UPPER BRUSHY CREEK WATER CONTROL AND IMPROVEMENT DISTRICT DAM 7 MODERNIZATION AMERICAN PUBLIC WORKS ASSOCIATION, TEXAS CHAPTER

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1 UPPER BRUSHY CREEK WATER CONTROL AND IMPROVEMENT DISTRICT DAM 7 MODERNIZATION AMERICAN PUBLIC WORKS ASSOCIATION, TEXAS CHAPTER PUBLIC WORKS PROJECT OF YEAR NOMINATION STRUCTURES, $5 TO $25 MILLION INTRODUCTION The Upper Brushy Creek Water Control and Improvement District (District) maintains 23 earthen flood control dams in Williamson County (County) that were built by the U.S. Soil Conservation Service (SCS) in the 1960 s when this area was agricultural farmland. The County was predominantly rural at the time and the dams were mostly classified as low hazard. Since that time, the County has experienced a drastic population increase, with development occurring downstream from all the dams. This development made the dams become critical infrastructure for public safety and considered as high hazard. This reclassification imposed higher safety standards, and all of the District s dams required rehabilitation to meet the State s criteria. For the past 15 years, the District has been executing a dam modernization program, with this project marking the 20th dam to be modernized. Upper Brushy Creek Floodwater Retarding Dam No. 7 (Dam 7) is one of the largest and most visible of the District s dams. Dam 7 is a high-hazard dam located on the border between the Cities of Austin and Cedar Park within Williamson County. The dam is a popular recreational destination due to an adjacent city park, and the regional hike-and-bike trail that crosses the dam. Dam 7 did not meet state dam safety hydrologic requirements as regulated by the Texas Commission on Environmental Quality (TCEQ). True to its mission, the District began a modernization effort that kept flood control and dam safety at the forefront. Freese and Nichols, Inc. (FNI) designed the modifications to the dam to meet dam safety requirements. The project was much more than a typical dam rehabilitation project due to the regional trail. An innovative design was required to increase the auxiliary spillway capacity while accommodating the trail and keeping the project footprint within a very limited easement area. A labyrinth weir was selected as a practical solution due to its ability to maximize discharge within a limited width. The design of the labyrinth included extensive hydraulic modeling to develop a site-specific design (see Additional Considerations section). The labyrinth required significant excavation in the auxiliary spillway to align the crest with the existing spillway; thereby also reducing visibility of the new structure from adjacent properties.

2 In addition, the project included unique architectural and landscaping features to incorporate the new concrete structure into the recreational and natural surroundings of the site (additional information in the Community Relations section). The project provided a comprehensive upgrade to the dam that also included riprap replacement on the upstream slope, in conjunction with the trail replacement, and relocation of an existing wastewater line in the spillway. CONSTRUCTION SCHEDULE, MANAGEMENT AND CONTROL TECHNIQUES The project was awarded to ASI Constructors, Inc., (ASI) as the best value contractor, and construction formally began on June 27, The original substantial completion date for the project was set for August 14, 2017, but it was achieved approximately six months late on March 8, The duration of the project was formally extended by 20 days via change orders due to foundation drain system modifications, extension of a retaining wall for the trail, and an additional access ramp in the spillway. The main factors for substantial completion occurring behind the contracted date are discussed as follows: ROCK EXCAVATION Substantial rock excavation (approximately 35,000 cubic yards) was required for installation of the new spillway. The excavation was performed in two phases: At the beginning of construction to expose the foundation of the new spillway, and near the end of the project to create the spillway s approach channel. Rock excavation took longer than originally anticipated by the contractor. Project restrictions precluded drilling and blasting, and normal removal practices, such as hammering or ripping, were Milling machine excavating limestone rock found ineffective due to the rock s composition. The project team ultimately utilized milling equipment, which provided adequate production rates and allowed for tighter tolerances in achieving the lines and grades of the foundation and channel; thereby minimizing the amount of re-work to prepare for successor work activities. The milling method also produced a rock byproduct that was able to be used in several other areas across the project site, including construction of the water control cofferdam, which otherwise would have required the import of suitable materials. GROUNDWATER Weathered seam in spillway foundation After excavating the spillway, a weathered seam in the foundation rock was discovered which produced significant groundwater. Contract modifications were issued to revise and increase the extents of the drainage systems under and adjacent to the spillway structure. The robust drainage systems were installed successfully and regularly produce groundwater. SALE OF CONTRACTOR The prime contractor, ASI Constructors, Inc., had a 30+ year history working in the water resource construction industry, specializing in dam rehabilitation and construction. During construction, for reasons unrelated to this project, the prime contractor fell upon financial difficulties and ultimately sold many of its assets to an unrelated

3 third party that owns a group of companies specializing in, among others, heavy civil, dam and specialty geotechnical construction industries. On March 27, 2017, Shaft Drillers International LLC, through its wholly-owned subsidiary, ASI Construction LLC, purchased substantially all operating assets and hired most of the employees from the prime contractor, ASI Constructors, Inc. As a result of the sale, construction of the project was suspended while the prime contractor s surety, working closely with the District, evaluated the status of the project, along with the capabilities and resources of the new company, ASI Construction LLC. Ultimately, with the recommendation of the District, the surety deemed ASI Construction LLC as the most qualified to complete the job and the best solution to mitigate the impact to the overall project schedule. The prime contractor subcontracted ASI Construction LLC to complete all remaining scope of work. Once construction activities resumed, ASI Construction LLC worked overtime, restructured the project schedule and increased staff to make up for lost time. Despite achieving substantial completion late, ASI Construction LLC accelerated site restoration efforts to be ready for the ribbon-cutting event only one month after substantial completion. The sale of the prime contractor in the middle of construction was unusual and led to schedule impacts; however, the project team was able to stay onsite to complete the project and performed high-quality work. The completed project was well received by the District, the County and the public. SAFETY PERFORMANCE AND OVERALL SAFETY PROGRAM SAFETY PERFORMANCE SAFETY STATISTICS The construction safety performance for the project was excellent, with no lost time due to accidents. The construction phase was very labor intensive given the complexity of the structure and the architectural enhancements. TOTAL MAN-HOURS WORKED: 98,064 LOST-TIME INJURIES ON THE PROJECT = 0 INCIDENT RATE = 4.1 OVERALL SAFETY PROGRAM ASI Construction LLC was committed to accomplishing all work activities in a safe manner and pursued a safety program that provided a safe and healthful workplace for ASI Construction employees, its subcontractors, vendors and other project partners. ASI Construction recognized the following factors as being critical to meeting its goal of providing a safe and healthful workplace: preventing workplace injuries, knowledge of safe work practices, knowledge of safety and health regulations and working together as a team to "make it happen." Personal Protective Equipment at all times ASI Construction placed the safety and health of its employees, other contractors and their employees ahead of its production requirements. No employee, vendor, subtier contractor or project associate of ASI Construction was asked or allowed to perform work in known dangerous or potentially dangerous conditions. ASI Construction also encouraged its project partners to immediately report unsafe conditions or actions directly to project managers or the company Safety Director. Safety at ASI Construction was accomplished through the utilization of project safety teams comprised of a site safety representative and members of the project management team. Throughout the project, the site safety representative was required to be onsite whenever work was being performed. This individual oversaw the implementation of the safety plans and procedures. Employee safety awareness was accomplished through daily crew task planning, safety meetings, weekly safety assessments and topic specific safety training seminars. In addition to accident prevention, ASI Construction focused on incident prevention by requiring all near miss incidents be immediately evaluated to mitigate future occurrences.

4 ENVIRONMENTAL CONSIDERATIONS Permitting and regulatory reviews are an important aspect of any dam rehabilitation project. The design and construction required numerous special steps to protect the environment, endangered species and water quality, which are outlined as follows: During preliminary design, FNI evaluated the proposed project area for impacts to any threated and endangered species. Biologists visited the site and conducted a threated and endangered species habitat assessment; no suitable habitat was observed for any of the federally listed or state listed species. FNI evaluated the proposed project area for impacts to potential Waters of the U.S. o A field survey was performed by FNI to determine and map wetland boundaries, and it determined that a seep downstream of the dam produced groundwater regularly and created shrub/scrub and herbaceous wetlands downstream of the spillway area. Therefore, the limits of construction were restricted in the spillway area to prevent disturbance of the wetland. Mulch sock was placed along the limits of construction to protect this area from sedimentation. The small portion that was disturbed was replanted with wetland vegetation species and protected during restoration. o Permitting was required by the United States Army Corps of Engineers (USACE) for placing fill within the Waters of the U.S. for the upstream slope riprap replacement in the reservoir. A preconstruction notification was required for the project, prepared by FNI, and approved by USACE prior to the start of construction. The site is located in the Edwards Aquifer Contributing Zone and had to meet the additional requirements of the Edwards Aquifer Rule. A karst survey was performed for the project area, and no karst features were identified. A contributing zone plan was required for the project, prepared by FNI, and approved by Texas Commission on Environmental Quality (TCEQ) prior to the start of construction. Per federal, State and City requirements, a Storm Water Pollution Prevention Plan was required, and FNI stipulated erosion and sediment controls utilizing best management practices in the construction documents. Throughout construction, FNI inspected the erosion and sediment controls to verify compliance with the plan. The site is located within the City of Austin, and an Environmental Resource Inventory was required for the project due to proximity to waterbodies. Additional review by the City was required to perform construction on this site. The project limited the clearing of trees and vegetation to the extent practicable and upon completion, included planting native trees and vegetation adjacent to the regional trail. Natural area with wetlands downstream of old trail switchback

5 COMMUNITY RELATIONS PROTECT PUBLIC LIVES AND PROPERTY The State dam safety regulations are in place to protect the public s safety, especially for residents and businesses located downstream of the dam. The State dam safety program monitors and regulates dams in Texas to help owners maintain safe facilities and minimize the risk of dam failures, which can cause property damage, personal injury and loss of life downstream of the dam. Existing dams often need to be upgraded in response to aging infrastructure and development occurring downstream. The purpose of this project was to upgrade Dam 7 to meet current safety regulations; thereby protecting public lives and property downstream of the dam. As a flood control dam, Dam 7 is designed to hold 1.1 billion gallons of floodwater as the lake level rises, and then release it slowly over the course of many days through the principal spillway pipe at the bottom of the dam. Once the storage amount is exceeded in large flood events, additional flows must be passed through the auxiliary spillway to prevent the entire embankment from being overtopped by the lake. Earthen embankment dams are not designed to withstand overtopping flows and can be eroded away resulting in failure of the dam. The new labyrinth spillway, due to its longer crest length from the zig-zag shape, can pass significantly more flow than the old spillway while staying within the same footprint. The new spillway will safely pass the required design flood and avoid overtopping the dam; thereby protecting the dam and downstream residents. Dam prior to rehabilitation holding water after flood event in 2010

6 PUBLIC OUTREACH During early phases of design of the project, the District and the County held two public open houses in the adjacent city park to inform the public of the project, educate them on the purpose and function of the dam, and gather input on aspects related to the regional trail. The public eagerly provided feedback that the trail is a very important part of their everyday lives. The District also coordinated with local media to provide news articles on the project for those who could not attend the open houses. A rendering of the project was developed to share the concept with the park and trail users. A comparison of the rendering and actual project photo is provided below. Public Open House in 2015 Project Rendering from 2015 Aerial photo after completion in 2018

7 TRAIL IMPROVEMENTS AND AESTHETIC ENHANCEMENTS The District partnered with the County to upgrade 3,300 linear feet of trail across the entire dam embankment and the new spillway. The new trail is ADA compliant featuring colored concrete and a decorative steel handrail. The integral-colored concrete required considerable attention to the handling and mixing of the dye used in over 100 separate ready-mix concrete deliveries to provide a uniformly colored product across the entire trail. The trail width was increased by two feet, to a 12foot-wide trail across the entire upstream slope of the dam to improve passing pedestrian and bicycle traffic. A scenic overlook area was added on the crest of the embankment, which faces the labyrinth spillway with benches shaped like the spillway baffle blocks. 12 wide trail on upstream slope To traverse the downstream slope of the dam, switchbacks are required to drop 40 feet in elevation within a span of 300 feet. The trail switchbacks on the downstream slope of the dam were lengthened from the previous trail to reduce the grade of the incline. Construction of the trail switchbacks required extensive field collaboration between ASI Construction and FNI to account for adjacent items of work and ensure the various grade changes were constructible and ADA compliant. The design team incorporated the following architectural and landscaping features into the spillway structure to embrace the recreational and natural surroundings of the site: Extensive landscaping layout of native trees, plants and limestone boulders to line the trail. Concrete formliners with architectural features on the spillway training wall facing the trail switchbacks. Backfill for plantings and crushed granite for the trail across the impact basin of the spillway. Decorative fossil stamps on the baffle blocks adjacent to the trail across the spillway. Formliner and fossil stamps on structure Concrete formliners to mimic natural limestone installed on the vertical faces of the stepped spillway adjacent to the trail. Trail switchbacks on the day of the trail opening

8 Ribbon-cutting Event on April 18, 2018 RIBBON-CUTTING PUBLIC EVENT The District and the County held a joint ribbon-cutting event on the new overlook at the dam to celebrate the completion of the dam modernization project and officially open the trail to the public. The event highlighted the interagency cooperation that made the project such a success. Attendees included staff and elected officials from the District, Williamson County, and City of Cedar Park, as well key project team members from FNI and ASI Construction, media and enthusiastic trail users from biking groups to runners and walkers. Articles in the local media covered the event. From the Austin American Statesman on April 18, 2018: The district started a project to modernize them in 2003 and now has modernized 20 of them, including the $18 million construction project for dam #7, said Jeff Sawyer, the president of the Upper Brushy Creek Water Control and Improvement District Board. This is our showpiece, said Sawyer at the ribbon cutting at the dam on Wednesday and citing the beauty of the lake area around it. ADDITIONAL CONSIDERATIONS INNOVATIVE HYDRAULIC DESIGN Like many SCS flood control structures, the auxiliary spillway at Dam 7 is located on an abutment; however, the spillway approach channel creates a substantial flow angle (an approximate 70-degree bend). Initial assessments used published data for labyrinth weir design; however, additional analyses were required to evaluate the effect of the approach angle and develop a site-specific design. Computational fluid dynamics (CFD) and physical hydraulic models were performed as part of the labyrinth spillway design. The modeling results showed there was an approximate 35% decrease in hydraulic capacity as compared to the same labyrinth weir designed using published data (which assume the weir is perpendicular to the flow). However, even with the 35% reduction, the labyrinth weir substantially increased the hydraulic capacity from the existing broad-crested weir and passed the required flow. The site-specific design through modeling was critical to the labyrinth spillway hydraulic design at Dam 7. The models provided a better understanding of the design and confidence the project goals were met. The CFD was a cost-effective approach to determine the labyrinth spillway CFD model

9 configuration and size that would pass the required flow. The physical model was used to refine the design to maximize discharge, minimize required excavation of the approach channel and evaluate options for downstream energy dissipation. The total cost of the modeling constituted approximately 10%of the design fee and 1% of the anticipated construction cost. The physical modeling was estimated to reduce construction costs by over 2% of the anticipated cost. The physical model also provided a visual understanding and hands-on design approach for the owner and design team. In 2016, the owner and design team published a paper on the Importance of Site Considerations for Labyrinth Spillway Hydraulic Design as part of the United States Society on Dams Annual Meeting to share the design approach and findings with other dam owners and engineers. Physical model WASTEWATER LINE RELOCATION An existing wastewater line passed through the spillway of the dam, and installation of the new labyrinth weir would prevent maintenance access to the line. The local water utility partnered with the District on the project to relocate the line around the spillway to avoid conflict with the dam. Installation of the majority of the line required trenchless technology. Design for the new line included groundwater monitoring for baseline conditions and coordination with the dam design team to determine an appropriate alignment. Due to the specialized aspects of the wastewater and spillway construction, the District and FNI hosted site tours during construction to share the project with other local engineers, owners and regulators. Site Tour with other dam owners, regulators and design engineers