Ideally, the internal levee should maintain a factor of safety of above 1.4, and as such, the maximum back flooding of the system will be will be MSL + 6 ft. Table 3 shows that for different river water levels increasing the back flood water levels results in a increase in the the factor of safety of the levees. While there are minor variations to this trend, the levee becomes more stable with increased back flooding. This result supports the theory that the hydraulic exit gradient resulting in piping and slope instability can be reduced by the Water Management System. The optimum back flooding levels from simulations of various elevated river conditions are highlighted in Table 3. Significantly higher factors of safety for the existing sections of the Sherman Island levees can be achieved with these levels of back flooding resulting in greater levee stability and lower risk of failure from river flooding. The driving forces for levee and piping resulting in slope failure stems from high exit gradients.As pressure builds up on one side of the levee, stacking flower pot tower water is forced towards the backside of the levee and thus increases the hydraulic gradient. This increases the already high hydraulic gradient of the peat layer even further.
The addition of the temporary flood storage zone allow for siphoning water to balance water levees on each side on each side of the level. Therefore the exit gradient and pore pressures are decreased leading to a significant increase of the stability of the levees. Figure 7 compares the exit gradient for an 8+MSL flood level and back flooding of 2+MSL which indicates a reduction of the exit gradient by approximately half.Site work estimates consider the construction costs of internal cutoff levee and necessary road improvements for site access. The cutoff levee requires approximately 440,000 cubic yards of fill at $15 per cubic yard, therefore the total cost of the levee is approximately $6.6 million . For project access, revitalization of a portion of the former Victory Highway is the most likely option. The approximate length of road to be improved is 0.54 miles with an estimated cost of $1.8 million per mile constructed . This value reflects construction equivalent to a one-foot asphalt concrete layer and gives a total of approximately $972,000. An alternative route involving revitalization of a larger portion of Victor Highway stretching roughly 2.17 miles would cost $3.9 million, which is four times the cost of the first option. The total materials cost for the aquaponics system is approximately $23 million. This includes 600 aquaponics subsystems at $30,000 to $50,000 each, with an average of approximately $38,500. The prices of hydroponics and aquaculture components, including: tanks, pumps, anchors, and rafts per subsystem.
The prices are based on data from UVI Aquaponics, CropKing Hydroponics, Dock Float Supply, Dock Builders Supply and Seaflex Anchors. Labor and construction costs are not included as further design and bidding by licensed aquaponics contractors are needed. The cost of wetland development is extremely variable depending on the scale of the project and quality of labor and materials used. According to Dr. Alexander Horne, estimates for wetland construction range from $2,000 to $75,000 dollars per acre . For the purposes of this project, Dr. Horne recommends a value of $25,000 per acre of wetland constructed. Therefore for 700 acres of wetland restoration there is an initial cost of approximately $17-18 million. Operations & Maintenance The economic analysis of sturgeon production by Logan estimates costs of operations and maintenance per aquaculture system at approximately $3,500 to $4,000. This includes cost of labor, feed, electricity, and medicine. Assuming a 25 percent increase in these costs to account for agricultural labor, this results in operating and maintenance costs between $4,000 and $5,000 per subsystem. Consequently for the 600 systems proposed there is an annual cost of approximately $2.8 million. For the proposed system on Sherman Island, there are three chief sources of revenue. The first is the sale of agricultural yields from the hydroponics component. The second is the sale of fish yields from the aquaculture component. The third source is the economic value placed on various wetland services.
Income generated by agriculture is dependent upon the type of crop produced as well as the frequency of harvesting cycles. For the purposes of this model, it is assumed that average yield is approximately 11,000 pounds of crop per year per system. Price indices for crops typically used in aquaponic operations indicate that cilantro has the highest economic benefit of $88,000 per year, with onion having the lowest value of $1,100 per year. On average, each year of production will generate roughly $25,000 to $30,000 in revenue per subsystem, resulting in nearly $17 million of income over a two-year time period. The aquaculture component of this business model uses price indices developed for similar systems rearing sturgeon. Numbers generated from previous examples include considerations for 5, 10, and 15 brood stocks. There is a harvest time of 18 months for each system, and production will likely be staggered to produce maximum output and more continuous income for the project. Considering a time period of two years, fish production gives estimated revenue of roughly $17 million assuming a sale value of $4.5 per pound of sturgeon. Wetland value is based on a sum of averages of the following services: gas regulation, disturbance regulation, water regulation, water supply, waste treatment, habitat, food production, raw materials, recreation, and cultural ecosystem services . Revenue for these services is presented in Table 4.The wetland component of the system will provide carbon sequestration. Carbon sequestration is the capture of atmospheric CO2 by plants such as bulrushes and cattails through photosynthesis. The Bulrush wetland can grow approximately 500 g C/ m2 per year, half of which is preserved. The CO2 is absorbed by the plants and then incorporated into the soil biomass as the plants decay over time. A wetland can sequester as much as 25 metric tons of CO2 per acre per year. This helps to reduce carbon emissions while reversing subsidence . The system actively stops and reverses subsidence. By flooding the area with water the peat layer preserved because it is wet. As the plant biomass from the wetland decomposes it increase the peat layer and therefore reverses subsidence. Wetland vegetation and non-sellable crop yields from the hydroponics system can be used to restore peat. Similar subsidence reversal projects have been proposed and approve on and around Sherman Island. One such project includes Twitchell Island Ponds where an increase of 1.6 inches/year in addition to preventing subsidence of approximately 1 inch/year has been demonstrated. During flooding even there will be sediment will be transported into the system and then settle out before the water in release back into river. Therefore sediment can slowly build up with flooding events and also reverse subsidence .
In addition the wetland restores natural habitats for birds and aquatic species. The fish a reptile species that would take advantage of this wetland ecosystem include carp, crappie, striped bass, white catfish, and pond turtles. Along with hundreds of different bird species including the mallard duck, red-tailed hawk, eagle, Canadian goose, cinnamon teal, ring-necked pheasant, ruddy duck, wood duck and many more. The wetlands will serve to restore the delta wetland habitats as well as to sustain future bio-diversity of wetland species . Water contamination and waste is reduced by the aquaponics system because nutrients and water are recycled back into the system through water recirculation. This separation of the system from the surrounding environment reduces water waste due to runoff and agricultural pollution when compared to terrestrial agriculture. Terrestrial agriculture requires a large amount of water,ebb and flow the majority of which is not absorbed by plants but leaves the land via groundwater runoff. Agricultural runoff promotes algal blooms and eutrophication, which lower the oxygen concentration dissolved in the water and leads to death of aquatic species. The potential environmental concerns of the wetland include the production of methane from biomass decomposition. While wetlands sequester carbon and hence reduce carbon dioxide, they release other GHGs, primarily methane and nitrous oxide . The concern is that Methane has a Global warming potential 21 times that of CO2, and N2O has a GWP 310 times that of CO2. Most of the GWP of CH4 occurs in the first twelve to fifteen years after its release, whereas the GWP of CO2 lasts decadnto the water within the system and the transport of such toxins into the surrounding environment. The soil at Sherman Island has been exposed to pesticides, fertilizers, and dredged soils for the bay which were contaminated with heavy metals. Therefore because the proposed design is to partially flood the soil the toxins could leach from the soil. In order to mitigate this possible issue a test flood plot an monitor the toxin release levels. Leach test or Barrel tests can be used to mimic the conditions and will give results that can be used to assess further needs of mitigation. Additionally, the heavy metals such as the metals off of ships including copper, zinc, and nickel can be immobilized in wet peat soils.
Organic compounds will bind to peat and once the wetlands have been established the plants will also remove toxins from the water. Finally because the flood storage zone will contain a large volume of water the toxins will be diluted. There may be short term effects from pesticides so to prevent birds from being exposed to these toxins the use of bird scaring devices can be implemented until toxins diffuse. It is important to monitor the toxins before, during and after the installation of the wetland in order to understand the mitigation strategies that must be considered and implemented. Many of the environmental concerns can be monitored at demonstration sites including Mayberry Farms Subsidence Reversal and Carbon Sequestration Project and the Twitchell Island Ponds which both contain many of the same environmental considerations that will be faced in the flood storage zone. Fatty acid composition was determined in leaves of purslane plants exposed to saline treatments for 30 days. A sample of 50 g of fresh tissue leaves was dehydrated in a incubator at 60 ºC for 48 h. The dehydrated tissue was macerated and stored in 15 ml vials at room temperature, protected from light. An aliquot of 1 g of each sample was used to determine fatty acid composition, according with the procedures described by Liu, et al. . After hexane extraction, the samples were vortex-mixed, centrifuged, and the upper phase was collected prior to GC analysis. Samples were injected via an auto sampler onto a fused-silica capillary column in a HP 6890 gas chromatograph system fitted with a flame ionization detector and eluted with helium at 44.0 ± 1 ml/min, with a split ratio of 1:17. The injector and detector were heated to 250 ºC. The column was temperature programmed from 130 ºC to 180 ºC at 25 ºC/min, and then to 230 ºC at 2.5 ºC/min. Fatty acid methyl esters were identified by comparing GC retention times with those of a mixture of standard fatty acids methyl esters Mix C14-C22, . Fatty acids were quantified using peak areas integration against internal standard. In GL and GR cultivars, submitted to 30 days of saline treatment, the main fatty acids detected were C16:0, C18:3 and C18:2. Such high amounts of palmitic acid, has it was found in the P. oleracea leaves of control plants is unusual, previous studies reported an proportion of 17% of this fatty acid in the total FAMEs detected . Palmitic acid, the most abundant fatty acid in the human diet, causes oxidative DNA damage, DNA strand breakage, necrosis and apoptosis in human cells in vitro, but when consumed with others fatty acids, like PUFAs, is unlikely to have any significant impact on human health. The amount of unsaturated fatty acids was also a little bit lower than expected, although the proportions between UFAs and SFAs were maintained ; it has been reported in other studies that the linolenic acid content in P. oleracea leaves was circa 50% of total fatty acids and linoleic acid content 3- 4 times lower.