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DR1101-SY110620Page 1 of 1 Ken Griffin -North Lake From: John Rutledge <JLR9freese.com> To: Ken Griffin <kgriffingci. copp ell. tx. us> Date: 6/20/20114:47 PM Subject: North Lake Attachments: Preliminary Design Memo.pdf Ken, Attached is a draft of our report. I'd like to set up a time later this week or early next week for me to come out to your office to go over the findings. I'll call tomorrow. Were you able to locate a contact at Luminant from the agreement? Thanks JLR John L. Rutledge, P.E. Freese and Nichols, Inc. 4055 International Plaza St 200 Fort Worth, TX 76109 817 -735 -7284 jlr @freese.com kwin Q�Mq !IF Please consider the environment before printing this message. This electronic mail message is intended exclusively for the individual or entity to which it is addressed. This message, together with any attachment, may contain the sender's organization's confidential and privileged information. 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Thank you for your cooperation. file: //C: \Documents and Settings \lhenderson \Local Settings \Temp \XPgrpwise \4DFF798C... 6/21/2011 l North Lake Dam Spillway Modification City of Coppell Prepared by: FREESE AND NICHOLS, INC. 4055 International Plaza, Suite 200 Fort Worth, Texas 76109 817 - 735 -7300 CPL11192 Le North Lake Dam Spillway Modification City of Coppell Prepared by: THIS DOCUMENT IS RELEASED FOR THE PURPOSE OF INTERIM REVIEW UNDER THE AUTHORITY OF JOHN L. RUTLEDGE, P.E., TEXAS NO. 65045 ON JUNE 13, 2011. IT IS NOT TO BE USED FOR CONSTRUCTION, BIDDING OR PERMIT PURPOSES. FREESE AND NICHOLS, INC. TEXAS REGISTERED ENGINEERING FIRM F- 2144 FREESE AND NICHOLS, INC. 4055 International Plaza, Suite 200 Fort Worth, Texas 76109 817 - 735 -7300 CPL11192 North Lake Dam Spillway Modification City of Coppell O n ir ICHOLS TABLE OF CONTENTS 1.0 Introduction ................................................................................................................... ..............................1 1 .1 North Lake Dam .................................................................................................... ..............................1 2.0 Hydrologic Model Development ........................................................................... ............................... 3 2.1 Hydrologic Parameters ..................................................................................... ............................... 3 2.2 Elevation - Storage Data ..................................................................................... ............................... 6 2.3 Discharge Rating Curves ................................................................................... ............................... 7 2.4 Frequency Model Results ................................................................................. ............................... 9 2.5 PMF Model Results .............................................................................................. .............................10 3.0 Modification Alternatives ........................................................................................ .............................12 3 .1 Alternative 1 .......................................................................................................... .............................12 3 .2 Alternative 2 .......................................................................................................... .............................13 3 .3 Alternative 3 .......................................................................................................... .............................14 3 .4 Geotechnical Review .......................................................................................... .............................17 4.0 Environmental Permitting Review ...................................................................... .............................18 4.1 Permanently Lowering the Normal Pool Elevation .............................. .............................18 4.2 Activities Within the New Jurisdictional Pool Area .............................. .............................19 4.3 Activities Not Within the New Jurisdictional Pool Area ..................... .............................19 4.4 Mitigation ................................................................................................................ .............................19 4.5 Currently Functioning Spillway .................................................................... .............................20 4.6 Conclusions ............................................................................................................ .............................20 4.7 Recommendations .............................................................................................. .............................20 5.0 Summary and Conclusions ..................................................................................... .............................22 June 2011 North Lake Dam Spillway Modification City of Coppell LIST OF TABLES nRCHOLS Table 1 - Curve Number Calculation ................................................................................ ............................... 6 Table2 - Basin Parameters .................................................................................................. ............................... 6 Table3 - Elevation - Storage Data ....................................................................................... ............................... 7 Table4 - Discharge Rating Curve ........................................................................................ ..............................9 Table 5 - Frequency Precipitation Depths .................................................................. ............................... 10 Table 6 - Frequency Model Results ................................................................................. ............................... 10 Table 7 - HMR -52 Point Rainfall Depths ...................................................................... ............................... 11 Table - PMF Model Results ............................................................................................ ............................... 11 LIST OF FIGURES Figure1 - Location Map ......................................................................................................... ............................... 2 Figure2 - Drainage Basin Map ............................................................................................. ..............................4 Figure3 - Land Cover Data .................................................................................................... ..............................5 Figure 4 - Plan View of Alternative 3 ............................................................................ ............................... 15 Figure 5 - Cross Section View of Alternative 3 .......................................................... ............................... 16 APPENDICES Appendix A - References Appendix B - Hydrologic Parameters Appendix C - Discharge Rating Curve Calculations Appendix D - Opinion of Probable Construction Costs June 2011 ii North Lake Dam Spillway Modification City of Coppell 1.0 INTRODUCTION Irmill'AICHOLS In March of 2011, Freese and Nichols, Inc., (FNI) was retained by the City of Coppell, Texas, to provide design alternatives for the lowering of the conservation pool of North Lake, which is owned by the City of Coppell and located between the cities of Coppell and Irving. The current conservation pool elevation is 510.0 ft -msl. The City desires to lower this elevation according to one of two proposed plans — the first to lower the conservation pool by 20 feet to elevation 490.0 ft -msl and the second to lower it by 30 feet to elevation 480.0 ft -msl. This report summarizes the results of the hydrologic analysis, geotechnical analysis, and the review of environmental permitting issues, and presents three preliminary design alternatives. 1.1 NORTH LAKE DAM North Lake Dam, which forms North Lake, is currently owned and operated by TXU Generation Company, L.P. The reservoir once served as a cooling pond for a steam electric generating plant. However, the dam is now owned by the City of Coppell, and proposed development around the lake has called for the lowering of the conservation pool elevation. North Lake Dam was authorized by the State of Texas, Permit No. 1864, on April 23, 1957. North Lake Dam, completed in August 1957, is located on the South Fork of Grapevine Creek in the Trinity River Basin in northwestern Dallas County. It is situated on the southeast side of the City of Coppell between Interstate 635 and East Belt Line Road. The general location of the dam and reservoir is shown in Figure 1. June 2011 1 t 7, 3e504 ACwnc - Fox Ave L f tl: � B el Ire Blvd E Rnnett din (D r L CL R3 a Flower G� � —�! %)d Rd > 77 e +, 499 % �'11f Grove Rd 300 ' ,/ Spinks Rd QD Bus tll Lakeside 121 3 - ........... .... ,.....,_.. ��.. r��t rtal P�wy it ,C Rockledge � 4w era _ Park 121 P oppell C to E Bethel steal E BL Line Rd — E melt lLi - Cam N orth Q La ke ne a� E �� eel 4r hnrood Pk p e _ -J North I i r 0 Lake 0 � Park a � � a Fa (3 c` y Vie Olt 11 4 ` c' cn r �. t Tr i z w . N_s- c s - Spur Verizot4 3448 FYI Airport 1�, - s Dallas - Fort Worth �� w est N Interna rWt .. +� - t3 .Y Rnl ey Rd tf,$ spur m A, !-- rgari sx W R�ochelbe Rd �rthgate Dr 462 ,rr > =N PROJECT NO. CPL11192 0 0.75 1.5 3 N 9LE NAME RAM DESIGNIFIGURES1 Miles FIGURE Figure l- Lo.,ion Ma,_, � &FREESE DATUM& COORDINATESYSTEM ° NICNOLS JAC63 STATEPLANETE NORTH CEOTRAL(R] 4055 '11"'aT.0. P_— S,k,200 NORTH LAKE SPILLWAY MODIFICATION .� DATE CREATED F,H VV,T TX 76'09 -4695 JUNE 2011 Il', Y -/35 -/:100 'REPARED BY LOCATION MAP JPM North Lake Dam Spillway Modification City of Coppell 2.0 HYDROLOGIC MODEL DEVELOPMENT FREESE Ir M INNICHOLS The hydrologic model for North Lake Dam was created in HEC -HMS and consisted of two total drainage basins, as shown in Figure 2. The total drainage area modeled is approximately 2.61 square miles, or 1,670 acres. One basin represents the area that drains to the lake, while the other basin represents the surface of the lake itself. The overall basin was delineated from two -foot contours from the 2001 NCTCOG dataset. Because the conservation pool will be lowered from the existing level, the drainage basin representing the lake surface was approximated at elevation 490.0 ft -msl from the 2008 volumetric survey of the lake.' While the size and shape of the lake surface area may change with re- grading and development, this basin is assumed to represent an appropriate approximation. The same basin was applied for the option that lowers the conservation pool elevation to 480.0 ft -msl. A finalized hydrologic model will be developed in the final design of the spillway modification. 2.1 HYDROLOGIC PARAMETERS The HEC -HMS model incorporates the NRCS Curve Number and Unit Hydrograph methods for each basin. In this model, the curve numbers were based on hydrologic soil classifications and land cover. The soils dataset was obtained from the NRCS Soil Survey Geographic Database (SSURGO), and land use classification was determined from a combination of the 2005 NCTCOG Land Use Data' and the proposed master plan for future development . Spatial information about the land use classifications is presented in Figure 3. Table 1 provides the matrix used in determining the curve number for each basin. All soils in the basin are in Hydrologic Soil Group D. The curve numbers shown in Table 1 represent both Antecedent Moisture Condition (AMC) II, which is incorporated in the model for frequency storms, such as the 100 -year event, and AMC III, which is used to simulate a worst -case scenario with the ground full saturated for the Probable Maximum Flood (PMF) events. June 2011 3 7 '- l 1 s b =N PROJECT NO. CPL11192 0 1,000 2.000 4.000 N 9LE NAME H1WR_DESIGNtFIGURES\ Feet FIGURE Figure 2- Basminlxd FREESE DATUM & COORDINATE SYSTEM �� ° N OMS JAM3 STATEPUWETE NORTH=RAL(R] 4055 International Plaza. S,,W 200 NORTH LAKE SPILLWAY MODIFICATION 2 DATE CREATED Fort Worth. TX 76109-4895 JUNE 2011 817 -735 -7300 'REPARED BY JPM DRAINAGE BASIN MAP North Lake Dam Spillway Modification City of Coppell Table 1 - Curve Number Calculation FREESE Ir m ill'AICHOLS Land Use Code Classification Description Curve Number (AMC II) Curve Number (AMC III) 111 Single Family 87 94 112 Multi - Family 92 96 121 Office 95 98 122 Retail 95 98 123 Institutional 93 97 131 Industrial 93 97 142 Roadway 98 99 171 Parks /Recreation 80 90 300 Vacant 89 95 500 Water 100 100 The only input into HEC -HMS for the NRCS Dimensionless Unit Hydrograph is a lag time, which is calculated based on basin conditions, such as hydraulic length and average slope, according to the NRCS TR -55 Method. The lag time for North Lake was computed by FNI during a previous study for the development of an Emergency Action Plan (EAP). Table 2 provides a summary of the hydrologic parameters for the basin representing the area outside of the lake surface. Detailed calculations for the hydrologic parameters are provided in Appendix B. The basin representing the lake surface was given no runoff loss or hydrograph transformation parameters, so as to reflect the instantaneous nature of the direct runoff. Table 2 — Basin Parameters 2.2 ELEVATION- STORAGE DATA Elevation- storage data for the reservoir was approximated with the one -foot contours generated from the 2008 volumetric survey to calculate the available storage in the reservoir. The elevation- storage relationship was used in the hydrologic model for routing both the frequency storm events and the PMF and is shown in Table 3. June 2011 6 Curve Curve Area Lag Time Basin z (mi) (min) Number Number (AMC II) (AMC III) Basin 2.02 18.6 90.5 95.6 Lake 0.59 - -- - -- - -- 2.2 ELEVATION- STORAGE DATA Elevation- storage data for the reservoir was approximated with the one -foot contours generated from the 2008 volumetric survey to calculate the available storage in the reservoir. The elevation- storage relationship was used in the hydrologic model for routing both the frequency storm events and the PMF and is shown in Table 3. June 2011 6 North Lake Dam Spillway Modification City of Coppell Table 3 - Elevation- Storage Data Elevation (ft -msl) Storage (acre -ft) 450 0 460 95 470 520 480 1,937 482 2,391 484 2,908 486 3,491 488 4,142 490 4,862 492 5,656 494 6,525 496 7,477 498 8,511 500 9,631 502 10,842 504 12,148 506 13,555 508 15,091 510 16,718 512 18,386 514 20,109 516 21,895 2.3 DISCHARGE RATING CURVES Ir w ill'AICHOLS North Lake Dam currently has a single spillway structure located in the right abutment of the embankment on the northeast corner of the dam. Information regarding the dimensions and elevations of the spillway was taken from original construction drawings. The existing spillway has a crest elevation of 510 ft -msl with a total length of 200 feet. The spillway approach is lined with rock riprap and the crest is an asphalt roadway. The spillway discharges through a concrete -lined chute along the downstream toe of the dam into a stilling basin then down to the South Fork of Grapevine Creek. Three modification alternatives were analyzed for this study and will be discussed in greater detail later in this report. Each of these alternatives proposes removing the existing June 2011 7 North Lake Dam Spillway Modification City of Coppell FREESE overflow spillway structure and replacing it with some sort of riser and conduit system. A portion of the existing concrete chute, along with the stilling basin, will remain in each proposed alternative. Alternatives 1 and 2 have the normal pool elevation at 490.0 ft -msl, and Alternative 3 has the normal pool elevation at 480.0 ft -msl. Alternative 1 consists of a riser with a 100 -ft weir length in a labyrinth configuration. This was selected in order to keep the 100 -year flood to less than a 2 -ft rise, as preferred by the developer. This is discussed in more detail in the next section of this report. The conduit is an 8 -ft reinforced concrete box. Alternative 2 consists of a square riser with an effective weir length of 30 feet. The conduit is a 5 -ft reinforced concrete box. Alternative 3 consists of the same riser and conduit combination as Alternative 2. No practical configuration was found to keep the 100 -year flood to less than a 2 -ft rise with the starting water surface elevation at a normal pool of 480 ft -msl. The discharge rating curves were calculated using both weir and pressure flow equations and are shown in Table 4, with detailed calculations presented in Appendix C. June 2011 8 North Lake Dam Spillway Modification City of Coppell Table 4 - Discharge Rating Curve Alternative 1 Elevation (ft -msl) Discharge (cfs) 490.0 0 490.5 116 491.0 329 491.5 603 492.0 926 492.5 1,291 493.0 1,553 493.5 1,574 494.0 1,595 495.0 1,635 496.0 1,674 497.0 1,713 498.0 1,751 499.0 1,788 500.0 1,824 501.0 1,859 502.0 1,894 503.0 1,928 504.0 1,962 505.0 1,995 510.0 2,152 515.0 2,299 Alternative 2 Elevation (ft -msl) Discharge (cfs) 490.0 0 490.5 34 491.0 95 491.5 171 492.0 258 492.5 352 493.0 453 493.5 551 494.0 558 495.0 571 496.0 583 497.0 596 498.0 608 499.0 620 500.0 632 501.0 643 502.0 655 503.0 666 504.0 677 505.0 687 510.0 739 515.0 787 Irmill'AICHOLS Alternative 3 Elevation (ft -msl) Discharge (cfs) 480.0 0 480.5 34 481.0 95 481.5 171 482.0 258 482.5 352 483.0 453 483.5 516 484.0 522 485.0 534 486.0 546 487.0 557 488.0 569 489.0 580 490.0 591 491.0 602 492.0 612 493.0 623 494.0 633 495.0 643 500.0 691 515.0 819 2.4 FREQUENCY MODEL RESULTS The 100 -year frequency - or 1% annual chance - storm event was analyzed for each of the North Lake Dam spillway modification alternatives. The hydrologic model described in the preceding sections was implemented in analyzing this event. Curve numbers were set to AMC II, and initial abstractions were calculated automatically by HEC -HMS. These assumptions represent normal conditions, as would be expected prior to a storm event of this nature. The precipitation data was obtained from the Integrated Stormwater Management (iSWM) Manual developed by NCTCOG for the north - central Texas region. These values are presented in Table 5. Each storm event was assumed to have a duration of 24 hours. June 2011 9 North Lake Dam Spillway Modification City of Coppell FREESE Ir m ill'AICHOLS Table 5 - Frequency Precipitation Depths Frequency Precipitation (in) (yrs) 5 min 15 min 60 min 2 hr 3 hr 6 hr 12 hr 24hr 1 0.44 0.85 1.40 1.66 1.83 2.10 2.40 2.64 2 0.50 1.00 1.73 2.08 2.28 2.64 3.12 3.60 5 0.60 1.24 2.24 2.76 3.06 3.60 4.20 4.80 10 0.66 1.40 2.60 3.22 3.60 4.26 4.92 5.76 25 0.76 1.63 3.07 3.84 4.32 5.16 6.12 7.20 50 0.84 1.81 3.45 4.36 4.89 5.88 6.96 8.40 100 0.93 2.00 3.86 4.90 5.55 6.72 8.04 9.60 500 - -- 3.00 4.86 6.12 6.99 8.76 11.04 13.68 These precipitation depths serve as input data into the hydrologic model, and were routed through the model as described previously. The results from the 100 -year storm event runs are shown for each alternative in Table 6. Table 6 - Frequency Model Results As noted previously, the size for Alternative 1 was chosen to limit the 100 -year rise to 2 feet. Such an alternative was not feasible at a normal pool elevation of 480 ft -msl. 2.5 PMF MODEL RESULTS The Probable Maximum Flood (PMF) is defined as the greatest flood to be expected, and the Probable Maximum Precipitation (PMP) is theoretically the greatest depth of rainfall for a given duration that is physically possible over a given size storm area at a particular geographic location. Generally, the rainfall depth is calculated for the ten square miles of the watershed which receive the highest intensity rainfall. Hydrometeorological Report No. 52 (HMR -52), developed by the U.S. Army Corps of Engineers, was used to determine the rainfall for each basin. PMP estimates were taken from June 2011 10 Normal Peak Peak Peak Modification pool Elevation Inflow Outflow Alternative (ft -msl) (ft -msl) (cfs) (cfs) Alt 1 490 491.97 7,856 904 Alt 2 490 492.34 7,856 323 Alt 3 480 483.58 7,856 517 As noted previously, the size for Alternative 1 was chosen to limit the 100 -year rise to 2 feet. Such an alternative was not feasible at a normal pool elevation of 480 ft -msl. 2.5 PMF MODEL RESULTS The Probable Maximum Flood (PMF) is defined as the greatest flood to be expected, and the Probable Maximum Precipitation (PMP) is theoretically the greatest depth of rainfall for a given duration that is physically possible over a given size storm area at a particular geographic location. Generally, the rainfall depth is calculated for the ten square miles of the watershed which receive the highest intensity rainfall. Hydrometeorological Report No. 52 (HMR -52), developed by the U.S. Army Corps of Engineers, was used to determine the rainfall for each basin. PMP estimates were taken from June 2011 10 North Lake Dam Spillway Modification City of Coppell IrMINNICHOLS Hydrometeorological Report No. 51 and distributed according to HMR -52 to obtain average rainfall depths over the various drainage areas. HMR -52 calculates rainfall depths for storm durations ranging from five minutes to seventy -two hours. Table 7 lists the point rainfall depths calculated by HMR -52 for storm durations from one hour to 72 hours. Because the total drainage area is less than ten square miles, the same rainfall depths were applied over the entire drainage area. Additionally, the total rainfall depth was distributed according to the temporal distribution described by the TCEQ Hydrologic and Hydraulic Guidelines for Dams in Texas. Table 7 - HMR -52 Point Rainfall Depths Storm Duration (hr) Depth (in) 1 16.63 2 20.72 3 23.92 6 29.95 12 36.05 24 41.26 48 46.11 72 48.87 The PMF was modeled for each modification alternative, as described previously, with flood routing started at both normal pool elevations. According to TCEQ regulation s, the North Lake Dam is classified as an intermediate -size, high- hazard structure. As such, North Lake Dam is required to pass 100% of the PMF to be in compliance with the TCEQ regulations. The critical PMF duration for Alternative 1 was 24 hours, while the critical duration for Alternatives 2 and 3 was 48 hours. Table 8 contains the results of these PMF model runs. Table 8 - PMF Model Results June 2011 11 Normal Critical Peak Peak Peak Modification pool Duration Elevation Inflow Outflow Alternative (ft -msl) (hrs) (ft -msl) (cfs) (cfs) Alt 1 490 24 497.93 6,955 1,748 Alt 2 1 490 1 48 1 499.96 1 4,129 1 632 Alt 3 1 480 1 48 1 494.25 1 4,129 1 636 June 2011 11 North Lake Dam Spillway Modification City of Coppell 3.0 MODIFICATION ALTERNATIVES FREESE Ir w ill'AICHOLS Alternatives were developed for two different normal pool elevations — 480 ft -msl and 490 ft -msl. A total of three modification alternatives were analyzed. Alternatives 1 and 2 have the normal pool elevation at 490.0 ft -msl, and Alternative 3 has the normal pool elevation at 480.0 ft -msl. Each of these alternatives proposes removing the existing overflow spillway structure and replacing it with a riser and conduit system. All three alternatives utilize the same proposed location of the riser structure and proposed alignment of the conduit. Figure 4 shows a plan view of Alternative 3 as an example of the proposed location and alignment. Figure 5 shows a cross section view of the spillway for Alternative 3, including the excavated approach channel. Alternative 3 was selected as the example because it represents the most significant amount of excavation due to the lower normal pool elevation. A portion of the existing concrete chute will remain in place for each proposed alternative. The conduit will run from the riser through the right abutment of the dam, where it will bend to the alignment of the existing chute until the flowline of the conduit daylights into the chute. The conduit will have a headwall, and discharges will flow through the existing chute to the existing stilling basin, which will also remain. 3.1 ALTERNATIVE 1 Alternative 1 consists of a concrete riser with a 100 -ft weir length in a labyrinth configuration with a crest elevation of 490.0 ft -msl. This was selected in order to keep the 100 - year flood to less than a 2 -ft rise, as preferred by the developer. The conduit is set to be an 8 -ft by 8 -ft reinforced concrete box, so as to maintain proper hydraulic behavior during the 100 - year flood event. The riser will be controlled by weir flow up to elevation 492.8 ft -msl, at which point the conduit will flow full and be controlled by pressure flow. June 2011 12 North Lake Dam Spillway Modification City of Coppell CHOLS An approach channel will be excavated to elevation 483.0 ft -msl with a 2 -ft layer of rock riprap on the bottom, side slopes, and around the riser structure. The width of the approach channel will be 44 feet with 3:1 side slopes. During construction, a portion of the existing ground surface will remain in place to act as a coffer dam to provide a dry working area for the construction of the riser and conduit. This will then be excavated and lined with riprap as mentioned previously. The estimated construction cost of Alternative 1 is $2,429,200. A detailed Opinion of Probable Construction Costs for each alternative is given in Appendix D. 3.2 ALTERNATIVE 2 Alternative 2 consists of a square concrete riser with 10 -ft by 10 -ft interior dimensions and 12 -inch thick walls. Because of the need for backfill around the conduit, the effective weir length is 30 feet. The crest of this riser is also at elevation 490.0 ft -msl. This riser was selected as a simpler alternative to the labyrinth weir design of Alternative 1, and the 100 -year flood rise is only 2.34 feet. The conduit is a 5 -ft by 5 -ft reinforced concrete box. The riser will be controlled by weir flow up to elevation 493.5 ft -msl, at which point the conduit will flow full and be controlled by pressure flow. An approach channel will be excavated to elevation 483.0 ft -msl with a 2 -ft layer of rock riprap on the bottom, side slopes, and around the riser structure. The width of the approach channel will be 44 feet with 3:1 side slopes. During construction, a portion of the existing ground surface will remain in place to act as a coffer dam to provide a dry working area for the construction of the riser and conduit. This will then be excavated and lined with riprap as mentioned previously. The estimated construction cost of Alternative 2 is $2,170,300. A detailed Opinion of Probable Construction Costs for each alternative is given in Appendix D. June 2011 13 North Lake Dam Spillway Modification City of Coppell 3.3 ALTERNATIVE 3 n CHOLS Alternative 3 consists of the same riser and conduit combination as Alternative 2. The riser has interior dimensions of 10 -ft by 10 -ft with a crest elevation of 480.0 ft -msl. The conduit is a 5 -ft by 5 -ft reinforced concrete box. The riser will be controlled by weir flow up to elevation 483.3 ft -msl, at which point the conduit will flow full and be controlled by pressure flow. No practical configuration was found to keep the 100 -year flood to less than a 2 -ft rise with the starting water surface elevation at a normal pool of 480 ft -msl. The weir length necessary to maintain this little rise is not feasible for a riser and conduit system. The 100 -year flood rise for Alternative 3 is 3.58 feet. An approach channel will be excavated to elevation 473.0 ft -msl with a 2 -ft layer of rock riprap on the bottom, side slopes, and around the riser structure. The width of the approach channel will be 44 feet with 3:1 side slopes. During construction, a portion of the existing ground surface will remain in place to act as a coffer dam to provide a dry working area for the construction of the riser and conduit. This will then be excavated and lined with riprap as mentioned previously. The estimated construction cost of Alternative 3 is $3,143,200. A detailed Opinion of Probable Construction Costs for each alternative is given in Appendix D. As mentioned previously, Figures 4 and 5 show the plan view and cross section view, respectively, of Alternative 3. June 2011 14 Fo Il v 1 r Ov MA �� 714 0 H w w o z w J C) Cn Fo Il v 1 r Ov MA �� 714 0 North Lake Dam Spillway Modification City of Coppell 3.4 GEOTECHNICAL REVIEW FREESE Ir m ill'AICHOLS A preliminary review of the geotechnical stability of the embankment demonstrated that the lake could be drawn down from its current levels to approximately elevation 488.0 ft- msl without any concerns for the stability of the upstream face. Reductions below that will need some delay, but would be expected to be within the timeframe of construction process and can be handled by the contractor. Precise limits will depend on the final selected configuration and the additional geotechnical exploration and laboratory testing that will be needed during the final design. June 2011 17 North Lake Dam Spillway Modification City of Coppell 4.0 ENVIRONMENTAL PERMITTING REVIEW FREESE North Lake currently has a surface area of approximately 800 acres at an elevation of 510 feet msl and a maximum depth of about 40 feet. Grapevine Creek is a tributary of the Elm Fork Trinity River, a Relatively Permanent Waterbody (RPW). Therefore, the South Fork of Grapevine Creek, a tributary of Grapevine Creek, is a jurisdictional water of the U.S. The City of Coppell (City) has purchased the lake and the surrounding area and has requested that Freese and Nichols provide a permitting evaluation discussing the permanent lowering of the reservoir's normal pool elevation to either 480 feet msl or 490 feet msl in order to accommodate a planned residential development. 4.1 PERMANENTLY LOWERING THE NORMAL POOL ELEVATION According to David Madden, Project Manager for the U.S. Army Corps of Engineers ( USACE), any activity involving the placement of fill material in a water of the U.S. would require a Section 404 (Clean Water Act) Permit. For example, construction of a new spillway structure within the existing normal pool (510 feet msl) area would require a Section 404 Permit. However, Mr. Madden also stated that if a jurisdictional reservoir were to be modified to permanently lower the normal pool elevation without the placement of fill within the existing normal pool area, no Section 404 permit would be required. Regardless of how the normal pool elevation is permanently lowered, a new jurisdictional limit would be established when the newly exposed land surface completely dries out, establishing a new normal pool elevation, shoreline, and jurisdictional limit, based on the elevation of the new permanent spillway. If the permanent placement of fill within the current normal pool area were necessary to establish the new pool elevation, such as in the construction of a new spillway and /or placement of rock riprap, there are two options available for pursuing USACE authorization for the project: a standard individual permit (IP) or a modified IP (Letter of Permission 1 (LOP -1)). June 2011 18 North Lake Dam Spillway Modification City of Coppell NRCHOLS An IP application process would involve the submittal of detailed project plans and a mitigation plan for adverse impacts to waters of the U.S., as well as a public review and comment period and consultation with state and federal resource agencies. The application procedure with LOP -1 is similar to that of submitting an IP, except that the USACE would not require public notification. They would still afford the resource agencies an opportunity to review and comment on the project. The USACE would have the option of rejecting the LOP -1 procedure and require an IP submittal instead if they deemed that the project was not in the public's best interest. 4.2 ACTIVITIES WITHIN THE NEW JURISDICTIONAL POOL AREA Any work performed within the new normal pool area involving fill activities would require a permit, most likely an IP, from the USACE. Activities can be conducted if performed in such a way that avoids more than incidental fallback of dredged material. Discharge of more than incidental fallback is considered a fill activity by the USACE. For example, excavation with a back hoe bucket may be considered to have only incidental fallback, but excavation with an earthmover or bulldozer could be considered by the USACE to involve more than incidental fallback (i.e., involves the placement of fill) and therefore would require a permit. 4.3 ACTIVITIES NOT WITHIN THE NEW JURISDICTIONAL POOL AREA Construction activities outside the new normal pool area of the reservoir, including the placement of fill material, would not require a Section 404 Permit once the area outside the new normal pool area has completely dried out. 4.4 MITIGATION Permitted activities causing permanent impacts to jurisdictional waters of the U.S., such as the placement of fill material within the existing or new normal pool areas, would require compensatory mitigation. In this scenario, the purchase of mitigation bank credits may be a practicable alternative to permittee responsible mitigation. Open water credits at the Trinity River Mitigation Bank cost approximately $50,000 to $100,000 per acre of impact, depending June 2011 19 North Lake Dam Spillway Modification City of Coppell IrMINNICHOLS on the quality of the water resource impacted (i.e., low or medium versus high quality open water habitat). 4.5 CURRENTLY FUNCTIONING SPILLWAY A 42 -inch diameter pipeline that originally served to transport water from the Elm Fork Trinity River (Elm Fork) to North Lake for use in the generation of electric power has been functioning as a spillway since early 2010. The pipeline invert elevation is 502.25 feet msl, and any overflow would flow directly to the Elm Fork. It may be possible to construct the proposed permanent spillway on land above this elevation that has been de- watered by the 42 -inch pipeline. 4.6 CONCLUSIONS The construction of a new spillway structure within the footprint of the existing normal pool area (510 feet msl or below) would require a Section 404 permit. Once the normal pool elevation has been permanently lowered, construction above the new normal pool elevation /jurisdictional limits can occur when the newly exposed land has completely dried out. If the USACE agrees that the normal pool elevation is now 502.25 feet msl, based on the invert elevation of the 42 -inch diameter pipeline that apparently now controls the water surface elevation, then the construction of the proposed spillway may not impact waters of the U.S. and may not require a Section 404 permit. 4.7 RECOMMENDATIONS A Pre - Application meeting with the Fort Worth District USACE to discuss the method described above for constructing a new spillway within the existing normal pool area (510 feet msl or below), or above the existing "functional" normal pool area elevation (502.25 feet msl), is recommended. Construction activities within the proposed new normal pool area by the developer would require a Section 404 permit. It may be in the City's best interest to have the developer pursue their own USACE permit for such activities. Were the City to obtain a permit for the June 2011 20 North Lake Dam Spillway Modification City of Coppell FREESE developer's construction activities, and then the developer violated the terms of the permit, the City could be held liable. June 2011 21 North Lake Dam Spillway Modification City of Coppell 5.0 SUMMARY AND CONCLUSIONS Irmill'AICHOLS The proposed design alternatives for the North Lake spillway, as described above, provide three viable options for achieving the goal of lowering the conservation pool of the lake. Each of the three alternatives has been modeled according to State criteria using the best available information. The Opinion of Probable Construction Costs estimates that the cost for Alternative 1 would be $2,429,200, the cost for Alternative 2 would be $2,170,300, and the cost for Alternative 3 would be $3,143,200. A review of environmental permitting issues concluded that a Section 404 permit may be required for the construction of the new spillway because it would be within the existing normal pool area. However, the normal pool elevation may be deemed to be 502.25 ft -msl, rather than 510 ft -msl, based on the flowline of the 42 -inch pipe that is now open and controls the water surface elevation. A meeting with the Fort Worth District USACE will be necessary to make the final determination. In either case, once the lake has been lowered to the new normal pool elevation and the land has fully dried out, any construction above the new normal pool level will not require a permit. Construction below the new normal pool level will require a Section 404 permit, and it is recommended that this be obtained by the developer, rather than the City. June 2011 22 North Lake Dam Spillway Modification City of Coppell Appendix A References n CHOLS June 2011 North Lake Dam Spillway Modification City of Coppell References Irmill'AICHOLS 1. U.S. Army Corps of Engineers, Hydrologic Engineering Center: Hydrologic Modeling System HEC -HMS - User's Manual Version 3.5, Davis, California, August 2010. 2. North Central Texas Council of Governments (NCTCOG): 2001 Digital Elevation Contours. < http:// gis .nctcog.org /contours_2001.asp >. 3. Lina T. Ramey and Associates, Inc. Ba thyme tric Survey of North Lake. [computer map]. Dallas, Texas, September 2008. 4. "Soil Data Mart." NRCS Soil Survey Geographic (SSURGO) Database. < http : / /soildatamart.nres.usda.gov >. 5. North Central Texas Council of Governments (NCTCOG): 2005 Land Use G/S Data. <http: / /www.nctcog.org /ris /demographics /landuse.asp >. 6. Billingsley Company. Cypress Waters Draft Masterplan, September 22, 2009. 7. Freese and Nichols, Inc. North Lake Dam Emergency Action Plan. Fort Worth, Texas, March 2005. 8. North Central Texas Council of Governments (NCTCOG): integrated Stormwater Management (iSWM) Technical Manual, April 2010. <http: / /iswm.nctcog.org/ technical_manual.asp >. 9. U.S. Department of Commerce, National Oceanic and Atmospheric Administration and U.S. Department of the Army, Corps of Engineers: Hydrometeorological Report No. 52, Application of Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, Washington, D.C., 1982. 10. U.S. Department of Commerce, National Oceanic and Atmospheric Administration and U.S. Department of the Army, Corps of Engineers: Hydrometeorological Report No. 51, Probable Maximum Precipitation Estimates, United States East of the 105th Meridian, Washington, D.C., 1978. 11. Texas Commission on Environmental Quality (TCEQ): Hydrologic and Hydraulic Guidelines for Dams in Texas, January 2007. 12. Texas Administrative Code, Title 30, Part I, Chapter 200, Subchapter B, Rule §299.11, Effective January 2009. June 2011 North Lake Dam Spillway Modification City of Coppell Appendix B Hydrologic Parameters n CHOLS June 2011 Z I U 00 N Ol In m In Ol m Ol m Ol w Ol O 00 m 00 0 O 00 00 m O m m K v O 'T m i11 0) no' 00 Do KT O1 00 I ° oo 0 v o o m o Ln m O_ KT o a1 `- m m N m cm m Lrn ro w K }' O Lr r,,i O ++ m � Do l0 I� m w 0 m N O N m m^ F In m w m ro 7 0 00 M M Q7 i Q ri N m ^ _ m W Ln I� N ci Lo w IIl c-I N m o _° *' c a1 N ci in Ol m ci m O w - o o O 00 U Q) Lo m K M v • ru o — — a o o lf1 N U N C U a Ln •E w H a C E C E 7 - O 7 - O a) Q v) Q N f0 > J a! — > C a1 D U U O EAU ci N a) � N Q m w KT o KT in c-I w r-I in a1 p w v N o N w KT w w in - O a) fl- w I O 0 N ci c-I I m Il% m o E i 0 N o w o m In In ci m o o w D _ ci m ci m Cl. In m Qi v O O O v O O O O O O O O O o O O O O O O O O O O N a c Lu 0 o > > 0 o o v 0 Ln Lo «� i y. 0 f0 c-I ci CL N N v— U +° D- O O N V v c u Cc U) o `o N ci N N m N v w ° •— o v - c °�> N -I c i Il � ? U J �' -(� O v O ci ci ci ci m ci Ln -i ci ci ro ci 2 'n c i i ci r c i c i ci ri ci m U c Q) c w ci 0 ci N ci ci N N N m N ci m�T N ci Il 0 0 0 0 o ' J m In zz � Q U Z t z Z m m m m U U a m m m m m m m m m m m m a U o O N N O o O m O In N O N I� N F, n l0 N O w N o w w L 00 l0 In N O m N . - In '1: 00 -4 00 � . 1 U O - i O m m O N O ci 0 0 0 - i O O Ki O N I� c 0 O Z I U 00 In 0) Ln 0) m 0) m 0) o 00 Ol 00 oo 0) 0 0 n N N N 00 0) 0) 0) Ln m Ln 0) 0) Ol Ln N m Ln Ln N O Ol a) Ol Ol Ol Ol 00 C t � ci 0 ci m 06 m O ci 'O U ro m U 0 oA Z U N Il oo In In 00 00 m O m m K v O 'T m i11 0) no' 00 Do KT O1 00 I ° oo 0 v o o m o Ln m 0o KT o m `- m m N m cm m Lrn ro w K 'n m Lr r,,i O ri m � Do l0 I� m w 0 m N O N m m^ F In m w m 00 00 M M Q7 i Q ri N m ^ w m W Ln I� N ci N ci w IIl c-I N m o N Ln N ci in Ol m ci m l0 00 l0 00 N KT m K M c-I IIl o Ln •E O EAU ci m w N o w in m w KT o KT in c-I w r-I in KT m w v N o N w KT w w in Ln ci KT m w I m w KT n N ci c-I I m Il% m o i 0 N o w o o In In ci m o o w ci m ci m ci m ri In m m N i O O O O O O O O O O O O O O O O O O O O O O O N a c Lu 0 y. 0 f0 c-I ci ci N N N m N m m ci Il O O N V O O c-I c i N c i N c i N ci N N m N N N N N N -I m N N N N N N -I c i Il � ? U J ci ci ci ci ci ci m ci Ln -i ci ci ci ci ci c i i ci r c i c i ci ri ci m U N z Z m m m m m m m m m m m m m m m m m m m m m m m H Q1 7 U C t � ci 0 ci m 06 m O ci 'O U ro m U 0 oA Z U North Lake Dam Spillway Modification City of Coppell n CHOLS Appendix C Discharge Rating Curve Calculations June 2011 7 7 7 7 E E E E � O O N LfI Ol 4:1 O 4:1 Ln Ln l0 l0 I- r 00 00 m O O c-I ri 4 :1 - lfl O W 4f O M N 00 r-I N N N N N N N N N N N M M M M M M 00 O O N 00 O Ln O Ln O 6 O O c I q0 a C J c-I M Rt Ln Ln 4 :1 - M ri 00 4 :1 - m 4 :1 - 00 N Ln N m O `� O� N O N m Ln I m M I ri Ln 00 N Ln m N l0 m Ln Ol 41 U LL c-I M l 0 0) N Ln Ln Ln l0 l0 I F- r- 00 00 00 Ol Ol Ol ri N C r r r r ri ri ri ri ri ri ri ri r r r N N O } C } O z U O N - u U O U N Ln U L W L 30 N N 0) r N M Ln Ln 4 :1 - M r-I 00 4 :1 - M 4 :1 - 00 N Ln N 0) V) ,} N 4 :5 - ( .o fl 00 r i M Ln I� O) M I ri Ln 00 N Ln Ol N l0 Ol Ln Ol V) U 4 :1 - 4 :5 - 4 :5 - 4 :1 - Ln Ln Ln Ln Ln l0 l0 I r r 00 00 00 Ol Ol Ol ri N LL r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I r-I N N O_ Il Ill Q > > > 0 0 0 d d d LL u 3 N Ol Ol O Ol Ol I- (D O) N Ln Ln 4:1 N 00 Rt Ol 4:1 4:1 O O l0 Ol N l0 00 ri 4 :1 - r O Ln r l0 ri l0 ri l0 O Ln Ol 4:1 Ln Ln U r r 00 00 00 M M M O O r-I r-I N N M M��4:1 Ln I- m O W r r r r r r r r N N N N N N CV N N N N N N N L N 00 o m m w ri Ln Ln 3 VI l0 Ol m l0 O O M O M 0000 ri ri Ln l0 ri N Ln N O } U O r-I N O N O Ln O l0 M O r-I r-I L.L c-I M l0 0) ri � N N M 4:1 Ln I 00 O r-I M 4 :1 - l0 00 r- r- r-I r-I r-I r-I r-I ri N M L N U6 Ln O Ln O Ln O Ln O Ln O O O O O O O O O O O O O O +�+ ( O O c c N N M M 4 LfI l0 I-� 00 Ol O c N M 4 LfI O LfI Ol Ol Ol Ol Ol Ol Ol Ol Ol Ol M M M M O O O O O O r-I r-I 7 N 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 Ln Ln Ln Ln Ln Ln Ln Ln 7 7 7 7 E E E E � 4f 4f Ln O O O ri O M N 00 00 N ri N M O N 0 ri 0) 00 I- O M O 0) 00 O O N 00 O Ln O Ln O 6 O O c I a J J 41 a c a) c J a } C } O z O N - u U O U Ln U L W C N N . 0 -+ 4- v L -� O U Q E + to J a o> E ° ° C ° °' C _ 0 I= O W N � J U U J N O S wi LjJ Q L N ` 5 C C L • L • • L_ U U '} U N N N L U z D 0 z >� >� >� Q Q Q Il Ill Q > > > 0 0 0 d d d LL 7 7 7 7 E E E E O O O Rt 00 N N M M Rt Rt Ln Ln l0 l0 I- r- r- O r-I O f r-I r-I r-I N N N N N N N N N N N N N M M W O M N Ln Ln N ri N O Tt O ri 0) 00 I- r M O 01 00 O to N Ln O Ln O Ln O LfI O c I c I 00 a C J 0 3 N Ln ri 00 N M r-I 00 r-I M to 00 O N M Ln to I r� m r '} O M Iv Ln Ln Ln Ln Ln I- 00 m O N M Rt Ln lb I- 00 M 00 LO v r-I N M Rt Ln Ln Ln Ln Ln l0 l0 l0 to l0 to l0 l0 I- r- 0 a U } C } O z N O N - u U O U y N Ol r :t ri 00 Rt ri 00 ri M lD 00 O N M Ln l0 I M1 m I an O U O O r-I N M M Rt un Ln I� 00 Ol O N M Rt Ln l0 I 00 M 00 N W v L Ln Ln Ln Ln Ln Ln Ln Ln Ln Ln Ln Ln to to to to to to l0 to I r- d O W N � J U U J N O S wi LjJ Q L N ` 5 C C L • U 3 N N Ln 00 O M Ln to 00 m N-:t Ln Ln Ln Ln -:t M N O 00 N Ln 0 M O '} ' L Ln lb IZ Ol O ri N M Rt r� Ol ri M Ln F� Ol ri M Ln Co L V to to to to I I I I I I I w w w w w m m m m ri 0 L to O M r w M O � N r r `� O Ln I- Ln Ln Ln Ln l 0000 O N N r Il N Rt N 00 O rl U M CF) c N M Ln l0 00 ri M Ln I 00 O ri N N M I W ri r r ri ri N N N N N r L N 0 U6 Ln O Ln O Ln O Ln O Ln O O O O O O O O O O O O O O + ( CU O O c-I c-I N N M M 4 LfI l0 I-� 00 Ol O c-I N M 4 LfI O LfI 7 N Ol Rt Ol Rt Ol Rt Ol Rt Ol Rt Ol Rt Ol Rt Ol Rt Ol Rt Ol Rt M Rt M Rt M Rt M Rt O Ln O Ln O Ln O Ln O Ln O Ln r-I Ln r-I Ln 7 7 7 7 E E E E � 4 4f Ln O O O M O M N Ln Ln N ri N O Tt O ri 0) 00 I- r M O 01 00 O to N Ln O Ln O Ln O LfI O c I c I a J J a c a) c J a } C } O z O N - u U O U Ln U d N i > V) 4 ' O N O �iL O L W C N N 4-+ 4- v L 0 O U Q E + to J a o> E ° ° C ° °' C _ 0 I= O W N � J U U J N O S wi LjJ Q L N ` 5 C C L • L • • L_ U U '} U N N N L U z D 0 z >� >� >� Q Q Q Il Ill Q > > > 0 0 0 d d d LL 7 7 7 7 E E E E O O f O O Rt 00 c-I ri ri N N M M Rt Rt Rt Ln Ln l0 00 M W r-I r-I r-I N N N N N N N N N N N N N N M M O M N Ln Ln N 00 ri H O M O ri 00 I- to ri M O 01 q0 0 to N 0) O Ln O O LfI O c I c I C a O 3 N rn Ln - 1 00 N M to N to Il m O c N N M M M c m '} O M Iv Ln Ln Ln r i N M Rt Ln l0 00 m O ri N M Rt Ol r i LO v ri N M Rt Ln Ln Ln Ln Ln Ln Ln Ln Co to to to l0 l0 00 O c a) c J U a N } C } O z in O I M O r M m to N Rt to r m O r-I N N M M M r-I m O V) u F r 00 0 0 0 0 r-I N M I Ln l0 00 m O r-I N M Rt Ol r-I N V) �..� W L N N Ln Ln Ln Ln Ln Ln Ln Ln Ln Ln to to to to to to 00 d J a o> E ° ° C ° °' c _ 0 U 3 N N Ln 00 O M Ln to 00 m N-:i Ln Ln Ln Ln -:i M N O 00 N Ln N r- O '} ' L Ln lb F� Ol O r-I N M Rt r� Ol r-I M Ln F� Ol ri M Ln Co Q Q L V to to to to I I I I I I I w w w w w m m m m r'I O L Ln Ln to O O N M N r-I r-I w Il M N O Rt � N N 00 r-I O r-I rl `� U O M CF) I- N Ln M L L l 0000 r-I M Ln I 00 O ri N N M I W r r r ri ri N N N N N r L N 0 U6 Ln O Ln O Ln O Ln O Ln O O O O O O O O O O O O O O + ( CU O O c-I c-I N N M M 4 LfI l0 I-� 00 Ol O c-I N M 4 LfI O LfI 7 N 00 Ri 00 Ri 00 Ri 00 00 Ri 00 00 Ri 00 Ri 00 Ri 00 Ri 00 Ri 00 Ri 00 Ri 00 Ri Ol Rt Ol Rt M Rt M Rt M Rt M Rt O Ln r Ln 7 7 7 7 E E E E � 4 4f Ln O O O M O M N Ln Ln N 00 ri H O M O ri 00 I- to ri M O 01 N 0 to N 0) O Ln O O LfI O c I c I a J J a c a) c J a } C } O z O N - u U O U Ln U a M L> 4� o (1c ) 0 o L LIJ C N N 4-+ 4- v L U Q E + to J a o> E ° ° C ° °' c _ 0 I= O W N � J U U J N O S wi LjJ Q L N ` 5 C C L • L • • L_ U U '} U N N N L U z D 0 z >� >� >� Q Q Q Il Ill Q > > > 0 0 0 d d d LL North Lake Dam Spillway Modification City of Coppell n CHOLS Appendix D Opinion of Probable Construction Costs June 2011 ESTIMATOR CHECKED BY ACCOUNT NO Cost Estimate.xlsx 6/13/2011 2:11 PM Page 1 of 3 EXCAVATION Conduit - Excavation 42,640 CY $ 7.00 $ 298,500.00 Conduit - Concrete Removal 1,240 CY $ 75.00 $ 93,000.00 Conduit - Trench Safety 590 LF $ 5.00 $ 3,000.00 Approach Channel - Excavation 21,560 CY $ 7.00 $ 151,000.00 PRINCIPAL SPILLWAY Intake Tower - Reinforced Concrete 65 CY $ 1,000.00 $ 65,000.00 Intake Tower - Structural Backfill 2,850 CY $ 30.00 $ 85,600.00 Intake Tower - Trash Racks 1 LS $ 35,000.00 $ 35,000.00 Intake Tower - Barrier Warning System 1 LS $ 25,000.00 $ 25,000.00 Conduit - 8'x8' Reinforced Concrete Box 590 LF $ 800.00 $ 472,000.00 Outlet Channel - Headwall 1 LS $ 15,000.00 $ 15,000.00 Rock Riprap - 18" max size 3,340 CY $ 75.00 $ 250,500.00 GENERAL ITEMS Mobilization 1 LS $ 75,000.00 $ 75,000.00 Erosion & Sediment Control 1 LS $ 150,000.00 $ 150,000.00 Care of Water 1 LS $ 150,000.00 $ 150,000.00 SUBTOTAL: $1,868,600 CONTINGENCY & TECHNICAL SERVICES 30% $560,580 Cost Estimate.xlsx 6/13/2011 2:11 PM Page 1 of 3 ESTIMATOR CHECKED BY ACCOUNT NO Cost Estimate.xlsx 6/13/2011 2:11 PM Page 2 of 3 EXCAVATION Conduit - Excavation 41,220 CY $ 7.00 $ 288,600.00 Conduit - Concrete Removal 1,240 CY $ 75.00 $ 93,000.00 Conduit - Trench Safety 590 LF $ 5.00 $ 3,000.00 Approach Channel - Excavation 21,560 CY $ 7.00 $ 151,000.00 PRINCIPAL SPILLWAY Intake Tower - Reinforced Concrete 30 CY $ 1,000.00 $ 30,000.00 Intake Tower - Structural Backfill 2,160 CY $ 30.00 $ 64,800.00 Intake Tower - Trash Racks 1 LS $ 35,000.00 $ 35,000.00 Intake Tower - Barrier Warning System 1 LS $ 25,000.00 $ 25,000.00 Conduit - 5'x5' Reinforced Concrete Box 590 LF $ 650.00 $ 383,500.00 Outlet Channel - Headwall 1 LS $ 10,000.00 $ 10,000.00 Rock Riprap - 18" max size 3,340 CY $ 75.00 $ 250,500.00 GENERAL ITEMS Mobilization 1 LS $ 67,000.00 $ 67,000.00 Erosion & Sediment Control 1 LS $ 134,000.00 $ 134,000.00 Care of Water 1 LS $ 134,000.00 $ 134,000.00 SUBTOTAL: $1,669,400 CONTINGENCY & TECHNICAL SERVICES 30% $500,820 Cost Estimate.xlsx 6/13/2011 2:11 PM Page 2 of 3 ESTIMATOR CHECKED BY ACCOUNT NO Cost Estimate.xlsx 6/13/2011 2:11 PM Page 3 of 3 EXCAVATION Conduit - Excavation 66,290 CY $ 7.00 $ 464,100.00 Conduit - Concrete Removal 1,420 CY $ 75.00 $ 106,500.00 Conduit - Trench Safety 730 LF $ 5.00 $ 3,700.00 Approach Channel - Excavation 39,800 CY $ 7.00 $ 278,600.00 PRINCIPAL SPILLWAY Intake Tower - Reinforced Concrete 30 CY $ 1,000.00 $ 30,000.00 Intake Tower - Structural Backfill 4,170 CY $ 30.00 $ 125,100.00 Intake Tower - Trash Racks 1 LS $ 35,000.00 $ 35,000.00 Intake Tower - Barrier Warning System 1 LS $ 25,000.00 $ 25,000.00 Conduit - 5'x5' Reinforced Concrete Box 730 LF $ 650.00 $ 474,500.00 Outlet Channel - Headwall 1 LS $ 10,000.00 $ 10,000.00 Rock Riprap - 18" max size 5,070 CY $ 75.00 $ 380,300.00 GENERAL ITEMS Mobilization 1 LS $ 97,000.00 $ 97,000.00 Erosion & Sediment Control 1 LS $ 194,000.00 $ 194,000.00 Care of Water 1 LS $ 194,000.00 $ 194,000.00 SUBTOTAL: $2,417,800 CONTINGENCY & TECHNICAL SERVICES 30% $725,340 Cost Estimate.xlsx 6/13/2011 2:11 PM Page 3 of 3