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14 C H A P T E R 3 Synopsis of Issues Two primary questions that arise both during the preparation of debris plans and in the imple- mentation of those plans are âHow much debris is there?â and âWhat is the mix of the debris?â The general categories of debris that might be expected from various types of disasters will be discussed in subsequent chapters, but this chapter will cover how to determine the amount of debris, for both pre-event forecasting and post-event estimating. During the development of debris plans, one of the key components that forms the basis of the plans is the anticipated amount of debris. Immediately after a disaster, an estimate of the amount of debris is extremely important in order to properly deploy resources and immediately begin the cleanup process. A timely estimate of magnitude of debris can provide the basis for: â¢ Updating the debris plans. â¢ Estimating impacts to existing waste management facilities. â¢ Developing estimates of various categories of debris: vegetative, white goods, household haz- ardous waste, etc. â¢ Determining whether the work can be accomplished with force account labor. â¢ Providing volume estimate information to contractors, when they are activated. â¢ Determining the need for temporary DMSs and the activities that will be required at those sites. â¢ Working with DOTs and DPWs to minimize traffic issues by developing specific hauling routes. Target Audience â¢ Emergency management planners. â¢ Debris managers. â¢ Solid waste managers. â¢ DOT/DPW managers. Debris Forecasting Models. Debris forecasting models are used in the planning phase to estimate the amount of debris that might be generated as the result of a potential debris-generating event. In recent years, models have been developed to forecast the amount of debris resulting from specific types of events. These models may also be used immediately before and/or after an event to obtain a first estimate of debris before onsite estimates can be made. The private sector also has devel- oped, and continues to refine, models that can be used with satellite/aerial photography, com- bined with ground checking, to project debris volumes closely following a disaster event. Debris Estimating
Debris Estimating 15 Historical Analysis. The most basic forecasting model is frequently called an historical analysis. It uses data from a previous local disaster or from a disaster experienced by a similar in size and demo- graphically common community. By using historical data and interviewing staff involved in the previous debris operation, information for forecasting debris volumes for similar future events can be obtained. That data would then be combined with information such as land-use changes, response capability improvements, changes in landfill capacity, changes in personnel and equipment, modi- fied laws and regulations, as well as other local factors. The resulting analysis should provide a first- cut projection of debris requirements to plan for a selected design event, for the targeted community. Community-Based Risk Analysis. This method employs land-use maps of the community as a basis for projecting debris. Areas of similar land use are carefully marked and measured. Samples of each land-use type (urban, industrial, etc.) are selected and projected debris volumes for each sample area are calculated. The results from each type of land use are then extrapolated to the total amount of the area that encompasses that particular land use. The results can be added together to obtain a projection for the entire community for the selected design event. This method has the advantage of providing a rapid means of projecting debris over portions of the community if a disaster does not impact the entire area. The impacted areas can be ana- lyzed separately or a debris projection of all impacted areas can be available rapidly. U.S. Army Corps of Engineers (USACE). In the 1990s, the USACE developed one of the first models to estimate the amount of debris resulting from hurricanes, using data from Hurricanes Frederick, Hugo, and Andrew. This model defined its design target as a Category 3 hurricane event affecting densely populated areas, and has been widely used for a variety of debris event projections. More recently, USACE has refined its hurricane debris model to reflect experience in estimating debris volumes and has adapted the model to use GIS technology. The storms that occurred in 2004, 2005, and 2008 provided significant experience in debris estimates. The use of ArcGIS (a software product of ESRI) allows rapid numerical calculations and scenario estimates. The calculations are simple; however, appropriate inputs require some knowledge/information about the probable impact area. The basic formula is: Q C H V B S( )( )( )( )= Where: Q = Volume of debris in cubic yards C = Storm intensity factor (increases with increased category of hurricane) H = Number of area households (determined by population/average size of household) V = Vegetation characteristic (considers vegetative cover) B = Commercial/business/industrial use multiplier S = Precipitation multiplier (a storm accompanied by or following heavy rains will have more uprooted trees) Because the more recent model includes greater flexibility in the storm intensity factor (C), the vegetation factor (V), and the storm precipitation factor (S), the factors for that model are included in the tables below. Factors used in the original model can be found in the U.S. Environ- mental Protection Agencyâs (EPAâs) Planning for Natural Disaster Debris, Document ID Number EPA530-K-08-001, issued in March 2008 (3). The C value is expressed in cubic yards (CY) and indicates the increase in debris per house- hold, including buildings, contents, and land foliage. The vegetative characteristics multiplier, V, focuses on the potential amount of disaster-related debris by taking into account various densities of vegetation, including shrubbery and trees, growing on public rights-of-way. The vegetation V factor is shown in the following table:
16 A Debris Management Handbook for State and Local DOTs and Departments of Public Works VALUES OF âVâ VEGETATIVE CHARACTERISTICS MULTIPLIER VEGETATIVE COVER Light Medium Heavy VALUE OF âVâ MULTIPLIER 1.1 1.3 1.5 Following the hurricanes of 2005, USACE reviewed the vegetation factor and found it under- predicted vegetation volumes that occurred in a number of more rural counties. It was apparent that basing vegetative debris significantly on population and households missed a key variable. After review of debris data and discussions with crews involved in debris removal, it was deter- mined that an additional factor of âmiles of public roadway as a factor of population densityâ was needed. While revisions have been made to the model based on these reviews, it has yet to be peer reviewed or published. The commercial/business/industrial multiplier, B, takes into account areas that are not single- family residential. It includes areas that are considered light retail, schools, apartments, shopping centers, manufacturing, and light industrial. This factor is summarized in the following table: COMMERCIAL DENSITY VALUE OF âBâ MULTIPLIER Light VALUES OF âBâ COMMERCIAL/BUSINESS/INDUSTRIAL USE MULTIPLIER 1.0 Medium 1.2 Heavy 1.3 The amount of rainfall that accompanies a hurricane varies from light to heavy, sometimes called âdryâ and âwet.â For storms of Category 3 or greater, this designation is very important. Wet storms saturate the soil, resulting in more uprooted trees and increasing the amount of debris that must be removed. Higher intensity storms typically cause more roof damage, expos- ing structure interiors to the elements and rainfall will also cause more interior contents to be damaged. The table for the S factor is as follows: VALUES OF âSâ STORM PRECIPITATION MULTIPLIER (Used in storms of Category 3 or greater) PRECIPITATION CHARACTERISTIC None to Light Medium to Heavy VALUE OF âSâ MULTIPLIER 1.0 1.3 Similar to the vegetation V factor, operational experience also found that modification of the rainfall factor, S, was appropriate with some approximation of expected rainfall (in inches of precipitation) included. The USACE continues to review and analyze data from tropical storms and hurricanes in an effort to improve the accuracy of the projective formula. Federal Emergency Management Agency (FEMA). Contractors for FEMA developed a com- puter model known as HAZUS that provides an estimate of debris resulting from earthquakes. It was originally developed for use on the West Coast of the United States. Subsequent HAZUS modules for flooding and wind events have been constructed. These models are generally used
Debris Estimating 17 to develop mitigation plans post-event but have been applied in several cases to events as they occurred. The HAZUS models develop debris values in tonnage and the model results include debris types that are grouped together; conversion to volume estimation can be challenging. Private Industry Models. Firms in the private sector have been looking into and developing predictive models ranging from the basic to the highly detailed. For example, there are GIS-based models capable of developing debris forecasts before an event, which can include specific post-event weather data to create even more accurate debris estimates following an event. These models can be used on a wide range of disasters, including hurricanes, tornadoes, floods, and even bomb blasts. Some versions of these predictive models have been developed for specific types of disasters, or for specific locations, and must be carefully reviewed to ensure applicability for a desired application. Debris Estimating Forecasting the amount of debris that could result from projected disasters provides valuable input for planning and initial response; however, it can be equally important to have a more accu- rate estimate following the disaster. Having more detailed knowledge about the mix, amount, and location of debris will assist the debris manager in developing priorities for removal, debris reduction and recycling, and establishing sites for temporary (or permanent) disposal. Addition- ally, the DOT or DPW can provide timely information on transportation routes that will require clearing to expedite debris removal. There are several methods and techniques that can be used to develop debris estimates, and the selection of which ones to use is based on time, experience of the estimator(s), required accuracy, schedule, etc. â¢ Ground measurements and calculations of a representative area can be done, and the results extrapolated over areas of similar land use. â¢ Aerial and satellite photographs of impacted areas taken before and after the disaster can be used. In some instances, post-disaster aerial photographs can only provide extensive informa- tion about the extent and magnitude of the area of debris. â¢ Predictive GIS models that are modified to include disaster-specific details (surge zones, inun- dation zones, high tide levels, wind band levels, microburst areas, etc.) can produce estimates of debris volumes and locations. â¢ Any of the remote-sensing approaches combined with systematic ground-based field crews for verification can produce more reliable data results. Equipment used by staff for ground mea- surements commonly includes measuring tapes, sketch pads, note paper, global positioning system (GPS) units, digital cameras, cell phones, and equipment needed for logistics and safety. Conversion Factors. Based on a large numbers of disasters and the amounts of resulting debris, several conversion factors and guidelines have been developed that assist in the calculation of a rea- sonable estimate of debris. Many of these can be found in FEMA Publication 329, Debris Estimating Field Guide (4). Conversion factors that may be of use are discussed in the following section: Building and Residences For many years, the formula for determining the amount of debris generated by a building was Length Width Height 0.33 27 CY Ã Ã Ã = (All building measurements are in feet) (The constant of 0.33 accounted for air space in the building.)
18 A Debris Management Handbook for State and Local DOTs and Departments of Public Works Following Hurricane Floyd in North Carolina, FEMA conducted an empirical study and developed a slightly different formula associated with a demolished single-family residence: Length Width S 0.20 VCM CY( )( )( )( )( ) = (Length and width must be in feet) S = Number of stories 0.20 = A constant derived from the study VCM = A vegetative cover multiplier The VCM is used to account for the vegetative debris associated with the house based on aerial photography, and is based on the following definitions. Light (1.1)âGround is more visible than trees, and canopy cover is sparse, usually new home developments. Medium (1.3)âHas uniform pattern of open space and tree canopy cover, most common description for vegetative cover. Heavy (1.5)âFound in mature neighborhoods and woodlots where ground or houses cannot be seen due to tree canopy cover. When applying the VCM to multi-story houses, the VCM should be applied only to the first- floor square footage. The following table (Table 3.1) shows the estimated debris from various sizes of single-family residences (from Debris Estimating Field Guide, FEMA 329) (4), using this estimation model. A good application of this tool would be to estimate the total debris from this tornado event, using a picture such as in Figure 3.1, combined with the sizes of houses, and information from Table 3.1. Information on the impacted development indicated the average house was 2400 square feet and a single-story structure. The number of destroyed homes was determined by viewing the aerial photograph and counting driveways. From these two numbers, the debris estimate of much of the impacted area was quickly calculated. There are additional conversion factors that have been developed by FEMA, the USACE, and debris specialists. These are in common use, and may make estimating faster and easier. Typical House (Square Feet) Vegeta ve Cover Mul plier None Light (1.1) Medium (1.3) Heavy (1.5) 1000 200 CY 220 CY 260 CY 300 CY 1200 240 CY 264 CY 312 CY 360 CY 1400 280 CY 308 CY 364 CY 420 CY 1600 320 CY 352 CY 416 CY 480 CY 1800 360 CY 396 CY 468 CY 540 CY 2000 400 CY 440 CY 520 CY 600 CY 2200 440 CY 484 CY 572 CY 660 CY 2400 480 CY 528 CY 624 CY 720 CY 2600 520 CY 572 CY 676 CY 780 CY Table 3.1. Estimated debris from destroyed single-family, single-story homes.
Debris Estimating 19 Conversion Factor: 1. Debris generated by a wide mobile home = 290 CY. 2. Debris generated by a double-wide mobile home = 415 CY. 3. Personal property brought to the curb from a flooded slab-on-grade home = 25â30 CY. 4. Personal property brought to the curb from a home with a basement = 45â50 CY. 5. Construction and demolition debris: 1 ton = 2 CY. 6. Mixed debris: 1 ton = 4 CY. 7. Vegetative debris: a. Hardwoods: 1 ton = 4 CY. b. Softwoods: 1 ton = 6 CY. c. 15 trees, 8 inches in diameter equals 40 CY (average). 8. One acre of debris 10 feet high = 16,117 CY. 9. Debris generated by a Category 3 to 4 hurricane generally will consist of: â¢ 70 percent clean woody debris. â¢ 30 percent mixed C&D. 10. Debris generated by a Category 4 to 5 hurricane will generally consist of: â¢ 30 percent clean woody debris. â¢ 70 percent mixed C&D. Of the 70 percent C&D: i. 42 percent will be burnable but will require sorting. ii. 38 percent will be landfilled iii. 15 percent will be metals. iv. 5 percent will be soil. (It should be noted that this is an estimate based on various hurricanes. The mix will vary depending on the location of the hurricane.) 11. Burning vegetative debris reduces the volume by about 95 percent. 12. Chipping and grinding vegetative debris reduces the volume by about 75 percent. 13. Debris may undergo volume changes during handling/hauling. 14. Leafy vegetation on the ground will have a reduction in volume when it is mechanically loaded into trucks. Figure 3.1. Damage to residential development by tornado. (Source: FEMA)
20 A Debris Management Handbook for State and Local DOTs and Departments of Public Works Figure 3.2 and the conversion factors for mobile homes were used to initially estimate disaster- related debris at this mobile home park. Example: In Figure 3.2 above, a review of the aerial photograph indicates that this mobile home park originally held about 160 mobile homes: 52 were totally damaged and 107 were left standing after the tornado. Of the remaining mobile homes, approximately 14% are double-wide assemblies. Applying that same percentage to the destroyed homes, a reasonable deduction is that 7 were double-wides and 45 were single-wide mobile homes. Single-wide Debris Estimate = 290 CY Ã 45 homes = 13,050 CY Double-wide Debris Estimate = 415 CY Ã 7 homes = 2,905 CY Total 15,955 CY It would also be reasonable to estimate that additional debris was created in some of the homes that were not totally destroyedâperhaps an additional 10â15% should be added to the tally. This results in a total estimated debris volume from this mobile home park of approximately 18,000 CY of mixed debris. These procedures and conversion factors provide information that can be used for 1) initial projections before a disaster occurs, and 2) estimates after the disaster. They also provide a means to help develop a workable plan, as well as accelerating the disaster recovery by better understanding the magnitude of the debris management requirement. Federal, state, and local governmental entities, as well as private firms, continue to develop and refine debris projection and estimating methods. Many of these may be appropriate for specific areas or events; however, they may not provide acceptable projections or estimates in other loca- tions. Before using such models, the software, input, calculating procedures, limitations, and output should be carefully reviewed. The output of any estimating model should not be used as a basis for payment. Figure 3.2. Damage to mobile home park 2005 Evansville area tornado. [Source: National Oceanic and Atmospheric Administration (NOAA)]