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AS 12 - How much stormwater makes a flood?
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Science Stage 6 – Earth and Environmental Science
Background – Impact of Urbanisation
Urbanisation in the upper Parramatta River catchment has greatly
increased the area of impervious surfaces (such as roads and roofs).
This causes rainfall that previously infiltrated into soil or flowed
off the catchment at a slow rate, to flow off the catchment quickly
and in greater volumes.
Throughout the catchment, many small creeks have been replaced
with piped and lined drainage systems. This causes additional increases
in the rate at which stormwater is carried, increased flooding and
erosion problems. The concentration of pollutants such as oil, grease,
sediment and organic matter running off urban surfaces causes deterioration
in the water quality downstream.
How much stormwater runs off your school site?
This activity involves:
- Identifying the proportions of different kinds
of ‘surfaces’ in your school grounds.
- Designing an experimental model for these surfaces.
- Measuring the % run-off of rain water from these
models.
- Calculating the volume of stormwater water running
off from your school.
- Developing strategies to reduce the run-off from
the school grounds.
1. Map school surfaces
a. Walk through the school grounds
and identify the different kinds of surfaces (for example: rooves,
paths, garden, lawn and sporting fields etc).
b. Devise a system of symbols to
represent these surfaces.
c. Use a school map and graph paper
to draw a detailed map of the various surfaces.
d. Mark on the map any systems that
your school has installed to reduce the area of impervious surfaces
within the school grounds.
e. Estimate the area of each surface
type in square metres and the proportion of each surface type in
the school grounds.
f. Record your results
in a table.
2. Design an experimental model
a. Design ‘models’ to simulate
the major types of surfaces found in your school grounds. For example
large plastic trays from the school lab could be used as containers
for the models. It could be filled with be filled with earth and
covered with a small section of grass from the school yard to represent
school sporting fields; trees and garden areas could be represented
by small branches stuck into a mulched surface.
b. Decide on how you can apply a
measured volume of ‘rain’ to the surface and how you could
measure the volume of ‘stormwater’ running off from the
different model surfaces.
3. Measure % run off
a. Conduct your experiment to determine
the volume of water applied as rain and the volume of water running
off from each surface type.
b. Calculate the % runoff for each
type of surface.
Volume of runoff x 100 = % runoff
Volume of rain applied
c. Use tables and graphs to prepare
a report of your findings.
4. Estimate school stormwater runoff
volume
a. Use this information to classify
your school surfaces in high, medium and low runoff surfaces.
b. Estimate the volume of stormwater
that would leave the school site in a storm that dropped 25mm of
rain.
(% runoff x surface area x rainfall volume
= mm stormwater volume generated by each surface type)
5. Develop an action plan
How can your school reduce its stormwater impact?
a. As a class, brainstorm
strategies to reduce the schools environmental impact on the local
creek and upper Parramatta River catchment.
b. Conduct research
into Water Sensitive Urban Design (WSUD) to assist the development
of a school action plan.
c. Prepare a report
and action plan.
d. Organise a meeting
with your school principal and school executive to report on the
results of your investigations and present the ideas developed in
your action plan.
e. With the agreement
of your school executive, it may be possible to extend your action
plan to become a “Sustainable Design” school implementation
plan.
Resources and Links
Water Sensitive Urban Design
- Upper
Parramatta River Catchment Trust website www.uprct.nsw.gov.au -
click on “Sustainable Water”
UPRCT Catchment Education Kit
- Hydrology
Information Sheet
- Flooding
Information Sheet
- ESD
Information Sheet
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