C04_Att 4_ Design Rpt Cedar Creek 16.pdf

DESIGN REPORT

For

CEDAR CREEK WATERSHED

SITE 16

REMEDIAL REPAIR

DECEMBER 2024

TABLE OF CONTENTS

CEDAR CREEK WATERSHED SITE 16

REMEDIAL REPAIR

CONTENTS PAGE NO.

Project Description

General Design of Existing Structure

Survey

Repair Work Design

Cultural Resources

Environmental Considerations

Construction Review

Construction Specifications and Bid Schedule

Construction Schedule

Operation and Maintenance

Appendices:

A. Attachment to the Operation and Maintenance Plan

CEDAR CREEK WATERSHED

SITE 16

PROJECT DESCRIPTION

The National Inventory of Dams (NID) identification for Cedar Creek Site No. 16 is TX00791.

The structure is a single-purpose earthen flood prevention dam designed in 1968.

Cons t ruct ion was completed in 1969. The structure is an integral part of the Cedar Creek Watershed (a sub watershed of the Trinity River Watershed). The site is located approximately 7 miles northwest of the city of Terrell, in Rockwall County, Texas. The site is situated within the Blackland Prairie physiographic area of Rockwall County, Texas.

The site was originally built by the Soil Conservation Service, now Natural Resources Conservation Service (NRCS), in cooperation with the Kaufman – Van Zandt Soil and Water Conservation District. It was designed as a single-purpose, low hazard potential, flood retarding structure located in a predominantly agricultural area. It is currently classified as “High” hazard potential by NRCS and the Texas Commission on Environmental Quality (TCEQ). “After field review, at least 2 homes are present downstream of the dam in the potential breach inundation area.” (NRCS Dam Safety Inspection Report, 5/21/2018).

Substantial erosion of the front dam embankment slope and the earthen plunge basin side slopes was documented along with the failure of the principal spillway pipe support in 2019 after a committee organized to conduct a remedial repair investigation made their site visit.

According to the USDA-NRCS Abstract of Engineering Report dated July 12, 2019:

“Excessive erosion to the wave berm and front slope was due to a design deficiency. A vegetative wave berm was designed in an area that experiences fluctuating water levels, and an appropriate stand of vegetation was not established and maintained on the wave berm. A northern facing shoreline also contributed to the erosion.”

and

“The plunge basin side slopes have eroded due to a design deficiency. The erosion has led to failure of the principal spillway pipe support. The original plunge basin should have been armored.”

A site inspection was conducted by the design engineer along with the project sponsor on September 27, 2022; this was to establish the repair area extents, fencing needs, the preferred construction access road, and borrow, waste, and campsite areas.

This repair project is funded through the Remedial Repair Program of the NRCS. The remedial repair will consist of:

Reshaping and armoring the plunge basin in accordance with NRCS Design Note 6, “Riprap Lined Plunge Pool for Cantilever Outlet,”

Rebuilding the upstream slope and wave berm, with rock riprap armoring in accordance with NRCS Technical Release 69, “Riprap for Slope Protection Against Wave Action,”

Building a new, 37.4-foot pipe cantilever, cantilever pipe support, and concrete cradle in accordance with the modified, standard drawing, “Trash Rack, Slide Gate, and Pipe Cantilever Support Details” for 42-inch pipe, and

Replacing the damaged twenty-foot principal spillway pipe outlet section and two (2), ten-foot sections, with a new twenty-foot section and two (2) ten-foot sections of 42-inch pipe.

Installing a new sand filter collar with fine and coarse drainfill around a portion of the pipe sections in accordance with NRCS Chapter 45, Filter Diaphragms, of Part 628 of the National Engineering Handbook (NEH) and Chapter 26 of Part 633 of the NEH.

It should be noted that this site was re-classified as a high hazard potential structure in June 2008. A dam assessment report was prepared in July 2019 by NRCS that included actions that could potentially be taken to rehabilitate the site to meet current dam safety criteria. An official work plan outlining rehabilitation measures has not been prepared. This repair design addresses concerns and challenges observed during past inspections and does not contain rehabilitation measures. Due to its reclassification to high hazard potential, Cedar Creek Site No. 16 is an Engineering Job Class VII structure. All repair and rehabilitation designs for this site will be submitted to the National Design, Construction, and Soil Mechanics Center (NDCSMC) in Fort Worth for independent review.

GENERAL DESIGN OF EXISTING STRUCTURE

Structure Site No. 16 was designed as a low hazard potential structure with an effective height of approximately 20 feet and a length of approximately 2,670 feet. The 1969 as-bui l t drawings indicate that the drainage area is 1,824 acres and the floodwater storage capacity is approximately 1,264 acre-feet.

The original embankment side slopes were designed with 2.5:1 front and back slopes, a 12-foot-wide crest at the top of dam (TOD). The TOD elevation is 498.2 after allowance for settlement. The vegetated, upstream wave berm is 12-foot-wide and is constructed to elevation

487.1. An 18-foot-wide downstream crossing berm was constructed to elevation 492.0.

The auxiliary spillway (AS) is an 80-foot-wide, vegetated spillway constructed on a 3.6% grade (from the crest down to Sta. 12+50) and a 2.1% grade (from Sta. 12+50 to Sta. 17+34). It outlets into a natural channel. The AS crest elevation is 495.0 (between Sta. 10+00 and Sta. 10+50). The AS is contained on the left (looking downstream) by a diversion/dike combination and a dike on the right.

The principal spillway (PS) is 110 feet of 42-inch interior diameter (I.D.), A.W.W.A. C-301 standard pipe (pre-stressed, concrete lined, steel cylinder). The inlet is a 9-foot-high concrete hooded inlet enclosure. The PS is set on a shaped, non-reinforced, Class 2500 concrete bedding. The outlet section is supported by a reinforced concrete pipe support. Two (2) anti-seep collars are located along the PS with a center-to-center distance at 20-feet.

The outflow from the pipe discharges into a 40-foot-wide earthen outlet channel with constructed 3:1 side and exit slopes.

SURVEY

A repair survey was performed by the NRCS Watershed Construction Office in September of 2022. A global positioning system (GPS) survey instrument calibrated to the State Plane Coordinate System (SPCS) was employed for the survey. Rockwall County is in the Nor th Central Zone of the SPCS. The GPS data was then processed using Online Positioning User Service (OPUS). OPUS processes GPS data files with the same models and tools which help manage the nation's Continuously Operating Reference Station (CORS) network. This results in highly accurate and consistent coordinates that can be utilized among varying project stakeholders.

The existing, as built elevation of the reservoir riser crest is 487.6 and has been OPUS corrected to elevation 487.8, a difference of 0.2. This can be attributed to a change in datum from NGVD 29 to NAVD 88. All elevations in the repair construction drawings and in the “Repair Work Design” section of this report reflect the OPUS adjusted elevations. Survey data collected was used to calculate approximate earth and rock quantities required for the repair project.

It should be noted that no change in water surface elevation is planned as part of this repair work design.

REPAIR WORK DESIGN

The scope of this repair is to reshape the existing front embankment wave berm soil, the existing plunge pool/outlet channel soils, and to replace the historically erosive materials with a layer of rock riprap armoring. One (1), twenty-foot section and two (2), ten-foot sections of new concrete pipe; an unreinforced concrete cradle section; a reinforced cantilever cradle; a reinforced pipe support; and a sand filter collar will be installed to replace the damaged PS outlet section as shown on the drawings. An additional placement of armoring, from the plunge basin to the reinforced cradle, will be installed to discourage borrowing animals.

The original Soil Mechanics Report (SMR), January 24, 1968, indicates: PS borehole 301, CL to CH, from 0 to 16 feet and overlaying a shale lens from 16 to 19 feet; and the fill material used to construct the original dam embankment was CL to CH (borrow soils consist of predominately clay, CL-CH materials). The dam was constructed on the Navarro formation, in the floodplain area consisting of alluvial silty and sandy clays (CL & CH) and overlying residual CH and shale.

The shale bedrock is hardness 2.

No other detailed log analysis or engineering properties for the soils were provided in the original file reports. A USDA Web Soil Survey report was ordered for the site so that additional physical and engineering soil properties could be pulled or estimated. The Civil Engineering Reference Manual (CERM) for the PE Exam, Fourteenth Edition, was consulted to estimate typical soil characteristics where site specific soil data was non-existent.

Based on the above sources, the following soil parameters are assumed for the design calculations of this repair:

a saturated unit weight of 118 pounds per cubic foot (pcf), a drained, internal angle of friction of 23 degrees, and a drained cohesion strength of 300 pounds per square foot (psf)

On June 1, 2023, two soil samples were collected from Site 16, one along the center line and within the vicinity of the PS (in Zone 1 embankment materials per the as-builts) and the other along the downstream crossing berm within the vicinity of the PS (in Zone 2 embankment materials per the as-builts). The samples were submitted to the NRCS Soil Mechanics Laboratory in Fort Worth, Texas. On July 13, 2023, a SMR was published and was used in the final design of the sand filter collar. Key findings from the report are:

the base soils are fat clays, CH, with an average plasticity index of 48.5, the base soil is not dispersive, and a seepage filter protection filter/seepage collar of fine aggregate material per ASTM C33 should be included in the final design.

It is reasonable to assume that the existing pipe foundation has been sufficiently consolidated, has adequately supported the previous pipe and cradle, and for that reason is adequate to provide bearing support for new pipe and cradle.

The upstream wave berm repair will consist of:

1. Drawing down the reservoir below the repair elevations shown on the drawings.

2. Stripping and stockpiling the topsoil from the upstream embankment slope.

3. Excavating the upstream slope.

4. Rebuilding the slope with compacted earthfill.

5. Laying geotextile.

6. Placing rock riprap armoring along the slope and around the inlet riser.

7. Placing topsoil on exposed earthfill above the normal water level.

8. Vegetating the topsoil.

Per Construction Specification 21, Excavation, the lower limits of the excavations will be inspected by the assigned construction engineer. The limits of excavation shown on the drawings will be increased if uncompacted earth or objectionable materials are encountered below the lower limit of excavation shown on the drawings. The engineer shall verify and approve these excavations before placement of earthfill. The earthfill to reconstruct the slope, berm, basin, channel, and pipe repair areas will be placed with compaction in accordance with Construction Specification 23, Earthfill.

Calculations were performed to determine the upper and lower extents for placement of rock riprap using criteria established in Technical Release (TR)-69 “Riprap for Slope Protection Against Wave Action”. Multiple, recent NRCS wave berm repair projects within the vicinity of Site 16 used climatic wind data from nearby Dallas, TX. The Method 1 wind speed data of 61.67 mph is taken from that data. The effective fetch length of 1,233 feet was calculated. Averaging wind speed Methods 1 through Method 3 and the Max PGU (peak gust) resulted in a design wind velocity of 68 mph and an adjusted overland wind velocity of 71 mph. The results indicate a significant wave height of 1.61 feet.

TR-69 analysis shows a minimum upper riprap elevation 2.58 feet above the normal pool level and a minimum lower elevation of 2.42 feet below the normal pool elevation. The top and bottom elevations of the rock will be placed at elevation 490.4 (2.6 feet above the normal pool post construction) and elevation 485.2 (2.6 feet below the normal pool post construction) respectively. The rock will be placed on a 2.5H:1V slope. The embankment slope above the rock will be 2.5H:1V or flatter and blend to the existing embankment where the excavation cut daylights with the existing embankment slope. Additional R-150 rock riprap will be placed to elevation 485.8 to replace the local earthen berm (10 x 30 foot) upstream the existing inlet riser lost to erosion and will extend around the inlet’s concrete sidewalls and endwalls. The finished grade of the earthen repair area above the new rock riprap armoring will be 2.5:1 or flatter.

The minimum, W50 rock weight determined from TR-69, is 20.8 pounds. A 20.8-pound spherical rock with a specific gravity of 2.6 has an approximate diameter of 7.3 inches. The selected rock size for this project is ASTM D6092 R-150. R-150 rock has a D50 size of 10.5 inches which is larger and more conservative than the minimum required diameter of 7.3 inches, is widely available to contractors, and has been used effectively in several similar NRCS repair projects.

Further, the larger stone size makes it more difficult for vandals to deface and remove the improvements as designed. The placement depth of the rock normal to the slope/ground will be

2.0 feet.

PS outlet flow was calculated using the “Hooded Inlet Evaluation” spreadsheet. With a 110-foot long, 3.5-foot I.D. PS and an AS crest elevation of 495.0, approximately 147 cubic feet per second (cfs) will flow.

The existing plunge pool and exit channel will be reshaped to install a rock-lined plunge basin and a constructed outlet channel designed for normal tailwater (TW) conditions.

In AutoCAD, the existing plunge pool ground surface area produced from the NRCS survey data was shorter than required and concluded downstream in an apparent reverse grade. A LiDAR/DEM surface was acquired and when placed over the surveyed data, revealed a difference in depth, the NRCS survey producing deeper channel depths.

Using the “Manning’s Equation Analysis: Cross-Section Data” (Version 14, Jan 2013) spreadsheet, “xsecAnalyzer”, maximum TW conditions were determined from the LiDAR/DEM surface. The LiDAR/DEM surface was used to locate the most constraining cross-section. Input values included cross section data points pulled from AutoCAD sections, an “n-value” of 0.035, and a 0.004ft/ft slope calculated over 775 feet of the natural, earthen channel.

Five natural earth channel cross sections, downstream the proposed repair, were modeled for flow capacities:

Station TW Elevation (ft) Capacity (cfs) 5+95 480.13 151.2 7+45.8 480.20 148.4 8+78.3 480.10 152.3 10+55.3 480.12 148.3 12+18.9 479.10 150.7

Also reviewed were Sta. 3+52.6 in the rock riprap basin and Sta. 3+76.2 in the constructed earthen channel. The capacities were 152.12 cfs at El. 478.6 and 156.68 cfs at 478.8 respectively and greater than the design PS spillway flow of 147 cfs.

Sta. 7+47.8 is the most constraining cross section of the five analyzed, causing the highest TW elevation of 480.20. At this elevation the calculated capacity of 148.4 cfs will pass the design PS spillway flow of 147 cfs.

Elevation 480.20 is 4.0 feet below the outlet invert elevation of 484.2 and therefore, TW=-4.0.

With TW=-4.0, the tailwater to pipe diameter ratio TW/Do, -4.0/3.5, equals -1.14. This falls outside the scope of the Rice and Kadavy “Riprap Design for Pipe Spillway Outlets -

Do . Consequently, Design Note 6 (DN6) “Riprap Lined Plunge Pool for Cantilevered Outlet” spreadsheet was used to calculate the minimum dimensions for a new rock-lined plunge basin. Given the resulting output, a rock-lined plunge basin was designed. The design top of rock was set to El. 480.0. This is 2.4-inches below the maximum TW analyzed. Because the ground conditions from the LiDAR surface appear to be shifted slightly higher than the surveyed surface and the plunge basin elevations are based on the survey surface, it is likely conservative to use the cross-sections from the LiDAR surface. Further, given the finished grade variation in R-300 rock riprap with a D50 of 13.5 inches, no negative effects are anticipated by setting the top of rock elevation to El. 480.0.

The final basin design dimensions as shown in the drawings (in length, width, and depth) exceed the minimum calculated DN6 dimensions for a basin constructed of R-300 rock riprap approximately 2.5 feet thick (normal to the excavated subgrade); the final design is a best fit into the existing plunge pool and natural channel footprint. For constructability advantages and to coincide with the existing plunge pool and channel footprint, the design team elected to go with a 25-foot bottom width (instead of the minimum calculated design width (Ws) of 9.8-feet), a deeper depth, and a longer armored basin length.

A rock beaching check calculation in the DN6 spreadsheet confirmed the rock riprap sizing suitability and a “Beaching Controlled” outcome (based on the 13.5-inch, approximate D50 size of the R-300 riprap).

The earthen outlet channel downstream of the rock armoring will be reshaped and transitioned into the existing earthen outlet channel. The capacity of the rock outlet channel was calculated using the “USDA-NRCS Hydraulics Formula”. A 25-foot bottom width, earthen, trapezoidal channel with a 0.0042 ft/ft slope, Manning’s “n” of 0.05, 3:1 side slopes, and a depth of 1.9 feet will carry the projected PS flow of 147 cfs (available depth is 3.3-feet).

The capacity of the constructed earthen outlet channel was calculated using the “USDA-NRCS Hydraulics Formula”. A 25-foot bottom width, earthen, trapezoidal channel with a 0.0013 ft/ft slope, Manning’s “n” of 0.035, 3:1 side slopes, and a depth of 2.2 feet will carry the projected PS flow of 147 cfs (available depth is 3.5-feet).The allowable velocity for a vegetated (Bermuda grass), earthen channel with slopes less than 5% is 6 feet per second (ft/sec) for easily eroded soils and 8 ft/sec for erosion resistant soils; both are greater than the 2.25 ft/sec calculated in the hydraulic model for the proposed earthen channel.

The purpose of the geotextile design used in the rock repair areas is to separate the embankment, plunge basin, and sand filter collar materials, some of which will be underwater, and to provide permanent erosion control. The strength property and survivability class requirements are specified according to guidance in “AASHTO M288 Geotextiles”.

The selection and placement of the geotextile designed for material separation and permanent erosion control purposes (and not for the purposes of subsurface drainage, stabilization, sediment control, or enhancement) will reduce:

Drainage induced failures resulting from clogging or displacement and

Damages from surging conditions along wave berms and plunge basins.

The success of this geotextile design can be observed in similar NRCS repair and rehabilitation rock armoring projects in Texas where it has been installed.

Given the prevalence of the site’s CL and CH material found at all depths and as indicated on the “Geologic Cross Sections of Borrow Area” bore hole data in the as-built drawings (sheet 9 of 11) it can be assumed more than 50% of the embankment and plunge basin subgrade materials will pass the number 200 sieve. For these conditions, a Class I, non-woven geotextile is specified which should also meet the “Requirements for non-woven geotextile” specified in Material Specification 592, Geotextile.

Note that Class I, non-woven product is also recommended by the AASHTO M288-21 Selection Guide as conducive for subsurface drainage and stabilization applications where the percent fines are greater than 50%. Consequently, the new rock riprap wave berm armoring, plunge basin, pipe support footing, and anti-burrowing armored extension will be underlain with Class I, non-woven geotextile.

The geotextile will be placed between the prepared earth subgrade materials and the rock in accordance with:

Construction Specification 94, Contractor Quality Control, section 10a.(8)(g), Geotextile.

Construction Specification 95, Geotextile, section 5, Placement, Method 2, and section 7, Items of work and construction details, 7.a.(1), (2), and (4).

The geotextile shall be keyed into the subgrade at all ends by a minimum of 18”.

A calculated rock placement depth normal to the geotextile covered subgrade (designed to a minimum 2 times the D50 size) is specified.

The plunge pool and outlet section of the existing PS will be repaired, and the following items will be removed:

One (1), twenty-foot PS 42” I.D. conduit outlet section

Two (2), ten-foot PS 42” I.D. conduit sections immediately upstream the twenty-foot PS conduit section

The existing reinforced concrete pipe support; and

The non-reinforced concrete pipe bedding and appurtenances.

To support the existing PS, the area will be excavated to the limits shown in the drawings.

One (1) new twenty-foot section and two (2) new ten-foot sections of A.W.W.A. C-301 reinforced concrete 42-inch I.D. pipe will be installed. The twenty-foot section and two, ten-foot section will be installed over a new 37.4-foot, reinforced concrete cantilevered cradle. The cantilever will be sloped as labelled in the construction drawings. The original 29-foot cantilever concrete and steel quantities are modified to construct the 37.4 cantilever. The additional, 8.4-foot reinforced concrete extension will be entirely earth supported. The cantilever will also be supported by a new, reinforced concrete pipe cantilever support.

The pipe cantilever support and pipe cantilever designs are taken from the USDA Standard Drawing: “Trash Rack, Slide Gate, And Pipe Cantilever Support Details” for 42” I.D. pipe structures.

The pipe support will be installed with its footing sitting on an engineered, 3-foot deep, crushed rock subbase underlain by geotextile. Unclassified downstream embankment excavation is specified in the Construction Specification as shale with a hardness factor of 2 may be encountered during the pipe support excavation.

A sand filter collar will be installed in the vicinity of the pipe repair around the new PS conduit between approximate PS Sta. 2+20 and Sta. 2+55. “The collar is not required to intercept hydraulic fracture cracks in the earthen embankment.” If the pipe repair work is imperfect, “a remote opportunity exists for a flow path to occur along the outside” of the PS conduit “and the purpose of a filter collar is to intercept that flow and provide a filtered, controlled outlet for the collected flow.” “The filter collar only needs to be large enough to collect flow in this space immediately surrounding” the new PS conduit sections (Considerations In Designing a Filter Collar Around a Bored and Jacked Conduit Installation for Existing FWRS by Danny McCook, December 16, 2004).

According to the Conclusions and Recommendations of the 2023 SMR and based on NEH

633.26 “Gradation Design of Sand and Gravel Filters”, ASTM C33 Fine Aggregate will be a suitable filter material for the base soils. The coarse material gradation section of the filter will be selected from the “SAND FILTER COLLAR DRAINFILL GRADATIONS” shown in the drawings.

The sand filter collar dimensions are limited on the upper end (its height) by the eighteen (18) foot crossing berm above it. Guidance in Chapter 45, “Filter Diaphragms” recommends a minimum of two feet of soil cover: “The diaphragm should have a minimum thickness of overlying soil adequate to resist uplift pressures from any crack intercepted.” Requiring a 2-foot soil cover over the proposed sand filter collar allows for approximately 1.3 to 1.6 feet of sand above the pipe conduit depending on the pipe slope.

The dimensions of the sand filter collar below and to the sides of the conduit were sized according to sand filter collar dimensions found in other NRCS projects and according to the document referenced above. The sand filter collar drain outlet will terminate against the R-300 rock armoring of the plunge basin repair. The sand filter collar drain outlet will consist of a coarse gravel portion followed by geotextile followed by the R-300 rock riprap (the new 2.5-foot-thick plunge basin armoring).

For the conduit design:

assumed soil parameters and site repair dimensions were input into the “Joint Gap Computations” spreadsheet designed per NRCS TR-18. The average shear strength of the foundation is calculated as approximately 703 psf. The computed pipe gaps were lower than the historical maximum allowable gaps and deflection angles published by manufacturers, and per the three-edge bearing “Conduit Computation”, NRCS TR-5, the site-specific safe supporting strength for a C-301 reinforced concrete pipe (Reb) founded on a concrete cradle is calculated to be 1,073 pounds per linear foot (plf). The original as-built drawings use 3,000 plf and this is the value input in the STRENGTH REQUIREMENTS table on sheet 9 of the repair drawings.

For the pipe support foundation design the footing’s punching and shear (within the aggregate fill) failure were checked using the “Punching Failure for Strong Frictional Fill Over Soft Cohesive Soil Rectangular Strip Footing” spreadsheet. The computations resulted in passing output with acceptable factors of safety. A 3-foot-thick aggregate fill base (assuming a 130 pcf density and a 35-degree friction angle of fill) in a 4-foot wide by 8-foot-3-inch length, will resist a punching failure by a factor safety of 3 (Qactual is 318 psf and Qallowable at H=3 is 923 psf) and is chosen for this repair project.

The repair areas above and to the edges of all rock armoring will be backfilled with earthen materials, covered with a layer of topsoil, and vegetated over all earthen repair areas.

It is assumed that all fill areas will be supplied by the soil from the cut and borrow areas.

Assuming 25% shrinkage approximately 3,604 cubic yards of fill is required for the repair and approximately 4,987 cubic yards is available from the excavations. This leaves a borrow requirement of approximately zero cubic yards although not all embankment excavation may be reusable. According to the as-built drawings and the recent site visit with the project sponsor, borrow material of suitable quantity and quality appears to be available on site along the right bank of the reservoir (facing upstream). The required borrow materials will be excavated from one borrow area of approximately 1.0 acres, as designated in the drawings. Reserving the top foot of this area for topsoil, approximately 3,227 cubic yards of borrow material remains by excavating approximately 2 feet more into the designated borrow area.

Detailed geometry and construction information can be obtained from the drawings. Topsoil will be placed over all the repaired areas and vegetation established.

CULTURAL RESOURCES

A TX-NRCS Cultural Resource Specialist (CRS) gathered information concerning previously recorded historically or culturally significant sites at Cedar Creek 16 (located at Lat/Long

32.81237 -96.34034) by searching the database of the Texas Historic Sites Atlas (https://atlas.thc.texas.gov/). In addition, other relevant databases were searched including the National Register of Historic Places (https://www.nps.gov/subjects/nationalregister/index.htm) and the National Association of Tribal Preservation Offices (http://nathpo.org/wp/thpos/find-a-thpo/), to identify historically significant sites within the boundaries of the project and Native American interests in the area. Based on a review of these databases, historical imagery, topographic maps, and the Web Soil Survey (WSS) (https://websoilsurvey.sc.egov.usda.gov), there are no previously recorded cultural resources in the area of potential effect (APE), however, an intensive survey of the area of potential effect (APE) and Tribal consultation with Federally Recognized Tribes with Ancestral Interest in Rockwall County is recommended to ensure that no previously unidentified significant sites will be impacted by the proposed project. After consultation with the State Historic Preservation Office (SHPO) and relevant Tribes, and an intensive survey of the APE are complete, and during implementation of the project, an engineer and/or inspector will monitor for previously undiscovered cultural resources during construction, including pre- and post-contact artifacts and features that may appear because of excavation. The TX-NRCS CRS will be notified if cultural resources are encountered in the work areas. Construction activities around the inadvertent discovery will be suspended until the Cultural Resources Specialist provides clearance to proceed.

ENVIRONMENTAL CONSIDERATIONS

Under current regulations of the National Environmental Policy Act (NEPA), Cedar Creek Site 16 is required to have an Environmental Evaluation Worksheet (Form NRCS-CPA-52) completed by an interdisciplinary team to determine the level of NEPA documentation required.

The worksheet has been completed. It is not anticipated that the repair construction of the structure will have any detrimental effects on the environment. The construction specifications call for control of pollution in any form resulting from construction operations. All exposed/disturbed areas not covered with rock riprap will be vegetated to control erosion and provide wildlife food and cover. Vegetative plantings will be part of this contract and shall be done in accordance with the Storm Water Pollution Prevention Plan (SWP3) by the Contractor. The SWP3 also includes the discussion of erosion control measures. The rounding of the edges associated with the various slopes will occur during normal construction operations and this will aid in the blending of the site with the surrounding landscape.

CONSTRUCTION REVIEW

It should be noted that subgrade excavations in the vicinity of the principal spillway conduit shall be carefully monitored to ensure the underlying pipes are not damaged or disturbed. The excavation should be monitored to assure a minimum of 2 feet of cover is maintained over the pipe for 10 feet left and right of the principal spillway centerline.

The embankments bordering the waste areas shall be shaped, smoothed, and revegetated at the end of construction.

The State Design Engineer will be notified of any significant discontinuities in the embankment.

A course of action will be decided upon by consultation with other personnel as necessary and by field review if required.

Policy by the Texas Commission on Environmental Quality (TCEQ) requires new permanent reference markers (PRMs) to be placed on reconstructed dams. The old PRMs shall be located and removed and then replaced with new markers.

Elevation data must be recorded using a survey instrument or survey grade global positioning system (GPS) receiver.

Horizontal and vertical measurements recorded with a GPS receiver must be based on:

The North American Datum of 1983 and

The North American Vertical Datum of 1988.

Latitude and longitude measurements must be provided in decimal degree to six places.

Control points for the layout of the embankment centerline will be established by the NRCS.

CONSTRUCTION SPECIFICATIONS AND BID SCHEDULE

Standard NRCS Construction Specifications have been used to specify the work items to be accomplished during the repair of this site. The various items included in the bid schedule delineate the significant items of work to be accomplished. All subsidiary items are included and discussed in the construction specifications. The bid schedule is concluded to be fair and equitable division of the work for bidding purposes.

A dewatering plan will be specified in the Construction Specifications. Rapid drawdown, exceeding more than 1 foot of reservoir elevation drawdown per day, is to be avoided.

In accordance with Construction Specifications 21, 23, 61, 94 and established construction best practices:

The excavated foundation for all rock riprap shall be examined to ensure all low-density materials have been removed, A stable foundation exists on which to lay geotextile and place rock riprap, The construction engineer shall adjust the excavation limits as necessary to remove the materials if low density materials are still present, Open excavations should be backfilled in a timely manner to ensure the density and moisture requirements for the material are maintained at specific levels, All excavated subgrade or earthfill materials that exhibit drying cracks, slaking, and other evidence of being unsuitable shall be removed or reworked prior to placement of fill, At the discretion of the construction engineer, Bid Item No. 8 unit rates for excavation will be paid to the contractor for the removal of saturated cut material.

CONSTRUCTION SCHEDULE

There may be some shutdowns and delays due to unforeseen weather events. Approximately 179 calendar days (holidays and weather days not included) will be required to complete this repair.

OPERATION AND MAINTENANCE

Operation and maintenance of this site is the responsibility of the Sponsoring Local Organization (SLO) and will be subject to periodic inspection and review by the NRCS. A copy of the operation and maintenance agreement is on file in the NRCS State Office and is a standard agreement for operation and maintenance.

The Sponsors shall include periodic inspections of the repaired areas for indication of potential slides, wave erosion, rilling, and deteriorated and/or displaced rock riprap, and damaged or displaced vegetation.

A good vegetative cover shall be established and maintained on the site (particularly on the repaired areas). Remove excessive and/or undesirable vegetative growth; remove excessive debris; restore slopes and berms; and reestablish vegetative cover as needed.

Designed By: Concurred With:

Date Date

GARY E. GERACI, E.I.T. R. BRIAN WENBERG, P.E.

Design Engineer NRCS, State Conservation Engineer NRCS Temple, TX Temple, TX

GARY

GERACI

Digitally signed by GARY

GERACI

Date: 2024.12.20 15:15:52 -06'00'

APPENDIX A

CEDAR CREEK WATERSHED SITE 16

ATTACHMENT TO THE OPERATION AND MAINTENANCE PLAN

Operation and maintenance of this structure will be the responsibility of the SLO and subject to periodic inspection and review by the NRCS. A copy of the O&M agreement is on file in the NRCS State Office and is a Standard agreement for operation and maintenance agreement.

a. Inspection

(1) Rock armoring along the wave berm and within the plunge pool/outlet channel;

constructed earthen channel - check for deterioration or displacement of rock, settlement of earthfill, quality of vegetation stand, needed woody brush/weed control, and sediment and debris deposition.

(2) Embankment slopes – check for cattle induced erosion and back-slope toe erosion caused by neighboring residential improvements.

(3) Fences - check for: deterioration of coatings and/or materials; bent or overturned line, brace, stub out, corner, and gate posts; and adequate tension of line and brace wire. Inspect swinging gates for proper opening and closing.

b. Maintenance

(1) Rock armoring along the wave berm and within the plunge pool/outlet channel;

constructed earthen channel - remove sediment and debris depositions; remove undesirable vegetative growth; replace or repair displaced rock; and replant poor vegetation stands within the vegetated areas indicated on the drawings.

(2) Embankment slopes – repair trail erosion caused by cattle traffic and ensure cattle do not loiter on the dam; add and maintain rock riprap along the back toe of the dam where neighboring residential improvements have caused erosive channel flow during rain events; and replant poor vegetation stands within the vegetated areas indicated on the drawings.

(3) Fences - replace line, brace, stub-out, corner, and gate posts that are excessively deteriorated, damaged, bent, or overturned; replace excessively deteriorated wire and stays; and restore adequate tension of line and brace wire.

Replace or repair any damaged swinging gate components that prohibit proper closure and securing of gates.

(4) Control beaver/rodent activity at the site on a regular basis.

Prepared by:

Date

GARY E. GERACI, E.I.T.

Design Engineer NRCS, Temple, TX

GARY GERACI Digitally signed by GARY GERACI Date: 2024.12.20 15:16:22 -06'00'