The Urbanized Effect
on Detention
Ponds
Travis
Jones, Department of Earth
Sciences,
Many innovative ideas have been proposed and implemented to correct
excess stormwater in ever-growing
urbanized areas. Fairly simple ways to
alleviate stormwater
are the development of retention ponds. These detention basins create a
permanent pool throughout the year that helps remove sediment and
pollutants
from excess runoff before entering a stream and control the outflow of
water
into streams after storms helping to eliminate flooding and regulate
runoff.
This provides a unique way of not only controlling stormwater
through watersheds but also provides an ecologically friendly
alternative to
high maintenance canals. However, some ponds were
not even
suggested to be used as detention ponds but were designated over
time.
This study measures significant water quality difference in three
different
bodies of water now being used as detention
ponds.
Three detention basins were tested weekly
for pH,
hardness, alkalinity, turbidity, and dissolved oxygen saturation. The
results
show slight differences in water quality between detention basins
located in
older neighborhoods and ones in recently developed or undeveloped
areas. While
some tested areas differed, all the detention ponds remain at adequate
and
healthy levels for aquatic life. The development and design of lakes
and ponds
with the intent of being used for Detention
provide an
efficient means to aid in runoff and flooding.
Keywords: detention ponds, urbanization
Introduction
Throughout
Detention ponds are one of two types of stormwater
ponds commonly constructed. Retention ponds are dry and fill rapidly
during a
rainfall event gradually releasing water into the watershed until the
basin is
dry again. Detention ponds are permanent pools and gradually release stormwater through an outlet structure to
adjacent surface
waters rather than through infiltration into the soils. Detention ponds
can be designed as wet or dry. Wet detention
ponds are constructed so that the pond
bottom is below the
seasonal high water table (SHWT) elevation. Dry detention ponds set the
pond
bottom above the SHWT (Dykehouse 2001).
Although, in theory, detention ponds create an
adequate way
to balance urban impacts on watersheds, the design must be appropriate
to the
situation. Poor design will significantly increase a broad range of
impacts.
These impacts include a loss of habitat by suspended silt smothering
organisms,
minimal levels of dissolved oxygen, introduction of pathogens such as
viruses
and bacteria, excessive nutrient levels that can cause an overgrowth of
algae,
increased temperatures that affect aquatic life, and a degraded
aesthetic quality
due to litter (Water Environment Federation 1992).
Many new design elements have been proposed
and most
developers are concerned with the maintenance of their detention ponds.
Karen
Jordan’s research in 2001 suggests that detention ponds benefit the
There are three lakes that I specifically looked at
due to
their location, their origin, and their surrounding area (Figure 1).
The three lakes include
The area around
The Wynnfield subdivision is a new housing
project
located off of
Research Question
Is there a significant measurable difference in turbidity, pH,
hardness, and
dissolved oxygen in the detention ponds found adjacent to older
subdivisions,
newer subdivisions, and undeveloped areas in the
Methods
Each lake was tested
for pH, turbidity, alkalinity, hardness, and dissolved oxygen content
to
determine whether these elements are high or low compared to the other
ponds of
different neighborhood concentrations. Water testing took place every
Tuesday
between the hours of
Results
The pH of
water determines the
solubility or the amount that can be dissolved
in the
water and biological availability of nutrients (such as phosphorus,
nitrogen,
and carbon) and heavy metals (such as lead, copper, cadmium, etc.). No
significant differences were found in each
lake's pH.
All lake’s pH average is 6.5 SIU with the pond at Wynnefield receiving
a
slightly higher pH than the others. This pH
level is
in the optimal range for aquatic life.
Turbid water,
appearing cloudy or
muddy, is caused by sediment, algae, and
other
particles suspended in the water. Stormwater
runoff
carries soil and debris into detention ponds from the surrounding
landscape.
Erosion of the pond’s shoreline also contributes to turbidity.
Bottom-feeding fish can cause a lot of turbidity as they stir up the
bottom
sediments in search of food. Rooted aquatic plants have a hard time
growing in
turbid water and without such plants covering the pond bottom,
sediments are more easily resuspended by
wind and
waves (Water Environment Federation 1992). Turbidity was apparently
different
in
Hardness is a
measurement of the
concentration of metal ions such as calcium, magnesium, iron, zinc etc, usually acquired as rainwater
percolates through
rock. In most water it consist mainly of calcium and magnesium salts,
with
traces of other metals(Water Environment
Federation
1992). The hardness for each lake was slightly different. On
Alkalinity refers to
the hardness derived mainly
from carbonate and bicarbonate ions and directly reflects the buffering
capacity of the water. The alkalinity showed similarities to each
lake’s
hardness count.
The final area tested was dissolved oxygen. Oxygen is essential for
aquatic
animals and plants. As water moves past their gills, microscopic
bubbles of
oxygen gas in the water, called dissolved oxygen, are
transferred from the water to their blood. Like any other gas
diffusion
process, the transfer is efficient only above certain concentrations.
In other
words, oxygen can be present in the water, but at too low a
concentration to
sustain aquatic life. Oxygen also is needed by virtually all algae and
for many
chemical reactions that are important to lake functioning. The results
were the
most significant as seen in Figure 4. Each
lake
had its own distinct DO saturation level (Figure 4). Water
temperatures in all lakes
increased and decreased at the same time during the period. The long
period of
hot, dry weather gradually increase all
ponds’
water temperature during the testing period. Water temperature directly
affects
DO saturations in that warmer water tends to hold less dissolved
oxygen.
Discussions and Conclusion
It appears that the
detention ponds in the
watershed are able to maintain a healthy life before, during, and after
urbanization. The new detention pond at Wynnefield
appears to be the healthiest. This is mostly due the new building codes
and
mindful contractors working together to produce healthy ponds that not
only
control stormwater and pollution but also
create new
and long lasting aquatic life along the watershed. However, maintenance
is
crucial for the ponds to remain at an excellent range of health. This
is evident
when compared to
Overall, detention ponds appear to have a significant impact when regulated and designed properly. New building
codes control
flooding of homes while design and outlets provide better coverage and
access
to recycling water. Other ponds and lakes naturally established should not be altered but should be able to
access outlets
to the watershed, like
References Cited
Dykehouse,
Terry. “Retention
Ponds and
Detention Ponds, The Recovery Process”.
James
Edmunds & Associates, Gainesville FL. Available: http://www.florida-stormwater.org/pdfs/pondsarticle.pdf
Accessed: March 3, 2006.
Jordan,
Karen. “The Use of Retention Ponds in Residential
Settings”. University of South Alabama
Department of Earth Sciences,
Marsh,
William. Landscape
Planning: Environmental
Applications.
Mays,
Larry. Stormwater
Collection Systems Design
Handbook.
Subdivision Regulations for the City of
Water Environment Federation. Design and Construction of Urban Stormwater
Management Systems.
Whipple,
William, et al. Stormwater
Management in Urbanizing Areas.