have a high failure rate and short life if not protected by an upstream sedimentation basin.

Infiltration Basin Design

Infiltration basins must be specifically designed to infiltrate.

BASIN LANDSCAPING

Basin Landscaping

Landscaping is an essential component of all stormwater basins.

Basin Plant Selection

Plant selection should respond to specific microclimate and site conditions.

URBAN FORESTRY

Urban Forestry

Involves the preservation of existing trees and the planting of new trees during the development process.

Benefits of Urban Forestry

Benefits include the significant interception of precipitation by tree canopies and the increased water storage and infiltration capacity of the ground layer.

WETLANDS

Wetland

An area of land whose soil is saturated with water either permanently or seasonally.

Examples of Wetlands

Swamps, marshes, bogs, etc.

Main Functions of Wetlands

The main functions of wetlands are water purification, flood control, shoreline stability, and serving as reservoirs of biodiversity.

CONSTRUCTED WETLANDS

Constructed Wetlands

Constructed artificial wetland systems are highly controlled environments that intend to mimic the conditions of soil, flora, and microorganisms in natural wetlands to aid in treating wastewater effluent.

Constructed Wetlands Focus

Constructed wetlands are not primarily focused on stormwater management but more on water treatment.

Constructed Wetlands Design

They require an interdisciplinary design approach.

Tambo

A type of reed common in swampy areas in the Philippines that is used as a filtration medium.

Constructed Wetland Treatment Process

The treated water is transferred to another system. Water travels under the surface through the root system, where the reaction takes place. Eventually, the water ends up in the outlet gabion, where it is considered treated.

Wastewater Before Wetland Treatment

Before passing through the wetland, the wastewater shows an acidic character.

Wastewater After Wetland Treatment

After treatment, the pH level is neutral (7.0).