DESIGN-RELATED CONSTRUCTION CONSIDERATIONS

Transcription

1 CHAPTER 19 DESIGN-RELATED CONSTRUCTION CONSIDERATIONS 19.0 OVERVIEW In the completion of PennDOT's transportation improvement projects, different personnel perform the design and construction functions. To successfully and efficiently complete a project, adequate communication between the two segments of the project team is essential. Design personnel should be aware that there are construction-related design considerations, and construction personnel should be aware that there are design-related construction considerations. Thus, it is very important to have good communication between design and construction personnel. When problems arise, it is crucial that the issues be discussed in a timely manner, and a workable solution decided upon. To facilitate open and unhindered communication between the design and construction portions of the project, a forum for design-construction related discussion sessions should be provided on a regular basis. Such a forum helps to reduce or eliminate redundancies and adherence to archaic methodologies by developing the most viable solution(s) based upon the expertise of both types of personnel. There are different avenues and forums for the design and construction personnel to discuss design and construction issues. Depending on the type of project these sessions should begin at the pre-bid stage or at the latest the preconstruction stage and continue through the final inspection conference. Regardless of when and how often meetings occur between the design team and construction personnel, the familiarity of design personnel with PennDOT publications such as Publication 13M, Design Manual, Part 2, Highway Design; Publication 15M, Design Manual, Part 4, Structures; Publication 72M, Roadway Construction Standards; Publication 408, Specifications; and conformance with PennDOT's drainage policies can help reduce the number and complexity of questions during construction. Open communication between design and construction personnel is essential and eventually results in good working relationships. Ultimately these relationships help to improve designs and ensure that projects are constructed as envisioned without major problems or field revisions DRAINAGE DESIGN AND CONSTRUCTION A. Relationship of Construction to Design. Construction-related hydrologic and hydraulic considerations are a necessary part of the planning and design phases of a project. Factors that may affect construction timing and methods need to be considered as project development proceeds and need to be supported by appropriate design computations. A few common drainage-related factors that may be encountered and affect construction, for consideration during design include: Seasonal fluctuations in flow. Variable water surface elevations. Groundwater elevations. Environmental constraints (i.e., seasonal limitations on in-stream construction due to fish migration). Construction staging. Availability of materials. Construction easements. Construction access. Maintenance and protection of traffic. Constructability. Any special or unique construction requirements should be communicated to the designer prior to the final design phase of the project. Correspondingly, special instructions to the contractor are to be included in one of the project's Special Provisions. The designer should be prepared to explain important aspects of the design during the preconstruction conference and meetings with the construction team. Before designing or specifying any unique and complex component of a project, the designer should consult with the District's Maintenance Unit to ascertain if there are any special considerations that need to be accommodated for in the design in order to maintain the proposed improvement. It is important that the designer obtain feedback from individuals familiar with typical 19-1

2 construction practices and methods in order to understand the impact of any special provision or complex component of the project upon the project construction schedule. Department personnel responsible for contract administration and construction may need to coordinate their scheduling and construction procedures with the designer to achieve the intended results. B. Cost Considerations. Cost is an important consideration in any design. A large portion of the initial project costs are related to materials and construction. However, future maintenance and replacement costs are a very important aspect of the overall project cost. For a project to be effective, an appropriate balance between material, construction, maintenance, and replacement costs is necessary. Ordinarily, material costs are optimized by using readily available materials in a consistent manner, recycling materials, researching programs to identify new construction materials and how they may be utilized efficiently, using reasonable safety factors in design and encouraging and allowing the use of alternatives wherever possible. In some cases, the least expensive material may not always provide the best value, especially when considering the project costs over the service life of the project. This is because even though certain materials and installation costs may be higher than their less expensive alternatives, certain materials may offer a cost advantage in the areas of future maintenance and replacement that override the initial material cost advantage. For example, geosynthetics may be an advantageous alternative to granular filter materials in some situations. Typically, construction costs are affected by the following items: Relative difficulty of construction. Laws, rules and/or regulations governing construction procedures. Degree of competition among contractors. Construction latitude allowed by the specifications. Degree of use of standardized construction details and specifications. Quality of the construction plans. Degree of supervision and inspection provided by PennDOT and regulatory agencies. The choice of certain construction procedures may be of more value than less complicated and less expensive counterparts if they allow for the use of more economical materials, minimize maintenance costs and eliminate or reduce the need for replacements. C. Environmental Considerations. The designer should work with other disciplines as necessary to devise and construct mitigation measures that protect and reduce the adverse effects of the project upon sensitive environmental features near the project. The designer is to consider, evaluate and propose locations and sizes for hydraulic facilities (e.g., culverts, bridges, channels), spoil disposal areas, geometry, construction staging and various construction alternatives for all elements of the design. Each element is to be developed in an effective context sensitive solution that also adequately addresses the project's environmental needs and commitments. The designer may also assist in developing programs for protecting surface waters during construction which include but are not limited to: Levees and ponds to collect various types and quantities of pollutants including those from construction equipment or which are accidentally spilled. Methods to reduce erosion and sedimentation. Means of replicating the natural hydrologic regime and hydraulic response of surface waters that are affected by construction. More information on these programs can be found in Chapter 3, Policy, Chapter 11, Surface Water Environment; Chapter 12, Erosion and Sediment Pollution Control; and Chapter 14, Post-Construction Stormwater Management. D. Water Quality. Water quality of streams and lakes is a very sensitive issue. Construction of drainage systems and non-drainage appurtenances alike may deliver such things as sediment and chemical constituents associated with construction activities to streams, rivers and lakes unless precautions are taken. Precipitation gauges and streamflow data indicate that very low stream flows occur periodically throughout the year. During these periods, even small amounts of additional sediment or chemicals entering the stream from construction areas could be detrimental because of the low dilution effect provided by the receiving waters. Although it is important to control 19-2

3 the inadvertent transport of material from the construction site during normal conditions, it is crucial to control the inadvertent transport of sediment and chemicals from the construction site during times of very low flow. Generally, the more environmentally sensitive a site or receiving water body is the more safety measures and precautions are needed to control the inadvertent transport of chemicals and materials from the site. The effects of sediment or chemicals from highway construction during the low-flow periods should be investigated for sensitive areas (e.g., where stream flow is used for municipal water supply, areas with threatened or endangered species). This investigation may include periods of water quality monitoring and testing. If the investigation concludes that the amount of sediment or chemicals may exceed an acceptable threshold value, the construction periods may have to be adjusted or additional mitigation measures employed to protect the sensitive features. In some extreme cases, water quality testing or monitoring may be necessary to ensure the protection of such sites, especially if the groundwater or water from the stream is being removed for construction purposes. Normally any work in or around surface waters requires regulatory permits before the work can be performed. Resource management agencies, such as the Pennsylvania Department of Environmental Protection, Pennsylvania Fish and Boat Commission, Pennsylvania Department of Conservation and Natural Resources, Pennsylvania Game Commission, U.S. Army Corps of Engineers and the Federal Emergency Management Agency should be consulted early and often in the design phase of a project whenever work is proposed within a floodplain or channel. PennDOT has developed a series of publications related to various aspects of environmental approvals and clearances. For further information and guidance on water quality and the environmental clearance process, refer to these publications: Publication 10B, Design Manual, Part 1B, Chapter 3, Categorical Exclusion Evaluations; Publication 10B, Design Manual, Part 1B, Chapter 4, Environment Assessments; Publication 10B, Design Manual, Part 1B, Chapter 5, Environmental Impact Statements; Publication 13M, Design Manual, Part 2, Highway Design; Publication 325, Wetland Resources Handbook; and Publication 349, Section 4(f) Handbook, Volumes 1 & 2. Publication 689, Transportation Project Development Process: Cultural Resource Handbook. E. Effects of Changes. Problems may be avoided during construction when important drainage or other waterrelated factors are adequately considered during the Engineering and Environmental Scoping Phase of the project. To better understanding a proposed project's potential scope of work it is often desirable and helpful to include input from county maintenance personnel in the scoping phase of a project as they may have first-hand knowledge of existing drainage and environmental issues associated with a particular site. Whenever possible, known problem areas should first be avoided and only if avoidance is not possible then minimization or mitigation measures should be considered. A site may be considered a problem location for any number of reasons including adverse geological features, environmental concerns, sensitive existing facilities or other issues that might conflict with the proposed project. By avoiding the problem the project designer can reduce the need for any future changes to the proposed or temporary condition when things change and field parameters are different than those used in the design. The design process is an iterative process that requires input from many different engineering disciplines to efficiently and effectively develop an appropriate drainage or hydrologic and hydraulic design that is acceptable to the regulatory agencies issuing permits for projects. Throughout the design process, the project design should be periodically checked to verify that site conditions are consistent with actual field conditions. Channel meander, migration, bank caving, aggradation, headcutting or other natural or man-induced changes in channels can occur rapidly and can significantly affect the final design of hydraulic structures. Development within a watershed, grading changes and the alteration of land cover and existing drainage infrastructure can all impact stormwater and cause a needed change in a proposed design. If an extended period of time occurs between the project survey and the design, or the design and construction, the designer may need to reconsider design decisions that were based on field conditions that no longer exist. Being aware of the potential for change and the location of potential changes can help the designer develop a project that is easier to construct and which requires less field changes to achieve the intended objective of the drainage design. 19-3

4 19.2 DESIGN PROCEDURES / PROCESSES RELATED TO CONSTRUCTION A. Construction Plans. The designer is to be aware of the relationship of the drainage design to other aspects of the project in order to fully understand how these elements affect construction costs and to effectively evaluate their intended performance and impact upon the design. Construction plans prepared by the designer should reflect these considerations by containing: Construction sequences that consider construction costs, environmental considerations and public convenience. Subsurface soil borings. Detour plans. Complete descriptions of utilities. Consistent plan format that enhances the contractor's ability to assimilate and understand PennDOT's plans and contract documents. Despite the most careful efforts, construction changes are occasionally needed that deviate from the information shown on the construction plans. Regardless of the size or location of these modifications, the contractor needs to consult with the PennDOT Project Manager, and if deemed necessary by the Project Manager, the designer, before these changes are implemented as they may affect the proper functioning of the drainage facilities or hydraulic structures. B. Constructability Review. To reduce the possibility of developing a design that cannot be constructed, it is important that all elements of the drainage design and design of hydraulic structures undergo a constructability review. A constructability review is a necessary part of the drainage design as drainage issues often impact or are impacted by many other facets of a project. The focus of such a review is to provide confidence that the various elements included in the design can be constructed and function as intended. Some items that may complicate or impact the constructability of a drainage design or hydraulic structure include: Environmental permitting. Safety issues. Material availability. Construction access. Right-of way requirements. The time necessary to complete such a review varies depending on the complexity of the design. To obtain a good assessment of the constructability of the drainage design, the review should be completed by an experienced individual or team of individuals that are familiar with drainage, knowledgeable of several different related engineering disciplines (i.e. traffic, right-of-way, structures, highway safety, environmental) and aware of current construction materials, methods and issues. To minimize the amount of rework needed during the construction phase of a project, several reviews may be warranted throughout the design process on large or complex projects. The level of effort associated with a constructability review should be commensurate with the overall cost and complexity of the project. C. Shop Drawings. Design drawings and their supporting documentation often do not include sufficient detail necessary to manufacture very specialized components of a drainage system or structures when non-standard components or materials are specified in the design documents. In such a case, shop drawings may be needed to direct the manufacturer how to fabricate a particular structural element of the drainage design based upon its intended use. Shop drawings are only needed for very specialized elements of the drainage design that are not fully addressed in Publication 72M, Roadway Construction Standards, Publication 219M, Standards for Bridge Construction, or Publication 408, Specifications. Very specialized elements of the drainage design may include certain concrete culvert configurations, irregular inlet boxes or manholes, outlet control structures, or end treatments for culverts. In such cases, shop drawings may be warranted to provide specific details on how elements of the drainage design are to be manufactured and to identify appropriate materials to use so that these elements of the drainage design would be structurally sound and fully capable of functioning as intended throughout the project's service life. 19-4

5 Design professionals involved in the drainage design or hydraulic analysis occasionally get involved with the review of shop drawings. To minimize the need for shop drawings, designers are encouraged to specify the use of standard pre-approved PennDOT materials and products wherever feasible. See Publication 10C, Design Manual, Part 1C, Transportation Engineering Procedures, for more information on this topic. D. Value Engineering. The purpose of value engineering is to eliminate, modify or combine any project elements, including elements of the drainage design or hydraulic structures that add cost to a project but do not add value. Since these unnecessary elements do not add value to the project, they may be altered or removed from the project as needed, with approval from PennDOT, if it can be demonstrated that the alteration or removal of such elements do not affect the function or overall performance of the project. Establishing the value of certain elements is not always readily apparent since the overall value of each element is assessed based on its value not just at the time of construction but for the overall service life of the project. To accurately assess the value of a specific project element, it is important to consider its function and cost for the entire project service life and not just the construction portion of the project alone. In other instances, even when an element of the design appears as if it does not add value, the feature may not be readily modified or eliminated. This may be the case when certain project features are incorporated into a design based upon regulatory requirements (e.g. stormwater BMPs). Often, alteration of these features requires a permit modification to implement the value engineering. Typically, these analyses require insight from many different disciplines to accurately assess the value of a particular element. Although drainage and hydraulic design are only a small component of most transportation projects, there are few areas of the project that are not affected by drainage. For example, it may be of more value to install curbing to control stormwater on a given segment of roadway, to separate project drainage from offsite drainage, than it would be to allow both offsite drainage and project drainage to combine. Combining the stormwater could require a larger stormwater management facility to control stormwater for the project. In such a case, a single drainage issue could potentially impact roadway geometrics, right-of-way requirements, roadway safety, maintenance requirements, environmental approvals and other elements of the roadway's design. Value engineering is normally reserved for larger more complex projects where the cost to complete the analysis can be offset by project savings. Although value engineering is not exclusively related to the drainage design, such an analysis cannot be completed without considering the impact of drainage upon the project. See Publication 10C, Design Manual, Part 1C, Transportation Engineering Procedures, for more information on value engineering. E. Project Partnering. Project partnering is a process that emphasizes a multi-discipline team approach to completing projects on-time, within budget and without disputes. The process is typically employed on large, complex, highly visible projects that involve major stakeholders which may be subject to critical time constraints and/or involve highly sensitive environmental features. Drainage design and the construction of hydraulic structures are often integrally related to sensitive environmental features such as Pennsylvania Code Chapter 93 designated high quality or exceptional value streams and wetlands. Although the drainage design and eventual construction may not be of sole focus in such sessions, the commitments that are made in the partnering process to preserve and restore various aspects of a project can have a significant impact upon a project's drainage design and construction. The partnering process is meant to foster cooperation between PennDOT, its designer, regulatory agencies, and major stakeholders involved in the project. The objective of this partnering is to develop an improved final design by proactively addressing major issues before they become a problem and identifying essential elements of the project's design that are to be maintained to preserve the project's commitment to sensitive environmental features associated with a project. Several different resource agencies may be involved in project partnering process. However, input from resource agencies are typically limited to only those areas associated with their purview. Resource agencies not authorized to complete regulatory approvals may be involved in the project partnering process but are limited to provide only guidance or recommendations. During the partnering process effective communication is essential to allow the team to respond quickly to unforeseen issues. Thus, by implementing a partnering approach and using the expertise of the various project partners, it is the intent that many or most of the construction issues associated with a project can be resolved in the design phase of the project instead of during construction. See Publication 10C, Design Manual, Part 1C, Transportation Engineering Procedures, for more information on this topic. F. Design-Build Projects. A design-build project is different than a design-bid-build project and may offer more opportunities for cooperation between the designer and the successful contractor to build the project. With a designbid-build project, the design process is completed under a separate contract and by a different entity than the 19-5

6 organization contracted to construct the project. An important component of the drainage design is the environmental approval process for it is this process that establishes where and when drainage features and hydraulic structures may be constructed and how they are to function. Normally, in the design-bid-build project, the designer is responsible for obtaining all regulatory clearances and environmental approvals for a project before a contractor is selected to build the project. Therefore, the design-bid-build process offers the contractor no input into the drainage design and commitments to regulatory agencies on how the project is going to be constructed. Only after the design is complete and the contractor's bid is accepted and awarded is the contractor able to comment on the design. As the permits and regulatory approvals have already been obtained as part of the design process prior to awarding the construction contract, the contractor is unable to make adjustments to the location, size, function of drainage features or methods of access to construct in-stream hydraulic structures without amending the permit and obtaining approval from the regulatory agencies. The process of amending the permits can be lengthy and create construction delays or can result in fines and additional delays if the contractor makes adjustments without obtaining the necessary regulatory approvals. With the design-build process, both design and construction functions are completed under a single contract. In this type of project, the contractor is included on the project team at the beginning of the design phase. The advantage to the construction contractor with the design-build process is that the contractor can provide insight into the design process upfront instead of addressing construction related issues associated with the drainage design and hydraulic features of a project after the job is awarded to the contractor. Not all design-build contracts involve the same design components. Typically PennDOT obtains the environmental clearance for this type of project and depending on the size and scope of the project they may obtain the necessary regulatory permits as well. In this type of situation the design-build team is often left with fewer design options as PennDOT has already accepted certain commitments as part of obtaining the environmental clearance and regulatory permits. For projects where PennDOT does not obtain the regulatory permits this task is often assigned to the design-build team that is awarded the contract. As the design and construction is completed under a single contract in a design build project, the contractor and their design partners are responsible to obtain all regulatory permits. The advantage of this type of project to the design-build team is that the construction contractor is able to provide input on how various elements of the design are going to be constructed and correspondingly to the environmental obligations committed to as part of obtaining the regulatory permits. This is a logical approach for many projects as the contractor will ultimately be responsible for constructing the various elements of the design that are needed to obtain regulatory approvals. Design-build projects typically have shorter schedules than their design-bid-build counterparts and are best used for projects that have well defined goals and objectives which can benefit from a compressed schedule. See Publication 448, Innovative Bidding Toolkit, for more information on the design-build process TECHNICAL ANALYSES FOR CONSTRUCTION OPERATIONS A. Introduction. Construction and maintenance of highways may require knowledge of low-flow discharge characteristics (e.g., discharges, flow stages, flow durations) to construct portions of a project in or near an existing stream, water body or floodplain. For example, the construction of a culvert or a bridge may require knowledge of seasonal fluctuations in flows to determine when stream elevations are below certain stages or below certain magnitudes. This knowledge may be useful in scheduling construction or designing temporary construction facilities to facilitate work within a channel or floodplain. For most facilities, completing construction is difficult if the work area is unavailable for prolonged periods of time due to the presence of water. Therefore, it is often necessary to facilitate construction by providing a means of temporary conveyance for the low flows through a project area. The methods of creating the temporary conveyance of low flows during construction operations can be completed in many different manners. However, scheduling such work to avoid flood seasons is especially important whenever any type of obstruction is needed in a floodplain or temporary reduction in stream conveyance is necessary to construct a bridge, culvert, drainage system or channel realignment. B. Timing and Risk. USGS publishes water resources data for gauged streams throughout Pennsylvania and the United States, tabulating mean daily discharges and other streamflow data based on actual stream measurements at stream gauges. These records can be very useful in determining the type and extent of temporary measures needed to construct proposed features in and around surface waters. Based on these daily records, a low-flow analysis can be used to determine an acceptable discharge for the hydraulic design of temporary conveyance features to facilitate the construction of proposed facilities within a stream or floodplain. 19-6

7 Typically, a rigorous flood frequency analysis is not required to determine the type of controls necessary to accommodate low flows through a construction zone. Using the aforementioned USGS data, mean daily flow discharges may be quickly examined to determine a range of typical daily stream discharges the contractor may anticipate encountering based upon the time of the year the work is projected to be completed. Normally, the larger the period of record (years of data) the more confidence can be placed in the analysis, and depending on the construction timing and the type of work, an appropriate low flow can be selected based upon an acceptable degree of risk. Data for the monthly mean discharges for stream gauges in Pennsylvania may be obtained from the USGS via the National Water Information System: Web Interface on the internet. For an explanation of how to transpose stream gauge data from a gauge to a construction area see Chapter 7, Hydrology. Transposed mean daily flows from stream gauges and rating tables based on the channel and floodplain geometry at the crossing site are useful for the design of temporary methods of conveyance, the proper scheduling of the time of year to complete the work and in selecting the location of work and material storage areas. In the event a stream gauge is not located near the stream crossing site, records from upstream or downstream gauges may be used with care to provide an indication of the usual magnitude, duration and timing flooding events. In the absence of stream gauge data, Chapter 7, Hydrology, contains a thorough presentation of various hydrologic methods that may be used as part of the hydrologic analysis for streams and waterways. Publication 13M, Design Manual, Part 2, Highway Design, Chapter 10 also contains information on different methods of establishing hydrology for a project. If hydrographs or other hydrologic data are furnished to the contractor or included in the plans for the contractor's use in planning and scheduling operations, the contract documents should indicate that the plots or data are for information only, and PennDOT assumes no responsibility for the conclusions or interpretations made from the records. C. Temporary Conveyance. Construction of temporary causeways, stream crossings and cofferdams necessary for the construction of bridges, culverts and stream realignments is the responsibility of the contractor. However, the responsibility for design and permitting of these structures varies depending on the type of contract. PennDOT is ultimately responsible for a project's environmental clearance and satisfactorily achieving and maintaining the commitments made to regulatory agencies as part of obtaining the project's permits. However, in many design-build projects, the design-build team is primary agent responsible for carrying out the design, permitting and implementation of the temporary staging on behalf of PennDOT. Conversely, with design-bid-build projects, PennDOT is responsible for the design and obtainment of all permits for temporary causeways and crossings. Ordinarily, these temporary features are designed to minimize or mitigate the adverse effects of the work conducted in the stream on the stream environment. The design of such features is necessary to secure permits from regulatory agencies and reduce the risk assumed by the contractor and thereby reduce construction costs. The primary regulatory agency responsible for reviewing and issuing waterway permits for temporary causeways and crossings is the Pennsylvania Department of Environmental Protection. Other agencies with regulatory authority over temporary activities in the waterway include the United States Army Corps of Engineers, United States Coast Guard, Federal Emergency Management Agency, and Pennsylvania Fish and Boat Commission. Stream crossings, causeways, and cofferdams to complete work within a channel or floodplain are normally designed to much lesser standards than permanent crossings. The criteria used for the hydraulic design of stream temporary conveyance features should be based on risk factors associated with the probability of flood exceedance during the anticipated service life (construction period); the risk to life and property; and traffic service requirements. Design standards for temporary crossings are discussed in Publication 13M, Design Manual, Part 2, Highway Design, Chapter 18 and Publication 15M, Design Manual, Part 4, Structures, Chapter 5. Detour stream crossings should accommodate floods larger than the event for which they are designed to avoid undue liability for damages from excessive backwater and to reduce the probability of losing the detour stream crossing structure during a larger flood. In most instances, the conveyance of floods larger than the detour design flood is provided for by a low roadway profile that allows overflow without creating excessive velocities or backwater. Design Example for Risk of Exceedance: A two-span bridge is scheduled to be replaced and a causeway is necessary to provide access for the contractor to remove the existing pier and construct the new pier. If the instream work is anticipated to take four months (0.333 years) to complete and the causeway is designed to be just above the seasonal normal water surface elevation but below the 2-year water surface elevation, what is the probability that a 2-year event will occur during the construction when the channel is partially obstructed? 19-7

8 The probability (p) of a 2-year event occurring in any given year is 1/return period (F) or 1/2=0.5. Thus, there is a 50% chance of the 2-year event occurring in any given year. The probability of an (F) year event in (n) years is equal to P=1-(1-1/F) n or 1-(1-0.5) =0.21 Therefore, there is a 21% chance of a 2-year event occurring during the construction period. More information on risk and exceedance is provided in Chapter 7, Hydrology. D. Erosion Control. The concerns of erosion and sediment pollution, where they might occur and how to control them, should be considered, at least in broad terms, during the early phases of the project scoping. All projects involving earth disturbance require erosion and sediment pollution controls. For small projects, this may be as simple as a section of silt fence or inlet protection. However, for larger more complicated projects, this may involve complex sequencing of operations and any number of a variety of erosion and sediment pollution controls. Chapter 12, Erosion and Sediment Pollution Control, presents an array of erosion and sediment pollution control best management practices available for use during the construction to control sediment transport and erosion. For simple projects, the information contained in Publication 72M, Roadway Construction Standards, and in Publication 408, Specifications, provides sufficient description of the controls to enable the contractor to construct them. However, for more complex projects, detailed plans, specifications and special provisions are necessary to indicate to the contractor how to construct the controls and what materials may be used for the construction of the temporary controls. As part of the design process, all erosion and sediment control considerations need to be thoroughly documented on the plans and in the specifications and special provisions provided to the contractor. The erosion and sediment control considerations specified on the plans and in the specifications are considered the minimum controls that are reasonably necessary to construct the proposed improvements. Although additional work or provisions may be needed to complete the construction based upon unforeseen conditions encountered in the field, the information contained on the plans and the specifications is to consider, evaluate and address all probable events the contractor may likely experience during construction. PennDOT's representative overseeing construction and his inspection staff use these documents to become knowledgeable about potential sources of erosion and sediment pollution in sensitive areas of the project and to become familiar with the control measures intended to minimize erosion, control sediment transport, and protect the environment during construction. It is very important that the information contained in the construction documents be discussed with the contractor before sensitive operations begin to be certain the contractor understands the function and importance of the controls and that the specified controls are properly included in the formulation of the work plan. The contract documents are also used by the project's inspection staff to conduct periodic field observations and inspections of the proposed controls to assess their effectiveness, correct deficiencies and improve control procedures throughout the construction phase. Regular inspection of installed controls during construction is essential for effective erosion and sediment control. Regulatory agencies issuing environmental clearance for projects periodically inspect the construction and use the plans to determine if the contractor is conforming to the stipulations of the permit by constructing the controls specified in the permit. If deficiencies in the design or performance of control measures are discovered, the contractor can be directed by the regulatory agencies to take immediate steps to correct the problem. When observed deficiencies in the erosion and sediment pollution control plan are considered complex or have the potential to create significant consequences, the contractor is to contact PennDOT's Project Manager, to determine if consultation with the designer is warranted to correct the potential problem. Therefore, thorough documentation of the erosion and sediment pollution controls on the plans and other construction documents is essential. E. Sequence of Operations. The time of the year and total construction time should be considered when developing a sequence of operations for a project whenever work is proposed in close proximity to a water resource. Certain elements such as construction of embankments along a stream or working in a floodplain should be completed before the anticipated flood season. In some areas, work cannot be performed in the streams during certain times of the year such as times when fish spawning occurs or migratory fish populations are present. In other areas, the stream or surface water body may have other functional values that need protection. Other functional values of water resources include water supply, irrigation, recreational use, flood control, wildlife habitat, 19-8

9 groundwater recharge and commercial use. During certain periods of the year, flows to certain water resources may be more sensitive to alterations in flow, and careful consideration should be given whenever work is proposed in a stream, waterway or floodplain. As noted in Chapter 12, Erosion and Sediment Pollution Control, PA Code Title 25, Chapter 102 requires all projects requiring an NPDES permit to develop a narrative as part of the project's erosion and sediment pollution control plan. The plan is to contain a sequence of operations, prepared by the design engineer, to control erosion and minimize sediment pollution during construction. Typically, the contractor uses the construction sequence prepared by the design engineer to form the basis of their construction operations. This sequence allows the contractor to plan ahead and control erosion and sediment transport before it becomes a problem rather than adding measures after damages have occurred. If the contractor determines a change in the approved sequence of operations is warranted after the design sequence is completed and the NPDES permit is issued for the project, the contractor is responsible for notifying the PA DEP and County Conservation District of the changes and if necessary, obtaining the appropriate amendments to the permit. If the contractor changes the sequence of operations, all erosion and sedimentation controls required for a given sequence are to be in place prior to commencing earth disturbance activities. There are many construction-related hydraulic complications related to construction scheduling. Although these problems are studied in detail during the design phase, they should be initially considered, at least in a preliminary manner, as early as possible. Commitments regarding water resource related items made in the Environmental Documentation (i.e. Environmental Impact Statement (EIS), Categorical Exclusion Evaluation (CEE), Environmental Assessment (EA)), are to be made known to the personnel who are involved in the actual construction. Some commitments that appear reasonable upon cursory examination of the issues associated with a project may not be feasible to build. In other cases, construction occurs so long after the Environmental Documentation has been prepared that those commitments are forgotten or not included in the plans or contract documents. PennDOT has developed the Environmental Compliance Tracking and Management Systems (ECTMS) to track compliance with commitments made to the regulatory agency through the design, construction and maintenance phases of the project to ensure the commitments made to the agencies are being followed through in subsequent phases of the project. For more information pertaining to the tracking of environmental commitments for PennDOT projects, refer to Publication 10X, Design Manual, Part 1X, Appendices to Design Manuals 1, 1A, 1B, and 1C, Appendix T. F. Other. Construction activities adjacent to large lakes or reservoirs, areas subject to tidal fluctuations, and waterways where wave action may be a concern (i.e. navigable waterways) all present unique problems that need to be carefully considered on an individual basis during the design. Frequent or large fluctuations in the water levels may require special construction techniques such as dewatering or underwater work in these areas to complete construction and maintain the use of the water resource during construction operations. In other locations unique geologic conditions may exist that require special considerations to safely and responsibly complete construction activities without causing damage to the environment (i.e. areas containing karst geology (areas susceptible to sinkhole formation because of the existing natural carbonate geology), mine areas, and acid rock environments, etc.). Other issues such as access to the site, on-site storage of construction materials, time of year restrictions and sequence of constructions may also warrant special considerations at these sites DESIGN OF BRIDGES A. Bridge Considerations. Any special hydraulic considerations or other special provisions related to the phasing of bridge construction need to be specified on the plans, such as special erosion and sediment pollution controls or unique considerations needed to manage exiting streamflow or stormwater drainage during construction. Regardless of which entity (PennDOT or the contractor) is responsible for the development of the temporary phasing and obtainment of the permits to facilitate construction, hydraulic considerations during construction usually differ from the design considerations for the completed facility. For construction staging, it is important to provide access to the contractor so that the various elements of the bridge design can be constructed while maintaining conveyance in the stream and floodplain. Typically, most bridge work requires some activities either in the stream or at the very least in the floodplain. Although there is some flexibility with the selection of an appropriate design storm to facilitate temporary conveyance through the work zone during construction, in most cases the design event is typically no less than the 19-9

10 2.33-year event. In some cases such as large streams and rivers, the 2.33-year event is somewhat large and cannot easily be accommodated when large watersheds are involved. In these cases, it may be acceptable to use an event that is less than the 2.33-year event to design temporary means of conveyance if it can be supported by stream gauge data, time of year restrictions and an appropriate level of risk for the situation. When a temporary bridge is required for a project to keep the crossing open to the public, the standard design storm is the 10-year storm. However, the design storm may be decreased to a lesser event if the situation warrants a smaller flow, but the design flow is not to be less than the 2.33-year event if the bridge is to remain open to traffic. For further discussion on the topic of temporary bridges, see Publication 13M, Design Manual, Part 2, Highway Design, Chapter 18, and Publication 15M, Design Manual, Part 4, Structures, Chapter 5. B. Foundation and Scour. As part of the design and counter measures proposed and analyzed to protect the structures, evaluate any site conditions that may impact the foundation design or create unusual scour problems. Consideration should be given not only to the effects of scour on the permanent structure but also the effects of the temporary staging used to construct the proposed improvements may have upon scour. Cofferdams, falsework and occasionally contractor's equipment (e.g., barges) constrict the stream channel more than the completed substructure and consequently have greater potential for causing scour, bank caving and debris collection. If specific elements of the bridge design are dependent upon special foundation or scour considerations, it is imperative that the contract documents be prepared so that individuals responsible for constructing and inspecting the proposed improvements are sufficiently informed of conditions used in the design and analysis. This is important so that individuals completing the construction can identify possible problems when conditions are different than shown on the contract documents and evaluated in the design. For additional information on scour and foundation design, refer to Chapter 10, Bridges, Publication 15M, Design Manual, Part 4, Structures, Chapter 7 or Hydraulic Engineering Circular No. 18. C. Environmental Aspects. Minimal disturbance of the banks and bed of a stream during the construction period typically reduces erosion damage to the banks and sedimentation in the stream thus reducing the risk of harm to fish and wildlife. Embankments in or along streams should be constructed of erosion-resistant material and/or protected against erosion to avoid adverse sediment concentrations that contribute to the turbidity of the stream and potentially affect the normal depth of water in the stream. In-stream operations associated with bridge construction, such as the construction of a pier or abutment or use of cofferdams, crossings and causeways that could potentially cause increases in turbidity during the spawning season should be avoided to prevent potential adverse environmental effects from the proposed work. Detours and construction roads are other potential sources of turbidity that should be either constructed at a time that fishery activity is low, or when special protection measures are proposed to control any harmful effects of the construction associated with erosion. Silts and clays generally flush out of the substrate over a period of time, but sands tend to become embedded. Gravel and rock, similar to the gradations found in the existing substrate typically do the least damage to the aquatic habitat. The Pennsylvania Fish and Boat Commission should be contacted to obtain information on the presence of fish at a specific location and any seasonal restrictions to work in or around streams. Pumping of water from inside cofferdams and other dewatering operations may have a discharge of unacceptable quality to the receiving stream. Mitigation measures, such as settling basins, may be necessary if the ecosystem of the stream could potentially be impaired by the temporary degradation of water quality. D. Stream Restoration. Bridge construction projects often include extensive work in the stream including construction of temporary roadways, temporary bridges, access roads, crane pads and channel relocations. As part of the design process, consider if any special precautions are needed by the contractor to protect the stream from pollution caused by fuels, oils, bitumen, calcium chloride or other harmful materials during construction operations. Upon completion of the construction work in areas around the bridges that are not stabilized with scour protection measures or other bridge appurtenances, the contractor is to be directed on how to repair all portions of the stream that received damage or were affected by the construction activities. The stream should be restored to its preconstruction condition as reasonably practicable, restoring scour holes and removing all foreign material from the stream used in the construction process

11 19.5 DESIGN OF CULVERTS A. Preparation. It is essential that the design of any culvert takes into consideration how the construction of a culvert impacts the existing conveyance at a site during construction, and the contract documents developed to accurately describe the existing, proposed and temporary conditions the contractor is anticipated to experience during the construction of the culvert. Prior to construction of any culvert or hydraulic structure, the plans, specifications and other construction documents developed by the designer are to be thoroughly reviewed by the contractor and inspection staff to be certain that the design accurately considers and accommodates current site conditions. If the field conditions are not consistent with the conditions used for the design, the contractor is to contact PennDOT and PennDOT may require a revised culvert design. B. Installation. Fabrication, bedding, assembly, backfill and scour protection are as important to culvert service as the hydraulic and structural design. Without proper construction, both the performance and the service life of the culvert can be seriously lessened. Therefore, development of proper documentation describing how to construct all facets of a culvert is essential in the design phase of the project. As the pipe performance is contingent upon site conditions it is important to select the appropriate pipe based upon the specific constraints of the installation site. Publication 13M, Design Manual, Part 2, Highway Design, Chapter 10, Appendix B contains valuable information to aid in the selection of the appropriate pipe material such as, service life, standard pipe sizes and minimum and maximum acceptable fill heights. Depending on the type of use PennDOT may require alternate pipe designs. Publication 13M, Design Manual, Part 2, Highway Design, Chapter 10, contains valuable information describing the process and factors to be considered when selecting the appropriate alternate pipe designs. Precast concrete box culverts can be constructed to virtually any dimension needed with the size limited only by what can be physically transported to the site. It is important to note that many local roads and state roads with fourdigit road numbers cannot support heavy loads and therefore may not be accessible for very large precast pipes. Regardless of their location, all applicable box culverts are to be designed in accordance with Appendix 9A, Joint Agency Guidance for the Analysis of Environmental Impacts and Other Issues for Short Span Structures. Unlike concrete box culverts both concrete elliptical pipes and concrete arches come in standard pipe sizes. For standard installation details such as pipe bedding, backfill requirements and end treatments refer to Publication 72M, Roadway Construction Standards. Regardless of their location, material or geometrics culverts should be protected from damage during construction operations and should be inspected throughout the construction phase of the project. A particularly critical time for inspection is after the installation of the culvert and prior to backfilling. Another critical time for inspection is upon completion of grading operations and prior to the start of surfacing operations. The need for proper inspection is not contingent upon culvert location. It is as important to inspect culverts that are not under the roadway as it is for those structures that are under the roadway. Prior to the acceptance of the installation, all culverts should be inspected and cleaned as necessary. C. Stream Restoration. The installation, replacement or extension of a culvert typically requires minor amounts of channel work. The contract documents are to direct the contractor to take sufficient measures to minimize damage to the stream and only work in portions of the stream that are specified and permitted by the regulatory approval process. Upon completion of the construction activities, the stream or channel is to be restored to its preconstruction condition as reasonably practicable. Any area of the stream outside of the construction limits that may have inadvertently been damaged either directly or indirectly by construction activities is to be restored or repaired by the contractor DESIGN OF OPEN CHANNELS A. Introduction. Many of the construction considerations for open channels are the same as for culverts and bridges. Thus, Sections 19.5 and 19.6 should be reviewed as they relate to open channel construction. The following sections concentrate on those construction considerations that are unique to open channels. In designing a permanent or temporary modification of a stream/channel, the designer needs to consider the following: 19-11