Interface and treatment model
Total suspended solids
The wetland gross pollution
The wetland has all the features of free water surface constructed wetland. It resembles a natural wetland because water flows over the leaves of the plants that are rooted in the soil. In contrast, the submerged bed wetlands have water flowing underneath the surface of media such as rock and gravel. The wastewater in the latter does not stand and is not visible from the surface. As such, this design will consider the wetland as a free water surface.
In the analysis, we will assume a depth to width ratio of 2: 1 as per the Virginia storm water design manual volume number 13, 2011.
The inlet area takes up a small portion of the wetland and can be calculated from:
Q=0.00278CiA where C=0.5hr
Therefore Q=0.00278x 0.5x 0.0141m/hrx 6000m2=11.76 cubic meters per hour
Area required for the inlet zone is given byQ/vS
Taking the velocity of the medium sand in the calculation=0.66mm/s
11.76/ 125×2=0.05 square meters
Different notional detention period
The default notional detention time in this analysis is 0.149 hrs. The notional detention period is dependent on the extended detention depth which in this case is 1m Therefore, a change in this depth results to a change in the notional detention depth.Changint the depth to 2.00m results to a notional detention time of 0.211 hrs. In essence this means that an increment in-depth results to a reduction in the detention time. Moreover an increase in the notional detention time has the effect of increasing the pollutant load concentration.
Epheneral wetland system
Re-use of wetland water
Wetland and change in notion al detention period
Epheneral wetland system
Wetland water re-use
Bioretention system for low discharges
The optimal wetland design considerations are based on the total land area available. The inflow determines the pollutant load delivered and if this area is large proper design considerations need to be made.However the use of a bioretention basin for polishing will serve the purpose of removing the extra pollutant loads contained in the effluent from the wetland.It may not be advisable to use the watet for reuse unless a proper methodology of removing the pollutants from the wetland is devised.
Information regarding the increase in porosity as well as the pollutant loads have an effect of changing the whole design criteria.40% of the houses draining the rainwater to a tank means that there is a reduction in the amount of water being delivered to the wetland.However, the design team has to consider the type of sewer system.Separate sewer systems have different channels for transporting stormwater and residential effluent while a combined system does not.Therefore, the effects of draining stormwater into a tank are likely to be felt more in a combined system than a separate system
Nevertheless, the design will be affected because of the amounts of influent from the residency.The total draining area used in the model will need to be reduced to cater for the diversion.