Water System Service Categories, Post-Earthquake Interaction, and Restoration Strategies

Transcription

1 OPINION PAPER Water System Service Categories, Post-Earthquake Interaction, and Restoration Strategies Craig A. Davis a) M.EERI This paper illustrates the relation between resilience and water system serviceability, and the dependence of community resilience on water system resilience. Five normally provided water system service categories are defined: water delivery, quality, quantity, fire protection, and functionality. Water system performances are described in terms of how these services are provided to customers after an earthquake in relation to pre-earthquake services. The important distinction between system operability and functionality is defined. The characteristics of each service restoration and how they interact are explained. A case study from the Los Angeles Water System is presented to show applicability of the five service categories in actual post-earthquake restorations. The examined service restoration features can be used as engineering and management principles to improve overall service restoration. Some strategies for improving postearthquake services and their restorations are presented in the context of the five service categories. Reviewing the five water service categories identifies how water system resilience is more complex than previously recognized. [DOI: /022912EQS058M] INTRODUCTION Water systems are large and complicated geographically distributed systems traversing many geologic formations and hazards and can experience damage and resulting service losses when subjected to a widespread shock from an earthquake. A water system s seismic resilience is dependent upon the amount of service losses sustained by an earthquake and the time required to return the services. The seismic performance of water systems is critical to the resilience of the communities they serve. The assessment of water system resilience and its impact on community resilience requires an understanding of: (1) the water system s geographic distribution, operational capabilities, and resources; (2) the earthquake hazard geographic distribution; (3) the geospatial impacts of the earthquake hazards on the water system; (4) potential secondary damages; (5) the emergency response and recovery activities; (6) the water system serviceability following the earthquake event; and (7) the system restoration. These topics have been researched in the past (e.g., Wang 2006, Shi 2006, Brink 2009, Chang and Shinozuka 2004); however, past research on water system a) Los Angeles Department of Water and Power, 111 N. Hope Street, Room 1356, Los Angles, CA, Earthquake Spectra, Volume 30, No. 4, pages , November 2014; 2014, Earthquake Engineering Research Institute

2 1488 C. A. DAVIS serviceability and restoration focused on a system s ability to deliver some level of water flow to the service connections without regard to the volume, pressure, quality, or reliability of the water service. Some, but not all, categories of water system serviceability have been covered in practice in relation to performance objectives (e.g., Ballantyne 1994, Eidinger and Avila 1999). Neglecting the provision for volume, pressure, quality, or reliability leaves a significant gap in the understanding of water system performance and serviceability following an earthquake. This paper focuses on the above item (6), post-earthquake water system serviceability, and the associated aspects of other items. In order to assess a water system s serviceability following an earthquake and how it impacts community resilience one must first understand: (a) the service types or categories a water system needs to provide after a disastrous event (i.e., services customers are dependent and reliant upon for personal and community wide survival and sustainability); (b) how the service categories interact in positive and negative ways during the post-event response and restoration periods and the respective importance each service has on community recovery; and (c) the acceptable objectives or performance levels for each service category. This paper concentrates on items (a) and (b); item (c) has previously been addressed by others (e.g., Ballantyne 1994, Eidinger and Avila 1999, Ballantyne and Crouse 1997, ALA 2005). Even though there is a need for improving the development of performance objectives in relation to the service categories described herein, this topic is not addressed due to the need for further study to properly identify how each water service category restoration time interrelates with community resilience, which is beyond the scope of this work. Davis and O Rourke (2011) originally defined five normally provided water service categories (in terms of restoration objectives) and Davis (2011) presented an initial characterization of the water delivery, quality, quantity, fire protection, and functionality service categories helpful for strategizing post-earthquake restorations. This paper expands and further develops the concepts of Davis (2011) by first explaining water system performance and service categories, then some service category characteristics, followed by a case study showing category applicability to a real water system. The service category interactions are described and related to some restoration strategies. Lastly, the relation between water system services and community resilience is identified. Viewing water systems in the context of the five service categories allows one to comprehend water system performance from a much broader perspective and also to understand how water system resilience is more complex than previously recognized. The concepts on water system services presented herein aid in improving our understanding of water system resilience and its inter-relation with community resilience, and strengthen our capabilities for reducing seismic risks. WATER SYSTEM PERFORMANCE AND SERVICES Table 1 shows three primary water system seismic performance categories: water services, life safety, and property protection, not necessarily in any priority order (safety is always top priority). The water services category is made up of at least the five additional categories in Table 2, making a total of seven primary water system performance categories. The total number of water system seismic performance categories is not limited to seven. Several references (Chang and Shinozuka 2004, Ballantyne 1994, Eidinger and Avila 1999, Ballantyne and Crouse 1997, Bruneau et al. 2003) identify many other categories.

3 WATER SYSTEM SERVICE CATEGORIES, POST-EARTHQUAKE INTERACTION, AND RESTORATION STRATEGIES 1489 Table 1. Primary water system performance categories Performance category Description Water services Provision of water services identified in Table 2. Life safety Preventing injuries and casualties from direct or indirect damages to water system facilities; includes safety matters related to response and restoration activities. Property protection Preventing property damage as a result of damage to water system components; also includes preventing water system damage. However, it is believed the additional categories identified in these and possibly other references are subordinate and needed to achieve the primary water services presented in Table 2 because the main purpose for a water system is to provide safe and reliable water services to customers. Table 2 summarizes five service categories normally provided by water systems using common network components and topology. The provision of water services and the protection of life and property are arguably the most important performances a water system can achieve. Life safety can be threatened when, for example, water system structures fail, dangerous chemicals (e.g., chlorine) are released into the atmosphere, large volumes of water are catastrophically released into populated areas (e.g., dam or levee failure), and so on. Property damage can result from similar water system damages, as well as from water from pipe breaks. Proper seismic mitigations to critical components within a water system (e.g., strengthening dams, pipes, and other facilities, anchoring chemical containers, etc.) are important measures to prevent casualties and property damages. Although these mitigations are critical for life and property safety and aid in improving water system resilience, they generally focus on specific components within the system and, as a result, do not always directly improve the ability to provide post-earthquake water services. Water services include those aspects necessary to provide a safe and reliable water supply to the water system customers, as described in Table 2, including water delivery, quality, quantity, fire protection, and system functionality. A system or portion of system meeting the description in Table 2 for each category is considered restored to the customer service connection. The critical factors needed to achieve the service restorations noted in Table 2 identify the importance of all systemic aspects in a water system for achieving the different water services. The descriptions in Table 2 are intended to capture most aspects associated with modern water system services around the world; however, description modifications may be needed to suit certain regional practices. For example, water quality description needs slight modification to remove pressure requirement to fit Japanese regulations (Hirayama and Davis 2013). The following section describes the service category characteristics. The distinction between water delivery, quantity, quality, and fire protection services is relatively easy to understand. The difference between functionality services and the cumulative restoration of the other water services is not so inherent and is described in more detail here. Functionality services describe the ability of a system to reliably perform. System reliability is a measure of a system s consistency and dependability in an earthquake and performance is the system s ability to execute its intended operations. A highly functional system can achieve its basic purpose (i.e., provide water delivery, quality, quantity, and

4 1490 C. A. DAVIS Table 2. Water service categories and critical factors for restoring and providing services Service categories Description Critical factors Water delivery Quality Quantity Fire protection Functionality The system is able to distribute water to customer service connections, but water delivered may not meet quality standards (requires water purification notice), pre-event volumes (requires water rationing), fire flow requirements (impacting firefighting capabilities), or pre-event functionality (inhibiting system operations). The water quality at service connections meets pre-event standards. Potable water meets health standards (water purification notices removed), including minimum pressure requirements to ensure contaminants do not leach into the system. Water flow to customer service connections meets pre-event volumes (water rationing removed). The system is able to provide pressure and flow of a suitable magnitude and duration to fight fires (CBSC 2007). The system functions are performed at pre-event reliability, including pressure (operational constraints resulting from the earthquake are removed/resolved). Inspections and damage identification, isolating damaged portions of distribution network, using redundancies in transmission and distribution networks, available emergency water storage, materials and supplies (including sustenance for workers), crews including mutual aid and assistance, facility repairs (pipes, pump stations, storage, etc.), communications, transportation corridors, and power for repairs and operations. Treatment facility repairs, pipe repairs, disinfection, availability and transport of disinfectants, sewage and contaminant leaks/spills, laboratories for testing, coordination with health services regulators. Local emergency supplies, stability of tanks and reservoirs, repairing transmission pipes, repairing aqueducts, and similar factors as water delivery. Similar factors as water delivery and quantity restoration with spatial coverage consistent with fire fighting equipment. Designs, materials, and funds for permanent repairs, reconstructions, and/or alternative system modifications. fire protection services) prior to completing all water infrastructure repairs (Davis et al. 2012). Damage imposes constraints that do not allow the system to function with its preearthquake performance and reliability in advance of completing all necessary repairs, even when the other four services are completely recovered. After the water delivery, quality, quantity, and fire protection services reach 100% restoration, the system may be fully operational and able to completely service customers (herein, at this state, the system is termed operational and has operability) prior to the system being fully functional. The state of

5 WATER SYSTEM SERVICE CATEGORIES, POST-EARTHQUAKE INTERACTION, AND RESTORATION STRATEGIES 1491 complete operability is mostly from the customers perspective of having all services restored, but the system may not operate or function as it did prior to the earthquake. Full functionality services are not recovered until the constraints imposed by damages are removed or resolved by completing repairs, possible new construction, and/or operational modifications. A complete functionality recovery returns all services to their pre-earthquake performance, reliability, and redundancy level, at which time the system can operate or function as dependably as it did prior to the earthquake event. Thus, the functionality services are the last to be fully restored and may be completed after or along with some or all of the other services. This view of functionality is consistent with those normally considered for resilience modeling (e.g., Bruneau et al. 2003, Cimellaro et al. 2010), with the exception presented herein distinguishing the important difference between the system operability and functionality. For example, in the context of this article, Cimellaro et al. (2010) defines recovery time as the period necessary to restore water supply system functionality to a desired level that can operate or function the same, close to, or better than the original one (which is not achieved until all significant water system components are restored to pre-event conditions). Bruneau et al. (2003) identifies restoration as the time when the infrastructure is completely repaired. Restoring operability and functionality are two necessities to achieve resilience. Understanding the difference between water system operability and functionality is important to the application of water system services in supporting community resilience (operability recovery) and water system resilience (functionality recovery). Operability recovery is critical for community resilience and functionality recovery is critical for ensuring the community recovery is complete and sustainable. The difference in operability and functionality restoration and recovery times lies mostly in system redundancy and resourcefulness, which are dimensions of resilience (Bruneau et al. 2003). As previously described, operability is achieved through a combination of service restorations, but cannot by itself be described as a water service. The time it takes to obtain operability status throughout a system can only be viewed as the temporal sum to incrementally restore water delivery, quality, quantity, and fire protection services, and it therefore serves as a descriptive milestone delineating when customers resume receipt of their accustomed services. Thus, it is important to understand how to assess each service category and their respective characteristics. The ability of a water system to provide the service categories in Table 2 can be assessed at any given time as a ratio of the number of customers with the service after the earthquake to the number of customers having the service before the earthquake. An assessment can be performed in relation to a seismic evaluation or an actual event for each service category in Table 2. The number of customer services restored over time can be monitored to track and evaluate overall system serviceability for each category. Davis (2011) summarizes alternative methods for estimating service recovery if the number of service connections cannot be easily determined. CHARACTERISTICS OF WATER SERVICE RESTORATIONS Many times, the restoration of water service is assumed to meet only one category, which includes the provision of good water quality satisfying normal pre-earthquake demands. This

6 1492 C. A. DAVIS is implied to customers when practitioners and researchers make statements about water service restoration without clarifications regarding quality, quantity, or pressure impairments (e.g., Chang and Shinozuka 2004, Lund et al. 2005, Shi 2006, Wang 2006, Brink 2009, Bonneau and O Rourke 2009, Romero et al. 2010, Dueñas-Osorio and Kwasinski 2012, TCLEE 2015). In reality, water systems are not restored so precisely. Restoration comes in steps to each customer and throughout the supply, treatment, transmission, and distribution subsystems. In practice, water services are restored more closely to the categories presented in Table 2 (e.g., Davis et al. 2012). For water delivered through the infrastructure networks, water delivery is the first step in service restoration to the customer s service connection and is a prerequisite for meeting the quality and quantity services. The other service restoration categories may be accomplished in any order and possibly with water delivery restoration. The water delivery and functionality services bound the complete recovery time of the other services (i.e., the time services return to normal). All service restorations are made while holding high value to the life safety and property damage performance categories in Table 1. Figure 1 shows different restoration times for each water service category and a bounding operability curve. Some characteristics of each water service category, defined in Table 2, are described using Figure 1 as an example. The service restoration curves in Figure 1 do not represent the performance of any specific water system following any specific earthquake Normal Service Level Water Service (%) Earthquake Event Water Delivery Quality Quantity Functionality Operablity 20 Fire Protection 0-1 t Time (weeks) Figure 1. Example water service restoration curves. Refer to Table 2 for water service definitions. Operability is not a service; it is a milestone delineating collective restoration of water delivery, quality, quantity, and fire protection services.

7 WATER SYSTEM SERVICE CATEGORIES, POST-EARTHQUAKE INTERACTION, AND RESTORATION STRATEGIES 1493 scenario; the curves are only intended to aid in describing the service category characteristics. The units of weeks shown on the time axis are not intended to be typical. An earthquake impacting a water system occurs at time t 0. For the example in Figure 1, the water system has the ability to deliver water to about 60% of the customers immediately after the earthquake, and service continues to decline for a short time after the earthquake until about only 30% of customers have water delivered to their service connections. The immediate drop in service results from damage to water system facilities and components; the damage is severe enough to eliminate the ability to deliver water to about 40% of the customers. The continued decline in water delivery service results from water leaking through broken pipes, draining storage tanks and reservoirs, and reducing pressure in the network. The trend reverses as the damaged portion of system is contained by making repairs, isolating flow around the damage, using redundancies in the system, and applying available water sources into the portions of network which can still operate, even if some damage remains. The water delivery continues to increase as the network repairs continue. The network may be able to deliver water to all customers at a point when the pipe network is sufficiently repaired, but some leaks may still exist, and the pump stations, reservoirs, and other facilities are sufficiently operable to provide flow to all parts of the network. However, at this stage some portions of the network still may not be able to provide services meeting water quality, quantity, pressure, or reliability at the pre-earthquake levels. The water delivery restoration curve identifies the number of customers without water over time. These customers must obtain water for survival from alternate sources until the water network regains sufficient capability to provide potable supply. This water accessibility service may come in many different forms and is normally provided by water purveyors, emergency responders, and volunteers. This paper intends to focus on restoration of services provided through the water supply network and therefore does not describe water accessibility services in detail, other than describing how it can be employed as a strategy while restoring normal services (see Table 3 below). In the same Figure 1 example, water quality serviceability is provided to only about 25% of the customers immediately after the earthquake. The quality serviceability cannot exceed the water delivery serviceability. Since the system is delivering water to 60% of the customers, then 35% of the customers are receiving water not meeting the quality they received prior to the earthquake. Quality serviceability below 100% means at least some of the water delivered cannot be certified as meeting minimum health standards except possibly where systems maintain higher standards; for this paper, quality services are described in terms of public health standards. Following an earthquake, the potential for contaminants to infiltrate into the water network is high, as a result of water pipe breaks, low water pressure, sewer pipe breaks, contaminant spills and releases, and other factors. The lower quality serviceability is due to the ability of these potential contaminants to flow into other parts of the network combined with potential damage to water treatment components. Following an actual earthquake, some customers who are issued a water purification notice due to concerns with poor water quality may actually be receiving water meeting health standards. The reason for this discrepancy is due to the nature of widespread water leaks and variation of flow through the network making it difficult to define exactly where the health standards may be breached due to infiltration of contaminants; normally, assessments relating to health and safety are

8 1494 C. A. DAVIS conservatively estimated. The quality service levels off and begins to increase as the system is contained, as similarly described for the water delivery services; disinfectants are applied to the water; and tests are performed. The ability to fully restore water quality service is dependent upon the ability to operate such critical facilities as treatment plants and chlorination stations, deploy temporary treatment and disinfection stations, and repair/isolate pipe network damage. In cases where external factors change the water quality, full restoration may also require changes to treatment processes and possibly additional treatment facilities. The fire protection serviceability in Figure 1 is shown to immediately drop to zero. This indicates no fire service connection has the capability of meeting the pressure and flow demands required for normal fire protection service (e.g., CBSC 2007). Fire protection serviceability increases as portions of the system are restored to meet the fire-fighting needs. Under the definitions provided in Table 2, it is possible to protect 100% of the service area against the fire hazard without the entire network having the capability to meet the fire flow demands. This is because the fire-fighting equipment can hook up to another fire service connection and relay the water to any place in the service area needed for firefighting purposes. A distinction is made here between the ability to provide fire protection service through the pipe network and the ability of firefighters to protect an area using their equipment along with water supplied through the pipe network. If special fire protection service subsystems are developed, either separate or within the same network providing all other services, it is possible to achieve complete fire protection service restoration in advance of water delivery to all other service connections (i.e., the fire subsystems could reach 100% restoration in advance of delivering water to all other customers). Strategies useful for achieving this are presented later in this paper. Immediately after the earthquake, the quantity serviceability in Figure 1 drops to about 20%. This is significantly lower than the water delivery service and results from the inability of the network to provide flow at pre-earthquake rates and pressures, which is usually a result of damage to supply lines, the distribution network piping, pumping stations, and the reservoirs and regulating stations controlling the water flow. The quantity serviceability is increased as these facilities are repaired and returned to operation. A critical factor in restoring the quantity service back to 100% is the ability to provide an adequate water supply. The inability to return adequate supply sources or utilize alternate sources requires water conservation and rationing. As a result, severe impacts to supply sources could result in reduced quantity services for long durations, such as those shown on the horizontal portion of the curve in Figure 1. In some cases, it may be possible for the quantity services to be restored without meeting the pre-earthquake pressures, if water volumes can meet pre-earthquake normal customer needs. As an example, a damaged reservoir takes much longer to repair than the transmission and distribution pipes and residential customers at the far end of the line receive water flow sufficient to fulfill their daily needs without the reservoir, but at a reduced pressure; the flow reliability is reduced and may be periodically interrupted. However, in most cases, the pressure requirements are generally met along with or prior to the quantity services. Figure 1 shows a bounding curve identifying the times and percentage of customers for which services are considered fully operable (i.e., able to provide water delivery, quantity,

9 WATER SYSTEM SERVICE CATEGORIES, POST-EARTHQUAKE INTERACTION, AND RESTORATION STRATEGIES 1495 quality, and fire protection services) to customers. Operability for this example is dictated by fire protection and quantity service restorations. The functionality service drops to about 20% in the Figure 1 example. At some time after the event, operability increases more rapidly than the functionality. This mainly results from the ability to isolate damaged network areas and utilize existing or create temporary flow path redundancies and alternate supply sources. The network may return 100% operability to customers, but not necessarily with the same pre-earthquake performance or reliability. Normally a water system maintains a certain excess capacity to provide a safe and reliable product. This is accomplished by maintaining sufficient materials, supplies, crews, excess storage, system redundancies, and so on. An earthquake can easily stress the system well beyond its reserve capacities. For example, many parts of a distribution network may have redundant supply reservoirs and transmission mains serving water to the same pressure zone. Some of these facilities may be severely damaged and may take months or even years to repair. In the meantime water can still be supplied once the other, less-damaged facilities are repaired and returned to operation. However, the network operates with much less reliability, and if any part of the remaining network must be temporarily removed from service for maintenance or repairs as a result of the earthquake or otherwise, one or all of the other service categories may be disrupted to some or all customers. Aftershocks can cause decreases in functionality service and all the other service categories by increasing the system damage state. The recent earthquake sequence affecting Christchurch, New Zealand, exemplifies this problem (TCLEE 2015). Functionality characterizes the ability of a water system to operate in a damaged state and provide water in a manner customers are used to receiving (i.e., how a system can provide some or all of the other services in Table 2 and even full operability while in a damaged state). The functionality service cannot drop to zero unless the water delivery service cannot be met. As long as some water is capable of being delivered to some customers, the system maintains a functionality service level above zero. Figure 1 shows the fire protection service level, and thus an operability level, lower than the functionality service level for a short time after the earthquake. This occurs in the example because water delivery services did not drop to zero, but there is not adequate pressure and/or volume to meet fire service demand in the system immediately after the earthquake in any part of the system. Figure 1 also shows fire protection service and operability rapidly increasing above the functionality service level soon after the earthquake. The two functionality characteristics of (1) not becoming zero unless water delivery becomes zero, and (2) functionality bounding all other services at complete restoration requires any service dropping below functionality to cross over, or overlie, the functionality restoration curve prior to returning to normal service levels (i.e., 100% on vertical axis). As repairs are made and components return to operation, the functionality service increases. An earthquake exposes system vulnerabilities, and as a result, many times the restorations account for the newly recognized, or previously disregarded, vulnerabilities by mitigating them during the repair stage or in the following years. This can have a net effect of increasing the operational and functional performance and reliability above what existed before the earthquake. As seen in Figure 1, the functionality service reaches 115%, exceeding the pre-earthquake functionality. The functionality restoration is highly dependent upon available funds and other resources, because projects needed to restore

10 1496 C. A. DAVIS functionality are usually very costly; the more limited the funds and resources, the longer the functionality restoration. Insufficient funding or resources may result in the long-term functionality service being less than the pre-earthquake level (i.e., <100%). The service restoration curves in Figure 1 and the related descriptions are intended to be general and cover all types of water systems (although not all systems provide all services represented in Figure 1), and for distribution networks all customers within a service area. Water distribution networks are normally divided into distribution areas and/or pressure zones. A similar set of restoration curves can be developed to represent each distribution area or pressure zone. Each area or zone has a different set of curves. Those suffering greater damage or loss of supply usually have lower serviceability and longer restoration times. Some zones, or portions of zones, may have complete loss of services while others have none. The Figure 1 curves intend to represent an average throughout an entire system. Figure 1 only accounts for the time to restore the water system. The restoration of water distribution within buildings and business or industrial complexes requires plumbing repairs to the internal piping network after the primary service is restored and before service to each resident, commercial, industrial, or other customers can be restored. For most locations, excepting buildings and complexes sustaining severe damage, the final water service obtained by customers within their homes and businesses is expected to be equal to the primary water system or lag slightly behind by a few days to account for local plumbing repairs. Figure 1 assumes the normal pre-earthquake service level (i.e., the horizontal line at 100%) remains stable during and following the earthquake event. The previous descriptions only indicated the functionality services may have a final restoration not matching the preevent level. However, it is possible for all service categories to have a short-term or long-term stability not matching the pre-event service levels (Holling 1996, McDaniels et al. 2008, Cimellaro et al. 2010). This involves a service equilibrium shift (SES) in the net loss or gain in serviceability (a gain is shown for functionality in Figure 1). In many cases, any potential SES is a function of the water system s interaction with the greater community s resilience. A net loss in services may result either from the inability of a damaged water system to support the pre-event number of services or the inability of the community as a whole to sustain the number of people and industries, regardless of the water system s ability to support the services. The 11 March 2011 Great East Japan earthquake and tsunami disaster in the Tohoku region of Japan provides numerous examples of this problem (e.g., Suppasri et al. 2012). The destroyed communities were not sustainable to the tsunami hazard, resulting in a permanent decrease in the total number of water service connections. At some point after an event causing a permanent SES, the curves need to be re-normalized by the post-event service capabilities to account for the permanent change. More research is needed to better understand the interaction of water system and community post-earthquake sustainability. Figure 2 shows an example quantity restoration curve having a temporary 40% reduction and a permanent 20% reduction. This may result from an earthquake severely impacting water supply sources, such as ground water wells, aqueducts, or other sources. In this example, a 40% or greater conservation is needed between times t 0 and t 1. At time t 1, an additional 20% of water supply is restored, but the community must now adjust to a permanent 20% loss in water supplies. Restoration curves similar to Figure 2 may be created for any of the service

11 WATER SYSTEM SERVICE CATEGORIES, POST-EARTHQUAKE INTERACTION, AND RESTORATION STRATEGIES 1497 Figure 2. Example quantity service equilibrium shift (SES). Refer to Table 2 for quantity service definition. categories presented in Table 2 and may even show an increase in services as indicated for functionality in Figure 1. The SES characteristic shown in Figure 2 as a permanent loss is not inherent to all water systems, but may result from certain extreme events. The example in Figure 1 shows all categories having a common trend of initial service declination then an increase in service restorations until completed. In real post-earthquake situations, the ability to maintain a continuous upward trend, once initiated, is highly dependent upon how the restoration activities are managed. After controls are established to stop the downward trend, managers in charge of restoration should make decisions to target a continued upward trend in restoration. It is possible to have a drop in services within the upward trend; a case in which this has occurred is presented in the next section. Repeated serviceability drops (even just one) can have significant ripple effects and potentially serious impacts to the community. CASE STUDY OF LOS ANGELES WATER SYSTEM RESTORATION To further illustrate service restorations, results of an actual water system earthquake performance and post-event service restorations are presented for Los Angeles following the 1994 Northridge earthquake. This case identifies the importance for documenting post-earthquake restorations for all water service categories. Case studies quantifying water system performance capabilities improve our currently limited knowledge on the

12 1498 C. A. DAVIS complex interactions between (a) the service categories and (b) water service restoration and community resilience. On 17 January 1994, a moment magnitude (M w ) 6.7 earthquake struck the northern area of Los Angeles and caused significant damages to the Los Angeles Department of Water and Power (LADWP) infrastructure. In summary, there were 14 repairs made to the raw water supply conduits, more than 60 repairs to treated water transmission pipes, 1,013 repairs to distribution pipe, over 200 service connection repairs, 7 reservoirs were damaged, half the treatment plant was temporarily removed from service, and some other incidental damages. Total water system repair costs reached $41 million. Davis et al. (2012) describes the damage, water outage areas, post-earthquake system performance, and service restorations, which are summarized here. Figure 3 shows the water service restoration curves for the LADWP following the 1994 Northridge earthquake calculated as the ratio of customers receiving the service after the earthquake to those with the service before the earthquake. As seen in Figure 3, the water delivery service dropped to about 78% shortly after the earthquake due to water leaking from broken pipes. The LADWP s ability to contain the impacted area and initiate restorations rapidly allowed the water delivery services to increase soon after the earthquake. The quantity and fire protection services dropped to a low of about 72% on 17 January The quality service dropped immediately to zero because a water purification notice was issued 100 Normal Service Level Quantity L os Angeles Water Service (%) _ Northridge Earthquake Water Delivery Fire Protection Operability Quality Functionality 0-1 t Time (days) Figure 3. Los Angeles water system service restorations following the 1994 Northridge earthquake. Operability is not a service; it is a milestone delineating collective restoration of water delivery, quality, quantity, and fire protection services.

13 WATER SYSTEM SERVICE CATEGORIES, POST-EARTHQUAKE INTERACTION, AND RESTORATION STRATEGIES 1499 across the entire city within three hours after the earthquake. As shown in Figure 3, the water delivery service was restored to 100% at about 7 days, quantity and fire services at about 8.5 to 9 days, and quality service at 12 days after the earthquake. The rapid increase in quality service within one day after the earthquake resulted from recognizing much of the system was not damaged and water quality was maintained. Around two days after the earthquake, the drop in quality service for about three days resulted from the realization a portion of the pipe network where the water purification notice had previously been removed suffered greater damage than initially recognized; upon recognition, the notice was reinstated. The remainder of quality restoration was primarily due to disinfecting the broken pipe network after sufficient repairs were completed to restore flows and pressures. Figure 3 shows the operability state was completely governed by water quality restorations. The Los Angeles water system has a high level of supply and transmission redundancy which was utilized to provide continued services through the undamaged portions of the system. The functionality service restoration is calculated using the methodology described by Davis (2014a) for the supply, treatment, transmission, and distribution subsystems. The functionality services initially dropped to about 34% and began to improve soon thereafter as restorations were undertaken to the supply and transmission subsystems. As seen in Figure 3, functionality service does not initially track with operability or any of the other service categories; this is because damage to the supply reduced reliability to a much greater area than the main damage zone. The functionality service rapidly increased to about 60% once critical repairs to major supply and transmission lines were completed a few days after the earthquake, followed by a relatively linear increase to 70% for about the next two weeks. At 30 days after the earthquake, functionality services reached 82%, after which there were long periods between repairs, making relatively small incremental restorations until the functionality service returned to normal at about nine years after the earthquake. Several improvements were made to the system as a direct result of knowledge gained and repairs made following the 1994 earthquake; these were initiated at about six years and increased reliability above the pre-earthquake levels after about nine years. All improvements were completed after 18 years resulting in a positive SES, thereby increasing the post-earthquake functionality to 105% and increasing future seismic performance capabilities. The water delivery, quantity, fire protection, quality, and functionality curves are calculated from recorded data and show that the service categories in Table 2 can be applied to characterize postearthquake system performance. INTER-RELATION BETWEEN SERVICE CATEGORIES Table 2 and associated descriptions herein identify a basic hierarchy in restoring water services. First, water is delivered and then the fire protection, quality, and/or quantity are improved, followed by restoring system functionality. For systems sufficiently resilient to the earthquake hazard, some or all of the services may be restored at the same time, as described for the Los Angeles system in Figure 3 (quantity and fire protection). The portions of a system suffering significant damage may exhibit interactive characteristics between different service categories. The following describes some important interactions and competing issues between different water service categories; formulations for quantifying the interactions are left for future work.

14 1500 C. A. DAVIS WATER DELIVERY QUALITY INTERACTIONS When water delivery is linked to quality service restoration, the inability of the water system to properly treat the water results in the delay of water delivery, which in turn delays the restoration of all service categories. As a result, if the water quality subsystems are sufficiently damaged to cause any significant delay in delivering water to customers, then the delays result in compounding effects for other water services. For distribution networks that provide all the service categories shown in Table 2, which is very common in most modern urban water systems, damage to water quality treatment systems may have severe impacts on the ability to deliver water for any purpose in portions or all of the distribution subsystem. Figure 4 presents restoration curves for an example case where all treatment capabilities are removed to 75% of services and there is no bypass to the treatment plants; treatment plant damage removed all capability to deliver water to 75% of the services. Figure 4 is a revision to the Figure 1 example restorations and shows the water delivery restoration time roughly equals to the sum of the water delivery plus water quality restorations of Figure 1. For this simplified example, water flow in the pipes is required to identify where repairs are needed, followed by testing within the repaired network to ensure compliance with water quality standards. As shown in Figure 4, even the quality restoration is delayed further than shown in Figure 1 when the water delivery service is linked to the quality service. The other service category restorations are also delayed relative to Figure Normal Service Level Water Service (%) Earthquake Event Figure 1 Water Delivery Figure 1 Quality Water Delivery and Quality Quantity Functionality 20 Fire Protection 0-1 t Time (weeks) Figure 4. Example service restoration curves where water delivery is linked to quality services. Service restorations are delayed compared to those in Figure 1.

15 WATER SYSTEM SERVICE CATEGORIES, POST-EARTHQUAKE INTERACTION, AND RESTORATION STRATEGIES 1501 In cases where treatment facility damage does not prohibit water flow, but where water quality cannot be assured, water system managers and regulators may be confronted with conflicting priorities between the need to deliver water through the pipe network and the inability to meet health regulations. Some locations do allow non-potable water deliveries as long as risk management strategies are applied by informing the public health officials and customers that the water is not purified and advising them on how to purify the water for potable use (e.g., CDPH 2003). In some regions, the water quality regulations may not address the need for communications related to potential risks associated with water delivered for domestic use prior to ensuring it meets the public health potable water guidelines (e.g., Japan Ministry of Health Labor and Welfare 2010, Japan Water Research Center 2012, Hirayama 2011). When making the determination to deliver non-potable water, the differences in water service restorations as explained for Figure 4 relative to Figure 1 among other things, including risk communication, should be considered. Davis (2011) explains some related and practical issues delaying post-earthquake pipe repairs when water delivery services are delayed. QUALITY FIRE PROTECTION INTERACTIONS When fire protection services are provided through the same pipe networks providing the quality services then the local water quality policies or regulations may cause conflict between accomplishing the quality and fire protection objectives, similar as described for the water delivery quality interactions. Significant detriments to firefighting capabilities can result in those areas where water cannot be placed in the system in advance of meeting water quality standards; water delivery is a prerequisite to providing fire protection service. QUALITY QUANTITY INTERACTIONS Similar to the description for quality fire protection service interactions, delays in providing water delivery due to water quality concerns within the distribution network may result in further delays in restoring quantity serviceability. Additionally, earthquakes may affect supply source quality and effectively deplete available supply volumes. These interactions may go beyond or not even involve public health regulations, depending on water use and quality impacts. WATER DELIVERY QUANTITY INTERACTIONS The water delivery restorations are dependent upon the total quantity of water available to deliver to customers. Without restoration of water supply volumes, the delivery to all customers may be limited, and/or water rationing may need to increase to ensure that the available water can be delivered to all customers. Davis and O Rourke (2010) described a situation in Los Angeles where water may be delivered to all customers, but severe water rationing may be necessary for many months due to lack of water supply subsystem restorations following an M w 7.8 earthquake on the southern San Andreas Fault. FIRE PROTECTION QUANTITY INTERACTIONS The fire protection and quantity services have similar operational objectives, and as a result, when both services are provided through the same network, as one restoration is

16 1502 C. A. DAVIS being achieved, it usually aids in achieving the other service restoration. When quantities are limited, firefighting may be inhibited; quantity services may be lost in some areas to help maintain fire services. FIRE PROTECTION WATER DELIVERY INTERACTIONS Water system damage affects the ability to deliver water. The inability to isolate system damages and protect valuable supplies impacts fire protection services. Attempts to fight fires using water from systems struggling to operate may result in a complete loss in water delivery services in some areas. This is related to the strategy for network isolation to enhance water delivery and fire protection services in the following section. FUNCTIONALITY OPERABILITY (ALL OTHER SERVICES) INTERACTIONS As indicated in Figures 1, 3, and 4 it is possible for all other services to be met and the system be operable without having a high functionality service. Functionality service less than 100% simply means the other services may be provided but they are more vulnerable to impairment or outage under normal operating conditions, or from an aftershock, than prior to the earthquake. Systems having low redundancy and isolation capabilities may not be able to restore services without significant improvement to the functional serviceability. Resourceful systems having high redundancy and isolation capabilities may be able to improve operability with little change in functionality. This is a characteristic of the system represented in Figure 1 where the services making up operability (collective restoration of water delivery, quality, quantity, and fire protection) are effectively decoupled from functionality and improve rapidly while functionality only increases in steps when infrastructure repairs are completed. SERVICE RESTORATION STRATEGIES The service restoration features can be used as engineering principles to improve overall system performance. Some strategies that may be implemented separately or in combination to improve water system seismic performances are summarized in Table 3 in relation to the service restoration features already described. Davis (2011) describes several service restoration strategies in more detail. The strategies in Table 3 may increase serviceability and decrease the total time needed to complete restoration, but in and unto themselves may not completely restore any service category. The strategies can be implemented across entire networks, for certain zones within a network, or to improve water services to any specific critical lifeline or emergency service within the community. The strategies described are only intended to give examples in the context of the service categories described herein and are not intended to be a comprehensive listing; there are many additional strategies which can be utilized to improve seismic performance of water systems (e.g., Ballantyne and Crouse 1997, Davis 2008, among others). The service restoration strategies are complementary to other strategies intended to reduce seismically induced damages to water system components, which are not described herein.