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Types of Constricted Storm Water Wetland

Shallow March system

Normally, marsh wetlands include marsh zones containing standing water depths ranging approximately 18 inches during dry or normal climatic conditions. Such zones as mentioned by NJDEP (2004, p.6) are configured further as high as well as low marsh components. Basically, the marsh wetlands are supposed to have sinuous pathways in order to improve the contact area and time of retention. Marsh wetlands according to NJDEP (2004), need an enormous site area as compared to other forms of constructed stormwater wetlands. Marsh wetlands need larger drainage areas in order to achieve the required flow rate of the base as well as groundwater that could facilitate the reduction of mosquito breeding and support emergent plants. This greater area needs larger normal inflow rates so as to produce the required rates of volume changeover and flow velocities NJDEP (2004, p.6). Shallow marsh wetlands comprise of aquatic vegetation having a pool that ranges between 6 and 18 inches during normal weather conditions.Craft (2015, p.100) posits that shallow marsh wetlands are created in a way that flow is uniformly conveyed through the wetlands towards the area of treatment. Although the varied water depths such as streams or pathways improve the value of wetland’s ecosystem and aesthetic, DEEP (2004, p.2) posits that they can result in wetland short-circuiting; thus, leading to the reduction of the treatment effectiveness. Therefore, treatment performance in shallow marsh wetlands can be maximized by offering a system that is uniformly sloped. Furthermore, the plug flow conditions can be improved across the shallow marsh wetland by constructing wetland cells and separating the cells using weirs. Shallow marshes need greater contributing drainage areas since the volumes of runoff are mainly stored in the marshes (Metropolitan Council, 2002, p.229). Figure one shows a schematic design of a normal shallow marsh wetland.

By Name

Figure One: Shallow Marsh Wetland
(DEEP, 2004, p.3)

Pond wetland system

Pond wetlands according to NJDEP (2004, p.5) include ponds that have standing water depths that range between 4 and 6 feet in climatic conditions. At least one component of pond together with low and high marshes is used in the pond wetlands. NJDEP (2004, p.5) asserts that the pond is the component normally utilised to remove particulate pollutant from the runoff. The forebay improves the pond’s removal ability and also decreases the runoff’s velocity while flowing into the wetland
(EPA, 1993, p.113). Furthermore, the marsh zones offer extra runoff treatment, especially for pollutants that are soluble. The site area required by pond wetlands is much smaller than the shallow marsh wetlands. Importantly, the pond wetlands have a higher rate of pollutant removal as compared to other systems. The pond wetland system has a number of limitations; for instance, when the pond wetland is located improperly, its construction could result in the loss of high-quality forest or natural wetlands. Even though the pond wetlands use a small site area in relation to their drainage areas, their effectiveness in dense urban areas is very low due to that fact that the pond could be somewhat bigger. Furthermore, the utilisation of pond wetlands is limited in the semi-arid and arid because of the necessity to enhance the permanent pool. Pond wetlands are also less feasible in cold water because of the likelihood of stream warming (Stormwater Manager’s Resource Center, 2001). Figure two shows a schematic design of pond wetland.

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Figure Two: Pond Wetland (DEEP, 2004, p.9)

Extended Detention Wetland

Extended detention wetland is different from shallow marsh and pond wetlands because it stores a certain percentage of the runoff volume temporarily in the semi-wet zone; thus, exceeding the normal level of the standing water. By storing runoff temporarily, the extended detention wetland allows the utilisation of marsh zones and pools that are somehow smaller. For this reason, the site area required by the extended detention wetlands is very small as compared to that of marsh and pond wetlands. Furthermore, the time of detention in the extended detention wetland’s semi-wet zone should not be below 24 hours. The utilisation of the semi-wet zone results in increased levels of water in this type of wetland during the storm events as compared to other systems. For that reason, the wetland vegetation area is likely to expand above the normal standing water levels that the marsh and pool zones occupy (NJDEP, 2004, p.6). Furthermore; the extended detention wetlands offer an improved protection of the downstream channel since they are designed with additional vertical storage volume. This extra storage capacity offers additional detention of runoff, which exceeds the normal elevations of the pool. Extended detention wetlands have some limitations; for instance, they could become a mosquito breeding ground and can result in habitat destruction at the time of construction. Furthermore, their pollutant removal rates are moderate and cannot remove soluble pollutants effectively (Stormwater Manager’s Resource Center, 2001). Figure three shows an extended detention wetland.

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Figure Three: Extended Detention Wetland (DEEP, 2004, p.5)

Work Cited

Craft, C., 2015. Creating and Restoring Wetlands: From Theory to Practice. London: Elsevier.

DEEP, 2004. Connecticut Stormwater Quality Manual: Stormwater Wetlands. Manual. Connecticut : Connecticut Department of Energy & Environmental Protection.

EPA, 1993. Handbook: Urban Runoff Pollution Prevention and Control PLanning. Collingdale, PA : DIANE Publishing.

Metropolitan Council, 2002. Constructed Wetlands Stormwater Wetlands. Manual. Saint Paul, Minnesota: Barr Engineering Co. Sustainable Sanitation and Water Management.

NJDEP, 2004. Standard for Constructed Stormwater Wetlands. In New Jersey Stormwater Best Management Practices Manual. New Jersey: New Jersey Department of Environmental Protection. pp.1-12.

Stormwater Manager’s Resource Center, 2001. Stormwater Management Fact Sheet: Dry Extended Detention Pond. [Online] Available at: http://www.stormwatercenter.net/Assorted%20Fact%20Sheets/Tool6_Stormwater_Practices/Pond/Dry%20ED%20Pond.htm [Accessed 16 October 2016].

Stormwater Manager’s Resource Center, 2001. Stormwater Management Fact Sheet: Wet Pond. [Online] Available at: http://www.stormwatercenter.net/Assorted%20Fact%20Sheets/Tool6_Stormwater_Practices/Pond/Wet%20Pond.htm [Accessed 16 October 2016].