Preliminary Engineering Report Design and Cost Analysis of the Comprehensive Everglades Restoration Plan Southern Reservoir

Transcription

1 Preliminary Engineering Report Design and Cost Analysis of the Comprehensive Everglades Restoration Plan Southern Reservoir Prepared for: The Everglades Foundation Data calculations and analysis contained in this report are correct to the best of our knowledge and belief while following generally accepted engineering practices. The calculations are in accordance with appropriate principles of standard engineering practice. Ardeshir Tehrani, PhD, Eng. Emmanuel Cruz, Eng. Ardeshir Tehrani, PhD, Eng. July Bolsover sky Ct, Katy, TX Emmanuel Cruz, Eng W Peachtree St. NW, Unit 2214, Atlanta, GA Page 1 of 17

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3 1. Introduction This engineering document report the preliminary design of an Everglades Agricultural Area (EAA) southern reservoir. This document is at a conceptual level and the final configurations, sizing and other details of the reservoir will be refined during the design process to maximize cost efficiency while meeting the project s goals and objectives. The EAA Storage Reservoir concept is an integral part of the Comprehensive Everglades Restoration Plan (CERP). Ecological restoration of the Everglades will require a significant increase in the quantity of water made available or retained for the natural system. The goals of the EAA Storage Reservoir Project are: Improve timing of environmental deliveries to the Water Conservation Areas (WCAs) including reducing damaging flood releases from the EAA to the WCAs, reduce Lake Okeechobee regulatory releases to the Caloosahatchee and St. Lucie estuaries, and meet supplemental agricultural and environmental demands for water supply. Additionally, the reservoir will improve the performance of STA 3/4 by acting as surge tanks to equalize flows. The EAA reservoir will also improve water quality by providing residence time for settling of contaminants prior to input into STA 3/4. The selected modeled EAA storage reservoir features one reservoir impoundment with a maximum normal pool storage depth of 6 feet at approximately 60,000 acres of aboveground surface area storage. The reservoir is divided into two cells, Cell 1 and Cell 2, approximately 30,000 acres each in size. Both reservoir cells include individual inflow pump stations, discharge structures, emergency overflow spillways, and seepage control canals with associated structures. 2. Project Site The Everglades Agricultural Area (EAA) consists of approximately 500,000 acres located immediately south of Lake Okeechobee. The Southern Reservoir Storage consists of two adjacent cells separated by an interior levee structure. Cell 1 is rectangular in shape and covers approximately 33,300 surface acres, while Cell 2 is roughly rectangular in shape and covers approximately 29,760 surface acres (Figure 1). The project area is bounded on the south by STA 5/6, Rotenberger, and A2 Talisman land. The reservoir is surrounded from all the remaining sides by active farm lands. Page 3 of 17

4 Figure 1: Location of the EAA southern reservoir. Page 4 of 17

5 3. Design of the Reservoir a. Scope of Project The purpose of this document is to calculate the appropriate reservoir footprint, and its corresponding maximum levee to levee distance, and reservoir height, with respect to the wind fetch and the corresponding wave run-up. The embankment earthwork could then be recalculated for the EAA southern reservoir to determine the optimum levee height. Results from this analysis do not constitute a recommendation for a final levee height design. Figure 2: Earthen Levee Cross-Section (not to scale). b. Calculation Methodology In the Central and Southern Florida Project, Everglades Agricultural Area Storage Reservoirs report published by the US Army Corps of Engineers (USACE) and South Florida Water Management District (SFWMD) in 2006, wind setup and wave height were calculated for a reservoir in the EAA [1]. In this report, the authors determined the wave parameters for two selected parcels of land, as shown in Figure 3, according to: the fetch distance, wind speed, and maximum pool depth. The reservoir considered in the present report is located nearby the previously analyzed cells in the USACE report [1]. However, the size of the reservoir cells considered here are not similar to the ones analyzed previously [1]. Consequently the fetch distance and the maximum pool depth are also different, therefore, the wave parameters should be re-calculated accordingly. Fetch distance determination Page 5 of 17

6 Fetch is defined as a distance over which the wind speed and direction are reasonably constant. Fetches fall into two categories, open-water fetches, where wave growth is limited only by the incident meteorological conditions, and restricted fetches, where wave growth is limited by a confined geometry such as that of a lake, river, bay, or reservoir. The EAA reservoir is subject to a restricted fetch. The restricted fetch methodology applies the concept of wave development in off-wind directions and considers the shape of the basin. The fetch is defined as the radial average over an arc of 24 degrees centered on the wind direction. For the present study, the wind direction is assumed to be the direction corresponding to the maximum fetch distance. This will provide the maximum design fetch lengths for determining the maximum possible duration. Figure 3 indicates the 24-degree arc for each cell, divided into 3-degree intervals. Averaging the radial lengths over each arc gives average fetch lengths of 43,500 ft and 32,520 ft for Cell 1 and Cell 2, respectively [1]. Figure 3: Fetch Determination Schematic for Cell 1 and Cell 2 [1]. The wind setup values for the abovementioned cells, corresponding to the maximum surcharge pool depths in each cell, are provided in the following table obtained from [1] Table 1: Wind Setup Values. Page 6 of 17

7 Maximum Wave Height The process of wind wave growth (assuming initial still water) begins with the motion of the air above the water disturbing the surface of the water. As wind begins to blow over the water, wind stress at the air-water boundary leads to the formation of small perturbations in the water surface. When the perturbations become large enough to affect the pattern of air flow a transfer of momentum and energy between the air layer and the water surface occurs, rapidly increasing wave heights. Wave heights build rapidly over a relatively short distance, increasing at a rate that varies dependent upon wind speed. Waves develop more quickly and with greater uniformity as wind speed increases. Waves in both Cell 1 and Cell 2 of the EAA reservoir experienced relatively uniform growth prior to breaking on the bench fronting each of the levee embankments. Resulting maximum significant wave heights (post-breaking) at the down-fetch levee face and corresponding peak wave periods for each of the two computational grids, for each wind speed and depth condition are provided in Table 2. Table 2: Maximum Significant Wave Height. Computational Grid Maximum Wave Height (ft) Peak Wave Period (sec) Cell 1: 12 ft Normal Pool (101.2 mph) Cell 2: 12 ft Normal Pool (101.9 mph) In order to study the effect of depth on the wave parameter, the wave frequency for intermediate water depth is a function of wave number (or length) and water depth. For Linearized (Airy) Wave Theory, this relation can be expressed as follows [2,3]: 2 2 ω = gk.tanh( kd) (intermediate water), ω = k gd (shallow water) The effective fetch, simple fetch, and spectral contribution methods allow the user to select the relationship of wave height and period to fetch and wind speed. The equations derived from the JONSWAP experiment are commonly used [4,5]: 4π 7 W , 3 h = U X g Wt = UX g Page 7 of 17

8 After estimating and adjusting the wave height and time period, the wave run-up over the reservoir slope can be calculated. For this purpose, the methodology presented by Steven Hughes [6] in estimating the wave run-up on smooth slopes using the wave momentum flux parameter is employed. Briefly, two approaches are used as regular wave run-up and wave momentum flux factor are measured. The maximum between the two methods is considered for the levee height. c. Reservoir footprint The reservoir volume is set at 360,000 ac-ft with an initial depth of 6 ft. The required footprint under those conditions is at 60,000 acres. The reservoir shown in Figure 1 should be divided to at least 2 cells in order to decrease the wind fetch distance, and consequently the wave height. The land shape is overall rectangular; hence, the cell section cut for cells is decided at the middle of the North-South edge, as shown in Figure 4. If either Google Earth or relative edge ratios is used, one can come up with the following edge lengths, as depicted in Figure 4. The most critical compartment is Cell1, because its chord is the longest one, and is about 10.3 miles. Figure 4: Reservoir Configuration. Therefore, the reservoir cells areas are: A Cell1 = 33,300 acres, A Cell2 = 29,760 acres Total area of cells = A Cell1 + A Cell2 = 63,060 acres Total perimeter by removing the sharing edge = 42 miles d. Wave Run-up and Reservoir Height Estimation of the wave parameters According to the literature [3], the wave period and height are affected by the water depth. The parameters of wave generated by wind are calculated based on the reservoir depth that is 16.3 ft [2]. The wind fetch distance and wind condition for both cases are the same; but because the depth decreased from 16.3 ft to 10.3 ft; thus, the wave height and period should be re-estimated following the change in depth. The wave height is impacted by Shoaling Coefficient, which is a Page 8 of 17

9 function of the water depth to wave length ratio. Here, we assumed that the wave length generated by wind is the same for both cases. Margin Ratio of Shallow Water Condition: dl = Water Depth to Wave Length Ratio Parameter: Shoaling Coefficient for 16 ft Depth: 16 ft L = 0.05 X!" = 2 πdl = K!!" = tan X!" + 2X!" cosh (X!" ) = 0.95 Water Depth to Wave Length Ratio Parameter: Shoaling Coefficient for 10 ft Depth: X!" = X!" = K!!" = tan X!" + 2X!" cosh (X!" ) = Re-estimated Wave Height (for 10 ft): W!!" = W! K!!" K!!" = 2.7 ft Moreover, the wave frequency for intermediate water depth is expressed as follows, which is a function of wave number (or length) and water depth: w! = gk. tanh (kd) For the shallow water condition, the recent equation is simplified to (dl < 0.05): w = k. g. d Therefore, the relation to proportionally scale wave period (T = 2π/ω) can be expressed as: Page 9 of 17

10 T!" T!" = d!" d!" So, re-estimated wave period (for 10 ft) can be found as: 16.3 W!!" = W! = 6.67 s 10.3 However, since the wind fetch in the current reservoir study is not the same as the one mentioned in [1], the wave height and time period should be re-estimated based on the wind fetch distance. For this purpose, two-dimensional wave equations and wave characteristics are needed to scale the height and period. The effective fetch, simple fetch, and spectral contribution methods allow relating the wave height and period to fetch and wind speed. Thus, the commonly used Hasselmann equations derived from the JONSWAP experiment, are employed here: W! = U X g W! = 2π 3.5! X. U g Where: f = wave frequency, U = wind speed, X = wind fetch, and g = 9.8 [m/s2]. The wave parameters can be scaled with respect to the original wave parameters calculated and presented in [1]: Adjusted Wave Height: W! = W!!" Fetch!"# Fetch!"#$ = 3.02 ft Adjusted Wave Period:! Fetch!"# W! = W!!" = 7.18 s Fetch!"#$ Page 10 of 17

11 Estimation of the levee height Still Water Depth: D!" = R!"#$! + WSI = 10.3 ft Structure Slope Angle: α = atan Slope = deg Method 1: Regular Wave Runup Height: Runup1 = 2.3 ft!.! s tan α. W! W! = 9.57 ft Method 2: Relative Wave Height: H! = W! D!" = Employing Momentum Flux Method Condition: Check2 = if(h! 0.8, "OK, "NG") Therefore, Momentum Flux Method is expressed as follows: Empirical Coefficient (M): M!"#$$ = tangh H_h!.!! = Empirical Coefficient (N): N!"#$$ = tanh 2.38H_h = Temporary Variable: X = tan M!"#$$ 2 H! + 1 Page 11 of 17

12 Wave Momentum Flux Factor: 𝑀𝐹𝐹 = 0.5 𝐻_ℎ! + 2𝐻_ℎ + 𝑁!"#$$! 𝐻 +1 2 𝑀!"#$$! 1 𝑋 + 𝑋! = Regular Wave Runup Height: 𝑅𝑢𝑛𝑢𝑝2 = 3.84 tan 𝛼. 𝐷!" 𝑀𝐹𝐹 = 8.57𝑓𝑡 Calculated Water Height: 𝑊𝑎𝑡𝑒𝑟𝐻𝑒𝑖𝑔ℎ𝑡 = 𝐷!" + 𝑀𝑎𝑥 𝑅𝑢𝑛𝑢𝑝1, 𝑅𝑢𝑛𝑢𝑝2 = 𝑓𝑡 Additional Levee Height: 𝐴𝑑𝑑!"#""!!!"#!! = 𝑊𝑎𝑡𝑒𝑟𝐻𝑒𝑖𝑔ℎ𝑡 𝐻!"#"" = 3.13 𝑓𝑡 Estimation of the earth work Figure 5 is representing the earth work section area. Figure 5: Earth Work Section Area. Initial earth work: Area 1: 𝐴1!"! = 𝐻!"#$! 𝑊!"#$! = 𝑓𝑡! Area 2: 𝐴2!"! = 𝑊!"#"" +!!"#""!"#$% 𝐻!"#"" = 1863 𝑓𝑡! Total Area of the Earth Work Cross Section: Required earth work: 𝐴!"! = 𝐴1!"! + 𝐴2!"! = 𝑓𝑡! Required levee height: Page 12 of 17

13 H!"#_!"#"" = Add!"#""!!!"#!! + H!"#""$"%&! = ft Area 1: A1!"# = H!"#$! W!"#$! = ft! Area 2: A2!"# = W!"#"" + H!"#_!"#"" Slope Total Area of the Earth Work Cross Section: H!"#_!"#"" = ft! A!"# = A1!"# + A2!"# = ft! Earthwork increase ratio: Embankment cross section area increase Ratio = A!"# A!"! = Cost estimates of the Reservoir The construction cost estimates for the EAA CERP Project were done using cost data found on RS Means Heavy Construction Cost Data 2016 [7], cost models, and analogous estimating. The major activities included in the cost estimates were: construction of permanent berms, construction of slurry wall, demolition and relocation of railroad tracks, construction of pump stations, and engineering/design. Earthwork Cost Estimates The quantities for earthwork were based on the parameters provided in the conceptual design presented in this document. The unit costs for earthwork relied on RS Means Heavy Construction Cost Data Cutoff Wall The cutoff wall around the perimeter of the reservoir was assumed to be 20 feet deep. The unit costs for the cutoff wall estimate relied on RS Means Heavy Construction Cost Data Pump Station Cost Estimates Pump station costs were estimated by following a procedure used in a conceptual cost estimate for a project in the everglades prepared by Burns & McDonnell Engineering Company. In 2009, a contract for pump stations G-434 and G-436 was awarded for a cost of $49.7 million. The combined capacity of these two pump stations is 2,720 cfs [8]. The cost of this project was escalated to January 2016 ($57.18 million) using an escalation factor of 15.1% obtained from the RS Mean Historical Cost Index [9]. Page 13 of 17

14 RS Means Historical Cost Index Year Month Historical Cost Index 2016 Jan Jul Jul Jul Jul Jul Jul Jul This cost was then adjusted for each one of the 6 pump stations in the proposed project by taking the capacity ratio between the proposed new pump station and the actual cost of the G-434 and G-436 project. This ratio was then raised to the 0.6 power to account for economies of scale. Engineering & Design Engineering/Design & Consulting fees were estimated as 10% of construction costs. Contingency A contingency of 20% of the total project cost was used. This contingency includes unforeseen costs and uncertainty in predicting actual construction costs due to changes in the underlying assumptions of the estimate. Contractor s Costs All construction work was assumed to be subcontracted by a general contractor and a value of 10% was used for the general contractor overhead and profit. Additionally, main office expenses were estimated as 3.9% of the project s cost. Equipment Cost and Labor Rates Equipment and labor costs for the reservoir construction activities were derived from RS Means. For the pump stations, equipment costs were assumed to be 50% of the total cost (not including contractor s overhead and profit), and labor costs where assumed to be 25% of total costs. Land The lands were the reservoir would be located, would have to be purchased. The combined area for both cells of the Project was assumed to be approximately 63,060 Acres. Due to the lack of comparable land purchases in the area of the Project, the cost of the land was assumed to be $8,086 per acre. In 2013, the South Florida Water Management District had the option of purchasing land in the EAA area for $7,400 per acre [10]. For the purpose of this cost estimate, the $7,400 per acre cost was assumed to be market value, and was increased by 3% per year. Page 14 of 17

15 Other Minor Costs Lump sum values were used for the cost estimates for testing, temporary utilities, control structures and instrumentation. These items combined were estimated to account for only 2%-4% of construction costs for the project; therefore they were not detailed any further. Total Cost After accounting for construction, supervision, engineering/design, and a 20% contingency, the conceptual cost estimate for option #1 was determined to be $2.4 Billion. Page 15 of 17