OPTIMAL ECOLOGICAL MANAGEMENT PRACTICES (EMPs)
6.2. SCOPE OF APPLYING EMPs AND OPTIMIZING EMP COMBINATION
Release and transport of nonpoint source pollutants from the catchment can be controlled to a great extent in a sustainable way through land management practices. While emphasis is increasing on structural measures, like pond, retaining wall, etc non structural measures can also be used for controlling non point source pollutants and water yield. A judicious combination of structural and non structural measures can provide a sustainable
solution to the problems that arise due to increase release of runoff and non point source pollutants from the upper catchment.
Based on this idea, the concept of Ecological Management Practices (EMPs) has been developed, which can be defined as eco friendly sustainable management practices used for maintaining and enhancing land-uses in a natural way. In other words, EMPs are basically sustainable measures that consist of combination of different structural and non structural land management practices adopted for controlling runoff volume and yield of sediments and other pollutants from an area and transport of the same by the runoff.
EMPs like contour terracing, mulching, grass, shrubs, detention/retention pond, buffer zone with vegetation and tree, sediment trap, rainwater harvesting systems and vegetated waterways are commonly used for controlling sediment yield and runoff volume from land surface. One of the natural land covers, wetlands and swamps were observed to be a good non point pollutant trap (Robb, 1992; Smith, 2001). Knowing the effectiveness of wetlands to control non point source pollution, construction of wetlands as a pollution control measure was also suggested by Wang et al., (2006) and Moreno et al., (2007).
Besides, some studies have also reported effectiveness of detention pond in controlling non point pollution like sediment and nutrient. Hsieh and Yang (2007) used optimization method and an annual average reservoir water quality model to develop optimal Best Management Practice (BMP) strategy for controlling non point pollution in the Fei-Tsui Reservoir watershed; they suggest installation of several detention ponds in the watershed to attain oligotrophic conditions in the reservoir. The riparian buffer zones with grass and forest were also reported to be effective in controlling non point source pollution in some of the recent studies by Anbumozhi et al. (2005), Shiono et al. (2007) Maillard and Santos (2008) and Parajuli et al. (2008). Besides the traditional practices, some new ideas on
landuse management practices like wood filters (Boving and Neary, 2007) and biofilter (Hatt et al., 2009) for controlling non point pollution have also immerged in recent years
Suitable EMPs for urban areas
While many investigators have reported successful application of land management practices for controlling non point source pollution, study towards application of such practices in urban sector is limited. So far, there is no well established EMP recognized as suitable for urban residential developments. However, various traditional land management practices as described in the previous section are available for controlling sediment yield and runoff volume from agricultural areas. These practices, if suitably modified considering the necessity of an urban area, can also be used for land management of urban residential areas. Some of possible EMPs for urban residential areas are suggested below:
(i) Grass land: Grass reduces the velocity of surface runoff, minimizes the impact of rain on soil, and its root system helps in increasing infiltration. In urban area, grass land can also serve as open land that is needed according to the municipal rules.
(ii) Forest land: Tree canopy reduce the direct impact of rain on soil. Besides, forest land, covered with falling leaves, also reduces the surface runoff velocity and increases infiltration. Falling leaves and decaying branches act as mulches and thus tree cover can control sediment yield and runoff volume.
(iii) Covering rain impacted areas with pebble, vegetation or wood chips: Erosive power of rain drop depends on size of rain drop and its falling height. Size of rain drop that falls from inclined roof of a house become quite large and thus strikes the ground with very high erosive power. Thus, the portion of ground lying below the line of the roof edges is prone to more erosion as the accumulated rain over the roof falls with a high velocity and with larger drop size. Such drop line areas of water around the house can be covered with pebble or wood chips or erosion resisting
vegetation can be allowed to grow, which protect the soil from the direct impact of rain drop and also allow more infiltration.
(iv) Detention drain and Retention pond: To capture the excess surface runoff, detention drains can be constructed across the slope and retention ponds can be constructed in a suitable location. This can minimize downstream erosion and flooding.
(v) Vegetated waterways: If the paths (or channels) of accumulated surface runoff are covered with vegetations, then the vegetation provide an obstruction to the flowing water. It reduces velocity and hence the erosive power of the flowing water. This reduces erosion of channel bed and bank and prevents gully formation. Root systems of a vegetated waterway not only increase bondage of soil and make it resistant to water erosion, but also promote infiltration. Depending on the status of degradation of the waterway, different types of vegetation can be suggested.
(vi) Rainwater harvesting system: Rainwater harvesting is a technique of collection and storage of rain water in surface (storage tanks) or sub surface aquifer before it is lost as surface runoff. Rainwater harvesting system helps in reducing the peak runoff and also recharges ground water. The collected rainwater through the rainwater harvesting system can also be used during the period of water shortage.