The Northridge earthquake of January 17th, 1994, caused extensive damage to the City of Los Angeles' sewer infrastructure. A Geographic Information System (GIS) played a crucial part in the City's effective response to prioritize, identify, and repair the sewer damages. The wastewater collection system network and various other GIS coverages were previously mapped or purchased as part of the City's Clean Water Program. A GIS system is routinely used for collection system planning, analysis, and evaluation. Immediately after the earthquake, information about the building damage, surface damage, and water pipeline rupture was collected from the agencies responsible for responding to this natural disaster. This data was then developed into ArcInfo coverages and overlaid on the existing coverages. Areas of the City were ranked and prioritized for closed-circuit television inspection and damage assessment based on the severity of the damage to the other infrastructure. GIS was used to analyze data, visualize the damage and expedite the inspection of sanitary sewer. Because the basic GIS was in place, an inspection and repair program was quickly and effectively developed. Then GIS was used to visually display the findings of the inspection and assist in concentrating the City's limited resources in the most urgent areas. GIS proved to be an important emergency response tool in the management of earthquake repairs.
On January 17, 1994, the Northridge earthquake, which measured 6.7 on the Richter scale and its aftershocks caused vast damage to the City of Los Angeles' infrastructure. This paper describes how ArcInfo played a major role in identifying, monitoring, and tracking earthquake- related sewer damage. Preceding the earthquake the City of Los Angeles' Bureau of Engineering developed a GIS system using ArcInfo for wastewater flow estimating and modeling. All of the sanitary sewers within the City had been digitized and all pertinent coverages such as sewer map grid, political and geographic boundaries for engineering analysis were available in ArcInfo.
The City's sewer network consists of about 7,100 miles of pipes within a 467 square-mile area. The sewers range from 8" to 150" in diameter. The sewers are made of various shapes and types of pipe materials: predominately circular clay with limited amounts of non reinforced concrete for the smaller pipe sizes and circular, semi-elliptical, and elliptical brick or reinforced concrete for the bigger pipe sizes. Figure 1 shows the locations of the epicenter and after shocks in reference to sewer lines within the City of Los Angeles.
Since sewer damage is not generally visible from surface, the City faced a challenge to identify and repair sewer damage to meet Federal Emergency Management Administration (FEMA) damage assistance deadlines. To ensure that dead lines are met, the project was carefully monitored through each tasks listed: Gather damage reports from other departments and agencies. Prioritize areas to perform damage assessment. Prioritize damage inspection. Display assessment progress. Evaluate the success of the methodology. Group the damaged sewers for repair project packages based on cost, size, landuse, topology, community impact, and contractibility. Monitor and track the progress of individual projects from assessment through repair. Create and update sewer maps showing the locations of the damage in reference to other related coverages.
Due to the large area, scattered damage, different types of damage, limited time and resources, and complexity of the sewer network, it was difficult to manage such a large project without the help of some kind of computerized process. Looking at many of the tasks listed above, GIS seemed an obvious choice for the needed quick and effective response. A flow chart of each step of the process, showing where GIS was used from the initial damage assessment through the repair of earthquake damaged sewers is attached.
After the earthquake, visual damage was documented and appropriate actions were taken by various departments of the City. All the collected information was made available to other groups.
The Department of Building and Safety inspected all the buildings within the City and evaluated damage that was found. Each building inspected was categorized by the severity of damage, and posted with red, yellow or green tags. This information was input into a database by the building's street address. Department of Land Development and Mapping created an ArcInfo coverage by address matching with Thomas Brothers' street base map, which is widely used in Southern California.
The Department of Water and Power identified and repaired water leaks throughout the City. This information was also referenced to a Thomas Brothers' street map. A database was created for identified water leaks with reference to Thomas Brother map and grid numbers.
The Bureau of Engineering did a windshield survey of surface damage to curbs, street pavements, and other visual damage within the City's rights of way. The listing of surface damage information was input into a database referenced by Thomas Brothers map and grid numbers.
Besides these earthquake-related damage assessment data, ArcInfo coverage for all sewers was available from ongoing planning studies. Sewers were categorized as major outfall, primary, or secondary sewers, where primary and major outfall are sewers equal to or greater then 18 inches in diameter, and secondary are sewers less then 18 inches in diameter. Major outfall and primary sewers were assigned unique identifiers which relate to outside databases. Also earthquake damaged secondary sewers were assigned unique identifiers to create a link with outside databases.
Other ArcInfo coverages such as earthquake faults, geology, liquefaction, shaking hazard, were developed from maps which were provided by County of Los Angeles. Coverage of epicenter and after shocks was developed from data provided by CALTECH. Street base map, geographic and political boundaries, and other reference coverages were already available in house.
Due to such a large area of the City and widespread and scattered damage, it would have been difficult to prioritize areas for inspection without the help of a GIS system. It was very important to quickly and effectively locate damaged sewers to meet FEMA and Operation Emergency Services (OES) deadlines.
Considering the magnitude of the work to be done and the available data, it was obvious that the ArcInfo would be a valuable tool to help prioritize the damage assessment. As stated earlier, building, water, and surface damage data were available in an electronic format. Using this database, each Thomas Brother map grid was given a separate score based on the type, severity, and number of reported damages. These calculated scores were then transferred from Thomas Brother map grid to Sewer map grid using overlay analysis. The combined score for each sewer map grid then was developed based on all three types of damage. The map grid was then prioritized based on combined calculated score. First three boxes on Figure 2 show a prioritized sewer map grid into four condition categories for building, street, and water damage. The final box of figure 2 shows a prioritized sewer map grid where the priorities are based on combined score of all three type of damages. Ultimately, these sewer map quadrant priorities were used to schedule the closed- circuit television sewer inspection with concentration in high-priority areas.
Sewer defects were entered into log sheets in the field as the sewers were televised. The information from these log sheets was then transferred to a database. Using the findings of the television inspection and previously developed ranking system for closed circuit television inspection, the sewers were field categorized by television inspection field crews from A (good condition pipelines) through E (pipelines needing emergency repair). These field made condition assessments were later verified and refinements were made. ArcInfo was used to display the results of the sewer condition assessment. Figure 3 shows the various conditions of the televised pipes. The design engineer decides what repairs, if any, should be made to the damaged sewers in categories B through E.
It was important to monitor inspection and damage assessment progress as it proceeded to maintain schedules and meet deadlines. Figure 3.1 is an example of status report of the television inspection using GIS. Sewer map quadrants are differentiated based on the amount of completion. This map provides a quick update and visual check of the television inspection progress. The findings of the sewer conditions correlated well with the original priorities.
City started filing its Damage Survey Reports (DSR) to FEMA while television inspection continued. Each DSR contained multiple sewer segments that were televised. The DSR were mainly used for funding purpose.
After a considerable amount of the sewers were televised and damages identified, the damaged sewers were grouped into reasonable sized project packages called units. Criteria for packaging considered; landuse, topology, size and cost of the project packages, community impact, construction barriers, DSR groups and other factors. Project packaging was done manually using GIS-generated maps. The GIS plots were created with sewers colored by DSR number, and displayed with landuse and other related coverages. These plots were used as working drawings to develop the project packages. Then, GIS was used to display the preliminary project packaging as shown in Figure 4. These maps were used to check the final packaging and evaluate the effectiveness of manual groupings based on the rest of the criteria. Based on the findings, refinements were made and projects were regrouped and replotted. This process was repeated until satisfactory results were achieved. The grouping of damaged sewers into repair projects was finalized before the design process.
Besides prioritizing work, displaying results, and grouping damaged sewers, GIS was found to be a very powerful tool for effectively tracking the progress of the projects. Each repair project goes through design, plan processing, bid and award, and finally construction. Figure 5 shows an example of how the project status is documented. The sewers are displayed with GIS graphics at various stages of process.
The earthquake damage assessment and repair received a high level of attention. In addition to FEMA staff, other engineering groups and upper management staff, and elected officials within and outside the City needed to be appraised of the status of the earthquake repair projects. The status needs to be continuously updated and presented on short notice. The GIS graphics is ideally suited for this purpose since they can be updated very quickly and can be readily tailored for presentation to various interest groups, because other reference coverages were already available. For example, in response to a request from a City council office, sewer damage within the given council district was displayed, and the amount, types of damage, and cost of the repair projects were presented. Many forms of presentation and report graphics have been prepared and many more are possible because of the flexibility and versatility of the GIS.
The Northridge earthquake and its aftershocks caused extensive damage to the City s sanitary sewer system. In a little over one year since the earthquake approximately 360 miles of sewers have been televised. Approximately 300 miles of the televised sewers were damaged by the earthquake. Nearly 100 projects have been identified for design and repair. Each project includes repair of several defective pipe segments. The City has started design of many of the project packages and will follow a fast track procedure for plan processing and bid and award. The GIS is being used to monitor the progress of each of these projects. Television inspection will continue for another approximately 6 months.
Sewer system defects generally could not be observed from the surface. The GIS helped to organized and prioritize the television inspection and condition assessment. The City was able to focus resources on the areas with the highest potential for severe damage as identified through the GIS analysis of other infrastructure defects. Damage, found by television inspection, was more extensive and more widespread than initially thought.
The sharing of data in a common readily importable format was valuable in setting priorities for the sanitary sewer television inspection. Information on building, street, bridge, and water pipeline drainage was available a few days after the earthquake. This information was used to prioritize the inspection of the sewer system. Data sharing was valuable and it should be a part of any municipal or regional emergency response plan.
The GIS helped to set a new standard for emergency response time. Up-to-date status reports were prepared on short notice and presentation graphics tailored to specific audiences by altering reference mapping were rapidly assembled. The versatility of the GIS was again demonstrated. The GIS was developed for sewer planning and various coverages were in place and current. Because of this, the GIS was immediately available for use as a tool for managing the damage assessment of the City s sanitary sewer system and tracking the subsequent repair work. This was an unanticipated benefit of the GIS.
In conclusion, because of the magnitude of this disaster, the extent of the damage, the difficulty in location the damage, and the necessity for careful tracking, the GIS was indispensable and clearly contributed to the effective management of the response to this disaster.
The authors wish to gratefully acknowledge the support and assistance provided by CSED team members; Ed Davanzo, Todd Mitchell, Elroy Johnson, Rafael Solorzano and Dale Cannon. Special thanks to the city departments who made data and information available for the success of this project.
DEVANG PARIKHRANDY PRICE
CIVIL ENGINEERING ASSOCIATE
CITY OF LOS ANGELES
650 SOUTH SPRING STREET, SUTIE 1000
LOS ANGELES, CA 90014-1918
PH: 213-847-8583
FAX: 213-847-8912