Karen J. Jordan, Department
of Earth Sciences,
areas are often overlooked when considering stormwater runoff.
†† Many impermeable surfaces such as streets, driveways, sidewalks,
walkways, and roofs are in residential subdivisions.
†† Retention ponds capture diverted stormwater runoff from these
surfaces. †† The ponds provide two
primary services. †† First, they retain
the runoff before releasing it into streams.
†† They release the water at flow rates and frequencies similar
to those that existed under natural conditions.
†† The flood volume held in a retaining pond reduces the impact
on downstream stormwater systems.†
The second benefit of the retaining ponds is that they provide pollutant
removal through settling and biological uptake.
† Turbidity, pH, and total hardness are tested at the retention
ponds at Charleston Pointe and
Keyword: retention pond, residential area, turbidity, Dog River Watershed
When considering stormwater runoff from impermeable surfaces, most people often overlook residential areas. † Subdivisions include impermeable surfaces such as streets, driveways, sidewalks, walkways, and roofs. † Residential areas are prone to flooding and must deal with stormwater runoff as do large commercial sites such as grocery stores, restaurants, and retail stores. †† The stormwater systems in subdivisions are just as important as commercial areas. † The stormwater systems flush rainwater quickly from streets and gutters and into the nearest waterway (EPA Victoria 2001). † Unfortunately, stormwater is not treated and often contains many pollutants including car fuel, oil, and sediments. The use of ponds as BMPís with stormwater systems in urban areas is becoming more widespread. † It is already common to see retention ponds in commercial areas. ††
†Retention ponds capture the diverted stormwater runoff from streets and gutters.† These ponds provide two primary services.† First, they retain the runoff before releasing it into streams. †† They release the water at flow rates and frequencies similar to those that existed under natural conditions. †† The flood volume held in a retaining pond reduces the impact on downstream stormwater systems (England 2001). †† The second benefit of the retaining ponds is that they provide pollutant removal through settling and biological uptake (Idaho DEQ 2001). †† Ponds remove 30-80% of certain pollutants from water before it enters nearby streams.† Common pollutants reduced are sediments, bacteria, greases, oils, metals, total suspended solids, phosphorous, nitrogen, and trash (England 2001). † Ponds are one of the most effective tools at providing channel protection and pollutant removal in urban streams (www.stormwatercenter.net 2001). †† Essentially, retention ponds provide water quality and quantity control (EPA 2001).
Two common classifications of retaining ponds are either ďwetĒ or ďdry.Ē †† Wet ponds, known as retention ponds, continually have a pool of water in them called dead storage.† Dry ponds, detention ponds, do not have dead storage and dry out between storms (EPA 2001).† Retention ponds are more effective than dry ponds.† The permanent pool of water found in the wet ponds is more efficient at removing particle pollutants.† It does this by absorbing energy from inflow of the stormwater as it enters the pond, preventing scour material from settling to the bottom, and exchanging new incoming stormwater with previously captured water. †† This provides extra time between storms for pollution to settle (Idaho DEQ 2001).† Aquatic vegetation is often associated with wet ponds.† Vegetation such as grasses and plants are able to establish themselves in the permanent pool of wet ponds thus providing extra pollutant removal. †† The aquatic plants and grasses serve as an extra filter in the pond. †† They assimilate dissolved pollutants and, by biological uptake, transform pollutants into less toxic materials. †† Microorganisms often establish themselves in wet ponds and aid in the breakdown of pollutants (EPA 2001).
There are ongoing activities within a residential setting.†† Common activities are things such as clearing lots, building houses and additions, landscaping, and the installation of swimming pools. †† Figure 1 shows †† (A) how red dirt used for a house foundation has run into the street and stormdrain after a rain and (B) fill dirt left exposed on a cleared lot.† These activities may appear minimal when compared to commercial building, but the same idea of impact should be considered. † These activities increase the possibility of sediments and other pollutants entering nearby streams.† Residential areas also pose an added threat to the stormwater system and nearby stream with common activities such as fertilizing and watering lawns, washing cars, and painting houses.† The ongoing activities within a residential area provide diverse challenges for a retention pond. ††
The area surrounding Second
Creek is growing quickly, both commercially and residentially.
†† There are a growing number of new residential subdivisions along
Surprisingly two residential
Is there a measurable difference
in turbidity, pH, and total hardness found in the inflow water versus the
outflow water of the retention ponds at
pH, and total hardness were monitored at the retention pond at Charleston
Pointe and at the pond at
††††††††††† The weekly monitoring of the ponds established a short-term trend for the project. † Measurements taken after rainfall establish the influence of stormwater on turbidity, pH, and total hardness. † The next measurement 72 hours later shows how much the ponds stabilized following rainfall.
††††††††††† A water
sample was collected at the inflow area and the outflow area of each pond.
† Each sample was collected in a 45ml test tube and taken back
††††††††††† Of the three parameters monitored during the project, turbidity showed substantial changes during the testing of the ponds. †† The fact that turbidity was influenced by rainfall was apparent. †† Turbidity is also affected by ongoing activities within the subdivisions .
Pointe currently has no houses built in the subdivision.
† No activity was recorded in the subdivision until the week of
inflow turbidity in
††††††††††† The second parameter measured was pH.†† This is a measure of how acidic or basic water is. †† Seven is considered neutral whereas values less than 7.0 are considered acidic and values greater than 7.0 are basic. †† A pH range between 6.5 and 8.5 is considered most favorable for sustaining aquatic life (Alabama Water Watch 2000). † It was found that pH did not fluctuate much during the project. †† The average pH measured at the inflow and outflow of both ponds was between 7.0 and 8.0.†††
outflow pH recorded in Charleston Pointe was usually higher than the inflow
pH (Fig. 8)
.† The higher pH recorded at the outflow
area of Charleston Pointe may be due to the large amounts of aquatic plants
and grasses found at the outflow area. ††
††††††††††† Total hardness was the third parameter measured in the project. † Water hardness is a measure of the amount of dissolved calcium and magnesium.†† These minerals are important to plants and animals.†† Calcium is important to aquatic organisms as a component of shells, bones, and cell walls.† Magnesium is a component of chlorophyll and is important for photosynthesis in plants (Alabama Water Watch 2000).†
††††††††††† A relative difference in hardness was recorded between the inflow and outflow water at Charleston Pointe.†† The inflow water measured anywhere between 40 and 60 mg/L (Fig. 10) . †† The corresponding outflow water measured between 50 and 80 mg/L. † Water that measures between 20 and 60 mg/L is considered moderately soft (Alabama Water Watch 2000).†† The higher measurements at the outflow area of Charleston Pointe may be attributed to the limestone rocks found in the area.
hardness levels in
ponds are beneficial for providing stormwater abatement and the removal
of pollutants from stormwater.†† Many
states such as
††††††††††† Retention ponds are ideal partners for residential areas within the Dog River Watershed, since the pollutant most commonly and successfully removed from the stormwater is sediment.† The retention ponds showed a measurable reduction in turbidity between inflow and outflow water (See Figures 5 and 6).†† This is ideal since one of the primary concerns with the Second Creek tributary is sediment pollution. †
††††††††††† As the areas surrounding streams and creeks in the Dog River Watershed continue to develop, the addition of ponds to subdivisions will help control concerns of sedimentation and pollution.†† Retention ponds may be included in new subdivision designs and added to already existing subdivisions.† These ponds are one of the least expensive BMP's to build when compared to others such as infiltration trenches, basins, and sand filters (EPA 1999). †† Though these ponds may be small, as a whole these ponds built in subdivisions in this area will help provide better water quality downstream in our watershed.† The use of retention ponds in residential areas should become as common as their use in commercial areas.
†† 1999.† Urban Storm
Water Best Management Practices Study.
. †† Accessed
2001.† Stormwater Issues.
††2001.† The Environmental
Impact of Stormwater Ponds.†
. †† Accessed