Stormwater runoff occurs when precipitation from rain or snowmelt flows over the land surface. Flooding also occurs due to excessive high intensity rainfall over the rate of infiltration of soils. All are natural hazards. Both of these problems are to be solved through water management practices. This module highlights all these aspects.

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RUNOFF MANAGEMENT
& FLOOD CONTROL
by
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore
India

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Introduction:
Runoff gathers sediment and pollutants, which
can wind up in natural waterways.
Water that doesn’t soak into soil can’t recharge
local groundwater sources.
The goal of managing stormwater runoff
includes:
Decreasing the volume and Minimizing the
pollutants.

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Decreasing runoff amount:
Prevailing Methods include
contour farming,
strip cropping,
contour barriers,
vegetative hedges).
Why is stormwater runoff a problem?
Large volumes can overwhelm storm drains and
cause localized flooding.

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Controlling the quantity and quality of
stormwater runoff.
Stormwater runoff occurs when precipitation
from rain or snowmelt flows over the land
surface.
Stormwater runoff also picks up and carries
with it many different pollutants that are found
on paved surfaces such as sediment, nitrogen,
phosphorus, bacteria, oil and grease, trash,
pesticides and metals.

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These pollutants come from a variety of
sources, including pet waste, lawn fertilization,
cars, construction sites, illegal dumping and
spills, and pesticide application.
Stormwater management is the use of specific
practices, constructed or natural, to reduce,
temporarily detain, slow down and/or remove
pollutants from stormwater runoff.

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To control stormwater runoff, it is necessary to
achieve one or more of the following:
Minimize erosion and sedimentation during
and following construction activities.
• Reduce the quantity of stormwater leaving
developing or developed sites.
• Improve the quality of stormwater leaving
developing or developed sites.

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This practice applies to sites where stormwater
runoff causes or may cause undesirable
downstream flooding, sedimentation or channel
degradation and/or degradation of surface or
ground water quality if left untreated.

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Vegetative Measures.
Where appropriate, stabilize all areas disturbed
by construction with vegetation as soon as
possible after construction.
Trees and forests improve stream quality and
watershed health primarily by decreasing the
amount of stormwater runoff and pollutants that
reaches our local waters.

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Water Quantity:
Design stormwater control systems to control
flow from the area of concern to rates and
volumes that will not cause degradation of
downstream areas due to erosion or
sedimentation.
Runoff is controlled by slowing the release of
runoff from the site.

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Stormwater runoff management is:
Slow it down, spread it out, soak it in.
Consider these affordable, do-able solutions to
do just that.
Add plants:
Incorporate plantings, especially in areas where
runoff collects.
As runoff soaks into soil, plant roots help to
absorb and filter out pollutants.

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When runoff soaks into and percolates through
soil, the soil also acts as a filter, removing some
pollutants.
Protect trees:
Like other plant roots, tree roots help absorb
and filter runoff. Tree canopies also slow
rainfall and spread it over a larger area.

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Break up slabs:
Replace concrete patio slabs with pavers,
flagstones, or bricks that allow water to soak in
between items.
For driveways, consider using turf block or
leaving a strip of grass upto the center.
Go permeable:
Choose a permeable material for a path, patio,
or driveway.

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Less expensive options include aggregate base,
gravel, mulch, or crushed shells.
Expensive options include putting a pervious
concrete or asphalt.
Catch runoff:
Install a rain barrel or cistern to catch
stormwater runoff from roofs.
Use this water to irrigate garden plants.

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Dig a trench:
Use a shallow, gravel-filled trench to catch and
slow runoff, especially at the base of a slope or
alongside a driveway or patio.
For slopes, consider creating a dry creek to
catch, slow down and direct runoff, perhaps to a
rain garden.

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Plant a rain garden:
A rain garden is designed to catch and slow
runoff.
It’s frequently planted in low areas, at the base
of a slope, or near downspout outlets.
The design includes soil layers, mulch, and
plants, all of which filter rainwater as it seeps
into soil.

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Cover the soil:
Depending on the type, bare soil can be like
concrete in terms of its ability to absorb water.
Cover bare soil with mulch or a ground cover to
slow stormwater runoff.
Swap the lawns:
Trade turf for native plants, which are adapted
to local growing conditions and require fewer
inputs (once established) than turf.

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Drive on the grass:
If your driveway isn’t permeable, wash your car
on the lawn so water can soak into soil, instead
of running into the street.

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Flood control
Flood control refers to all methods used to
reduce or prevent the detrimental effects
of flood waters.
Floods are caused by many factors (or a
combination of factors.
The notable ones are heavy rainfall, highly
accelerated snowmelt, severe winds over water,
unusual high tides, tsunamis, or failure of

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dams, levees, retention ponds, or other
structures that retained the water.
Flooding happens due to increased amounts of
impervious surface or by other natural hazards
such as wildfires, which reduce the supply of
vegetation that can absorb rainfall.
Periodic floods occur on many rivers, forming a
surrounding region known as the flood plain.

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Impacts of Flooding:
Flooding damages the property and endangers
the lives of humans and other life.
Rapid runoff of water causes soil erosion and
concomitant sediment deposition elsewhere
(such as further downstream or down a coast).
The spawning grounds for fish and other
wildlife habitats can become polluted or
completely destroyed.

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Some prolonged high floods can delay traffic in
areas which lack elevated roadways.
Floods can interfere with drainage and
economical use of lands, such as interfering
with farming.
Methods of controlling floods:
Flood control refers to all methods used to
reduce or prevent the detrimental effects
of flood waters.

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Flood relief refers to methods used to reduce the
effects of flood waters or high water levels.
Some methods of flood control have been
practiced since ancient times. These methods
include planting vegetation to retain extra
water, terracing hillsides to slow flow downhill,
and the construction of floodway.

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10. Methods adopted to control floods:
Inundation methods and Flood diversion.
Causes of floods/ effects of floods/ flood
hazards. The inundation of land and property is
a major effect of a flood.
Such impacts depend on many factors such as
depth and duration of inundation, flow velocity,
and the various flood-generating factors.

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Methods of controlling floods:
Dams/ Water-Gate/
Diversion canals/
Self-closing flood barrier/
River defences/
Coastal defenses/
Temporary perimeter barriers/
Property level protection.

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Types of flood control on rivers:
Channel Conveyance Changes
Levees
Reservoirs
Floodways.
We need to introduce better flood warning
systems.
Construct buildings above flood levels.

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Protect wetlands and introduce plant trees
strategically.
Restore rivers to their natural courses. Improve
soil conditions.
Introduce water storage areas.
Put up more flood barriers.