Design Package
Conceptual Drawings
Figure 8 - Typical surface flow constructed wetland
Figure 8 Shows the suggested wetland design. The designed wetland begins by slowing the initial velocity of the inflow with a rock bed. The flow then continues to slow through a multi-functional forebay that provides a trench like area that not only decelerates the water, but also provides a mosquito dead zone: the forebay is too deep for mosquitoes to lay their eggs. Continuing down the wetland the flow will be hit with an assorted array of plants located in the inundation zone. Once the flow reaches the deep pool it’s held behind the weir where the velocity is controlled and the water is passed along through a vegetated polishing channel, where it will go through a final treatment process. In the event of a hundred year storm an emergency spillway has been added to the side of the deep pool that naturally leads the water back to the lake.
Figure 9 - 7.5 degree digital elevation map of site and surrounding area
Figure 10 - Plan view of constructed wetland
With the constructed wetland's available area limited by residential development and topography, a wetland configuration as shown in Figure 10 was selected. The approximately three acres of available area constitutes less than the recommended 3% of the contributing watershed's total area, but the group has determined this to be the most suitable location for the wetland.
Upon entering the wetland, the water will be slowed by a cobble channel before entering the forebay. The forebay is important because it prevents the constructed wetland from clogging with sediment over time. The majority of the constructed wetland’s area will consist of a shallow pool for contaminant removal where a design wetland pool depth of approximately 23 inches was calculated. Depth calculations were completed using the following method:
Hunt Water Balance Equation
According to surface flow wetland design standards, the wetland should have deeper pools which occupy atleast 25% of the wetland's available area. These can be seen in Figure 10, and are labelled the "deep pool" and "forebay". Additionally, 70% of the wetland area should be a "High Marsh Zone". This is labelled in Figure 10 as the "wetland pool". Finally, the wetland is permitted to have one "transition zone." This is where the flow transitions from the deeper pools to the high marsh zone. This area is shown between the forebay and wetland pool.
Review of Local Property Boundaries
Figure 11 - Easternmost lot shared with constructed wetland site (Lexington PVA)
Figure 12 - Westernmost lot shared with constructed wetland site (Lexington PVA)
Determining the local property lines was an important part of choosing a location for the constructed wetland. By doing this, the group was able to determine which pieces of land were available and which were owned. Around the lake, all of the land is owned by independent homeowners except for the plat in Figure 12. The group selected this site as the most likely to receive approval to construct the wetland because the lot is controlled by a trust. This being said, this parcel of land is not large enough to accommodate the preferred wetland size, so the project design was scaled down.