We assessed the potential impacts of increased river flooding from climate change on bridges in the continental United States. Daily precipitation statistics from four climate models and three greenhouse gas (GHG) emissions scenarios (A2, A1B, and B1) were used to capture a range of potential changes in climate. Using changes in maximum daily precipitation, we estimated changes to the peak flow rates for the 100-year return period for 2,097 watersheds. These estimates were then combined with information from the National Bridge Inventory database to estimate changes to bridge scour vulnerability. The results indicate that there may be significant potential risks to bridges in the United States from increased precipitation intensities. Approximately 129,000 bridges were found to be currently deficient. Tens of thousands to more than 100,000 bridges could be vulnerable to increased river flows. Results by region vary considerably. In general, more bridges in eastern areas are vulnerable than those in western areas. The highest GHG emissions scenarios result in the largest number of bridges being at risk. The costs of adapting vulnerable bridges to avoid increased damage associated with climate change vary from approximately $140 to $250 billion through the 21st century. If these costs were spread out evenly over the century, the annual costs would be several billion dollars. The costs of protecting the bridges against climate change risks could be reduced by approximately 30% if existing deficient bridges are improved with riprap.

AbstractConversion of a natural watershed into its equivalent kinematic wave rectangular plane has long been a concern in the practice of storm water numerical simulations. Based on the principles of mass and energy, the actual watershed and its virtual kinematic wave plane can be related by the watershed shape factor that involves the waterway length and slope and watershed area. In this study, two dimensionless watershed shape functions are derived to use parabolic function and trigonometric sine curve for watershed conversion. These two watershed shape functions produce good agreements with the maximum overland flow length method for hypothetical square watersheds. Also, these two watershed shape functions are able to reproduce similar kinematic wave plane widths as reported in a calibrated model. Furthermore, in this study, these two watershed shape functions are tested by nine observed rainfall events and three levels of modeling details. These 54 case studies reveal that the parabolic shape function...

Mozambique, like many African countries, is already highly susceptible to climate variability and extreme weather events. Climate change threatens to heighten this vulnerability. In order to evaluate potential impacts and adaptation options for Mozambique, we develop an integrated modeling framework that translates atmospheric changes from general circulation model projections into biophysical outcomes via detailed hydrologic, crop, hydropower and infrastructure models. These sector models simulate a historical baseline and four extreme climate change scenarios. Sector results are then passed down to a dynamic computable general equilibrium model, which is used to estimate economy-wide impacts on national welfare, as well as the total cost of damages caused by climate change. Potential damages without changes in policy are significant; our discounted estimates range from US$ 2.3 to US $7.4 billion during 2003-2050. Our analysis identifies improved road design and agricultural sector investments as key 'no-regret' adaptation measures, alongside intensified efforts to develop a more flexible and resilient society. Our findings also support the need for cooperative river basin management and the regional coordination of adaptation strategies.

Defining collection system performance criteria is a critical step in the master planning process because it sets the metrics by which existing collection system infrastructure will be evaluated to meet level-of-service goals by which future facilities will be designed. It is important to recognize the difference between planning criteria and design criteria for judging the performance of collection system infrastructure. Planning criteria relate to those metrics that are used to analyze the adequacy of existing facilities and to project future infrastructure needs for financial planning purposes. These criteria are not intended to provide the same expected levels of safety and protection that design criteria provide. It is generally inappropriate to use standard design criteria as planning criteria, especially when significant wet weather flows impact an existing collection system (as is the case with an aged combined sewer system). For example, new sewers are designed to convey flow under non-surcharged conditions, while surcharging may be permissible during the analysis of existing sewers, especially during wet weather flows. Wet weather flow may dramatically affect the performance of collection systems. Master planning collection system infrastructure requires an assessment of the performance criteria used to size the systems during wet weather flows. Determining how to measure the performance of existing facilities and deciding on a design event or condition, or level of service, for wet weather planning may not be straightforward. This is especially true when basing the performance on an expected flow duration series. Literature and regulations offer little guidance on the design condition or design flow event frequency to use. Choosing a large event can incur significant capital costs, while too small of an event may lead to unacceptable overflow frequency and volume. This paper examines collection system performance criteria for both planning and design purposes that can be used for completing modeling analyses and identifying capital improvements. The planning and design criteria help define the type, location, and extent of the facility deficiencies that should be corrected to maintain service reliability. Criteria for dry weather flow as well as wet weather flow conditions caused by infiltration and inflow are included. Examples are included to illustrate how results can vary from one approach to another, and affect the extent of capital improvements as well as the level service of the collection system.

The goal of risk management is to minimize expected costs over time where the costs are defined in some probabilistic fashion. Traditionally, total expected costs due to failure are summed for planning purposes over a meaningful spatial and temporal domain and assigned a weight based on the likelihood of occurrence. Expected costs are the product of the consequence of an event (e.g. failure) and the probability of the event occurring. This is the commonly applied definition of infrastructure risk; Risk = criticality x vulnerability. The total risk-based cost is then compared with expected life-cycle costs to take mitigation action to reduce risk. Actions may include insurance, inspection, monitoring, improved construction, or increased maintenance. Action is taken if the benefits in terms of avoided costs exceed the costs associated with risk reduction. Unfortunately the probability of occurrence of specific events is uncertain at best, and at worst the decision-maker is in total ignorance about the likelihood of an event occurring. In the face of uncertainty with respect to the probability of these events, guidance for prioritization of projects may be gained from ideas developed in portfolio investment theory, which is concerned with decision making under uncertainty. Common methods of benefit/cost-based decision criteria fail to account for uncertainty. An example risk-based calculation from the sanitary sewer field will be used to illustrate risk management at the planning level for pipeline rehabilitation projects using risk based decision criteria.

Zone 7 is a treated water wholesaler in California, providing service to approximately 190,000 customers in the cities of Livermore, Pleasanton and Dublin. Zone 7 facilities include two treatment plants and 32 miles (51.5 km) of transmission pipeline. The current maximum daily demand is 74.36 MGD (3258 l/s) delivered to 36 customer turn-outs ranging in maximum daily demand from 7 to 5,200 GPM (0.44 to 328 l/s). An Asset Management Study was conducted to assess future expenditures required to meet level-of-service requirements for water delivery. As part of this assessment, the vulnerability, or likelihood of failure, was estimated along with criticality, or consequence of failure. This analysis was designed to highlight transmission system elements that were most likely to cause level-of-service failures. WinPipes, an EPANET based water distribution system solver and output interpreter was used to evaluate the consequence to the level-of-service associated with pipe failure. The fraction of demand not met during a pipe break event was used as a measure of criticality of the pipe to the system performance. The simultaneous failure of two pipes was also evaluated to account for catastrophic earthquake induced failure. The results of the criticality analysis were used to prioritize future inspection, maintenance, and replacement tasks.

The long-term management of wet-weather SSOs may involve some combination of increased capacity of conveyance, storage, and treatment systems along with flow reduction through collection system rehabilitation. The amount of flow reduction attained by rehabilitation has been difficult to predict during project planning phases because many unknown variables affect rehabilitation performance. Post-auditing of rehabilitation efforts has shown widely varying results. Rehabilitation as an SSO control does show promise as part of a long-term management plan, especially when the long-term rehabilitation strategies may be revised based on interim, mid-project performance data. However this form of adaptive management plan may not be amenable to short-term performance goals that must be met to avoid permit violations and subsequent enforcement actions. The trade-offs between short-term permit enforcement, reliability of the management plan and long-term level-of-service performance goals must be balanced in a cost-effective manner. Centralized, downstream storage and treatment controls tend to be more reliable solutions for meeting SSO goals and permit requirements in the short term because they are more controlled and the effect of these controls on the wet-weather response hydrograph is well understood. Rehabilitation is a decentralized solution and it is difficult to predict performance for SSO management through RDII reduction. However, when the problem is approached from a long-term perspective, that of an infrastructure maintenance problem, rehabilitation becomes more attractive. It is likely that persistent maintenance efforts that are fine-tuned by adaptive management strategies based on measured performance data will pay off in a cost effective manner over the life cycle of the infrastructure. This is because pipes that are deteriorated and leak RDII into the system will eventually fail structurally and will require repair or replacement to maintain service. This expense will occur regardless of the downstream SSO controls that are installed. The time frame for meeting performance goals becomes a critical factor in SSO management decision-making. In the long-term, it may be approached as an asset management problem, minimizing the life-cycle costs while meeting a level of service that prevents SSOs to some defined frequency. In the short term the variability.

ESTIMATING THE CONDITION OF UNINSPECTED SEWER PIPELINESThe quantity and quality of information that owners of collection systems in the U.S. are currently collecting come in the wake of a long history of less-than-complete record keeping for pipeline maintenance, condition assessment and rehabilitation efforts. Business models of collection system planning and operation such as asset management techniques are proving the value of high-quality...Author(s)Len WrightShawn DentRolf OhlemutzSourceProceedings of the Water Environment FederationSubjectSession 3: Dynamic Rehabilitation ProjectsDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2004ISSN1938-6478SICI1938-6478(20040101)2004:5L.162;1-DOI10.2175/193864704784107047Volume / Issue2004 / 5Content sourceCollection Systems ConferenceFirst / last page(s)162 - 178Copyright2004Word count499

Detailed flow and rainfall measurements, accompanied by long-term simulation, were used to identify the inflow and infiltration response characteristics of the sanitary sewer collection system in Vallejo CA. This response has produced sanitary sewer overflows on numerous occasions throughout various locations in the collection system. A mix of collection system rehabilitation, capacity upgrades, storage and increased treatment capacity may be used to control future wet-weather flows to a regulatory standard. A major limitation to optimizing the design of these wet-weather controls is a relatively high uncertainty regarding the effectiveness of collection system rehabilitation to control wet-weather flows. The ability of collection system rehabilitation activities to control wet-weather flows will in turn affect the performance of all downstream controls, including conveyance, storage and treatment. If rehabilitation effectiveness is over-estimated, overall control performance will not meet design standards, and if underestimated, significant over-expenditure of resources is possible. A risk-based approach was used to identify the importance of rehabilitation effectiveness on the overall design. Probability density functions of wet-weather pollutant control for storage, treatment and rehabilitation were derived from direct observations and used to estimate the overall reliability of various mixes of design alternatives. Based on this analysis, a concentrated small-scale rehabilitation project was used to reduce the uncertainty associated with estimating the performance of rehabilitation for sanitary sewer overflow (SSO) control.