How a Florida community documented stormwater assets in one year using in-house staff.

By Shawn M. Landry and Naomi M. Oliver

Hillsborough County, FL, like so many other communities throughout the United States, faced the need to efficiently manage its stormwater infrastructure to comply with government regulations, respond to citizens' needs and flooding concerns, and ensure the long-term functionality of its stormwater drainage system assets. With the assistance of the Florida Center for Community Design and Research, a service-oriented University of South Florida research center, Hillsborough County completed a rapid inventory of all stormwater pipes and structures to comply with government regulations. This article highlights the cooperative effort undertaken by the county and the university that resulted in the global positioning system (GPS)—based inventory of nearly 250 mi.² in one year, the consolidation of more than 800 lin. mi. of pipe and more than 100,000 stormwater structures into an ArcInfo GIS (geographic information system) database, and the development of an asset management system to assist staff in meeting regulatory requirements.

Municipalities across the US have been developing comprehensive and consolidated GIS-based infrastructure inventory databases for many years. These inventory efforts have included such techniques as digitization of paper-based inventory maps, field sampling using traditional survey methods, and various GPS-based efforts. Despite a wide variety of approaches to conducting infrastructure inventories, historically the primary impetus behind conducting a stormwater infrastructure inventory has been compliance with federal National Pollutant Discharge Elimination System (NPDES) regulations. Recently, two additional government programs have forced communities to further evaluate their stormwater infrastructure: Governmental Accounting Standards Board (GASB) Statement No. 34, and the Federal Emergency Management Agency (FEMA) National Flood Insurance Program (NFIP) Community Rating System (CRS) Credits for Stormwater Management and Drainage System Maintenance.

Although many people involved with stormwater work are intimately familiar with the requirements of NPDES permits, a few of the requirements that are of particular interest for Hillsborough County include:

• developing an inspection program to enforce ordinances prohibiting illicit connections and illegal dumping into the stormwater system,
• performing inspections and maintenance of stormwater structures and roadside ditches,
• maintaining an internal record-keeping system to track inspections and maintenance activities,
• conducting an annual assessment of the effectiveness of inspection and maintenance schedules.

It is clear that meeting these requirements of the NPDES permit is nearly impossible without a stormwater infrastructure inventory. According to Phil Coram, administrator of the NPDES Stormwater Section at the Florida Department of Environmental Protection, emphasis on compliance with NPDES permit requirements will increase as Phase II of the program is implemented and EPA turns over administration of the program to the state level. Most professionals agree that compliance (especially demonstrating compliance) will be much easier for communities that maintain an infrastructure inventory.

NFIP makes federally backed flood insurance available in communities that agree to adopt floodplain management ordinances. In hurricane- and flood-prone communities, such as those of coastal Florida, NFIP is critical to insuring and protecting property. According to the Hillsborough County Web site (www.hillsboroughcounty.org), property valued at $2.8 billion is currently covered by NFIP in Hillsborough County alone. Reducing premiums paid to NFIP is important to citizens and thus is emphasized by elected officials. CRS credits provide a mechanism for communities to reduce flood insurance premiums by implementing measures aimed at reducing flood damage to existing developments or preventing damage to new developments. According to Eugene Henry, hazard mitigation manager for Hillsborough County, consulting firms throughout Florida have increased their emphasis on selling stormwater-related projects based on the potential to obtain CRS credits. Unfortunately, few firms or communities fully understand the complex nature of CRS credits to the degree necessary to realize these potential benefits to CRS programs as a result of stormwater projects. Despite this lack of understanding, most professionals know that to obtain any substantial credits, the community must be able to identify the location of the drainage system, conduct regular inspections and maintenance, and predict and repair inadequate components of the drainage system.

Finally, one additional reason behind infrastructure inventory efforts has emerged that affects the way government entities view infrastructure: GASB 34, Basic Financial Statements–and Management's Discussion and Analysis–for State and Local Governments. GASB 34 mandates that governments report all capital assets, including infrastructure assets, in their financial statements. (More information on GASB is available on-line at http://accounting.rutgers.edu/raw/gasb.) As related to network infrastructure (e.g., stormwater infrastructure), the mandate provides two options for a government to account for these assets, by either (1) reporting depreciation expense or (2) establishing an asset management system and demonstrating that assets are being maintained at a certain functional level. Many communities have determined that the second option is more appropriate because citizens already expect infrastructure to be managed at or above a functional level, and therefore an asset management system will serve the internal and external needs of the community. For managers of stormwater infrastructure without a consolidated inventory, GASB 34 poses an important question: How does a government demonstrate that assets are being managed if it cannot even demonstrate that it knows what assets exist?

Hillsborough County in west central Florida

How do these guidelines and regulations affect stormwater infrastructure management? Periodic inspection of part or all of the storm drainage system is required by NPDES and NFIP regulations to prioritize maintenance and by GASB to document system condition. Maintenance of the drainage system is required by all three regulations to ensure functionality of the entire system, while increasing (or targeting) maintenance efforts may result in additional CRS credits. Finally, modeling of the drainage system to predict flood-prone areas or prioritize water-quality problems is an important tool to meet NPDES requirements or to increase CRS credits, especially when used as part of a comprehensive stormwater management program.

To meet these inspection and maintenance needs, the most basic requirement of an infrastructure inventory is the documentation of the type of structures (i.e., assets) that exist and the location of these assets. At a minimum, the inventory must include enough information to allow inspection and maintenance teams to locate individual structures, record inspection results, prioritize maintenance needs, and issue maintenance work orders.

Modeling efforts require substantially more information because the typical stormwater model involves modeling the hydrology within a large land area. For modeling efforts to be conducted, stormwater assets must be connected within the larger network of a stormwater drainage system so that the hydrology of a given land area can be determined. In addition, detailed information often requires accurate elevation data, physical size of conveyance structures, and material types in order to determine hydrology conditions. Many communities initially focus modeling efforts to include only major conveyance systems (e.g., pipes greater than 36 in. in diameter).

Hillsborough County's inventory effort focuses on meeting inspection and maintenance requirements. An unusual aspect of this effort, compared with inventory efforts in many other communities, is the approach taken by the county to partner with the University of South Florida and develop a rapid GPS-based inventory protocol that can be conducted by existing county staff. Methods used to conduct this effort, results achieved to date, planned improvements, and data collection and management techniques are described below.

Background

Hillsborough County is located in west central Florida at approximately 28° north latitude. The Hillsborough County land area is under the separate jurisdictional control of the City of Tampa, City of Plant City, City of Temple Terrace, and unincorporated Hillsborough County. Each of the four jurisdictional areas is responsible for the maintenance of stormwater infrastructure within its boundaries. The inventory effort described here was conducted within unincorporated Hillsborough County. Of the 1,048 mi.² of land area within Hillsborough County, 931 mi.² are under the jurisdictional control of unincorporated Hillsborough County. According to the Census 2000 Redistricting Data, the population of the entire county in 2000 was 998,948. Between 1990 and 2000, the population of the county increased by 20%, with the majority of this increase occurring within the jurisdictional area of unincorporated Hillsborough County.

Historically, roads and other infrastructure built during development activities became the property and responsibility of the county soon after completion of the new development. Developers were required to submit "as-built" plan documents that detailed the location and type of each asset, including the location of the stormwater drainage system. For many years, these as-built documents provided the only available information related to the location of county-maintained stormwater infrastructure.

Beginning in 1994, Hillsborough County embarked on a field sampling effort to develop a stormwater infrastructure inventory of county-maintained stormwater assets (pipes, inlets, manholes, and so on). Natural drainage features, such as creeks, ditches, and streams, were not included as part of this effort unless a regular maintenance program, such as mowing, reached these assets. This initial inventory effort involved locating stormwater structure positions relative to roadways, transferring positions to 1:200-scale rectified aerial photographs, and then digitizing data into GIS. This early inventory process often involved three or four separate teams of people and usually required several months, from start to finish, to complete the inventory of a single development. By 1999, five years later, Hillsborough County had inventoried approximately 75% of the total land area of 931 mi.²

In 1999, faced with approaching deadlines to remain compliant with NPDES permit requirements, the county realized that it would need assistance to complete the countywide inventory within a reasonable time period. Two ideas were proposed: (1) outsource the effort to obtain a point-in-time infrastructure inventory and (2) use existing county staff to conduct the inventory but obtain assistance to develop a GPS-based protocol. Faced with the need to continually update the infrastructure inventory in the rapidly growing community, the county chose to use existing staff rather than commit to a permanent dependence on an outside firm for ongoing inventory efforts. To assist this effort, the county entered into an interlocal agreement with the Florida Center for Community Design and Research, a nearby service-oriented research center at the University of South Florida (USF).

Research staff at USF had extensive experience in rapid field sampling within urban areas using GPS and other technology-based tools. The need to rapidly conduct the inventory of maintained assets was of primary importance. USF assisted the county in several ways, including:

1. development of a rapid GPS-based infrastructure inventory protocol,
2. provision of equipment and staffing to rapidly complete a point-in-time inventory of approximately 250 mi.² within one year,
3. conversion of inventory data into a comprehensive ArcInfo GIS dataset to replicate into the Hansen Asset Management system,
4. programming of a customized ArcView GIS application interface for non-GIS users,
5. training for county staff to conduct all aspects of inventory efforts, including GPS operation and GIS data processing.

In addition to the inventory effort targeted at mapping maintained assets, the county has been involved in a process of developing stormwater (watershed) management plans for each of the watersheds under jurisdictional control of Hillsborough County. As one component of these plans, primary stormwater conveyance systems (greater than 36 in. in diameter) were mapped with a level of detail required for hydrologic modeling efforts. Unlike the countywide inventory, mapping efforts related to these plans included both natural and constructed systems. After completion of all 17 of these plans, the county would have vertical position data for many of these primary systems and could integrate these data into its stormwater inventory.

Data Collection and Processing

Field Data Collection

Stormwater asset positional accuracy is a critical consideration when planning an inventory. Because horizontal accuracy is primarily important only to locate assets, a horizontal accuracy of 3.3 ft. is considered more than adequate. However, because vertical-control information is useful only if the accuracy is sufficient to determine water flow, vertical accuracy on the order of less than 1 in. is required in the extremely flat terrain of Florida. In recent years, affordable (less than $10,000), user-friendly, real-time differential GPS equipment has become available provides the capability to map a real-world position with a horizontal accuracy approaching 3.3 ft., often in less than 30 seconds. However, GPS equipment capable of achieving the vertical accuracy required in Florida is four to five times more expensive and often requires a much longer sample time. Because vertical positions of primary stormwater conveyance systems were being obtained as part of a separate watershed management planning effort, only horizontal position was required for this stormwater inventory. As a result, differential GPS units with a demonstrated horizontal accuracy (in Hillsborough County) approaching 3.3 ft. were chosen to record the location of each stormwater asset. The Trimble ProXR Differential GPS unit with the TSC1 data logger was chosen for this project.

In any data collection effort, a well-designed data dictionary is critical to ensure that accurate and comparable attribute information is recorded (Robbins, 1996; Dewberry and Davis, 2000). Because the data dictionary developed for the GPS-based protocol would have to be comparable to the data dictionary developed five years earlier, previously collected data elements were retained and a few additional attributes were added to increase the amount of information obtained during the GPS-based field inventory effort. Stormwater assets inventoried during this effort included inlets, outfalls, manholes and junction boxes, control structures, maintained stormwater ponds, and all pipes. Where possible, data constraints were added to individual parameters to ensure data integrity. A list of selected parameters is included in Table 1.

Table 1. Selected Attribute Parameters Collected During GPS Inventory

Although most of the attributes collected are typical for all stormwater inventory efforts, a few of the data elements deserve mention, such as digital photograph, inspection date, and condition. Although field staff were trained to identify the general type of stormwater structure (e.g., curb inlet), staff had not originally been trained to identify the engineering-level detail about specific asset subtypes. Rather than rely on field staff to identify these details, every structure was photographed so that office-based engineering staff could identify the specific subtype of structure, if necessary. Photographs also served to document the general condition of the structure and the condition of the surrounding roadway or drainage area. During the prior inventory efforts, field staff were required to rate the condition of each asset as "good," "fair," or "poor"–vague information at best. The GPS data dictionary was improved to include an inspection date and a more detailed description of asset condition (cavitations, obstructed flow, corroded, damaged ends, and so on). Although this asset condition information is sufficient to meet the basic needs of inspection for NPDES, FEMA, and GASB, future refinements should include more quantitative measures of functional performance.

During the field inventory effort, emphasis was placed on rapid data collection. Field teams systematically visited one section-township-range at a time, recording the location and attributes of assets using the GPS data logger. On the rare occasions when GPS positions could not be acquired (approximately 2.5% of all assets), field teams recorded all attributes using the data logger but recorded the location on a 1:200-scale aerial photograph for later digitizing. Although this technique resulted in a reduction in accuracy of stormwater asset locations, such a reduction was considered acceptable to ensure completion of the field inventory within one year. It is important to note that each asset in the final database was tagged to identify the relative accuracy of each asset.

In addition to recording stormwater assets, inventory teams were tasked with identifying the location of any suspected illicit connections or illegal dumping to the stormwater system to satisfy requirements of the NPDES permit. The inventory teams were well suited to this role, as they were already tasked with visiting every stormwater asset in the county. As these locations were identified, GPS data would be sent via e-mail to the appropriate county staff, whose task it would be to further investigate these locations.

Field staff from USF and the county formed three teams of two persons each. At the beginning of the one-year field inventory period, USF staff operated the GPS units and county staff identified stormwater asset attributes. After six months of field data collection, county staff took a Trimble-certified GPS class and then trained to operate the GPS unit in the field. By the end of the field inventory period, county staff were fully trained in the use of the GPS unit for the stormwater inventory and were able to continue the inventory (for new development) after USF staff were removed from the field team.

Data Processing

The final data formats for the stormwater infrastructure inventory data include ArcInfo GIS data and .jpg-format digital photographs. Field data collection efforts produced two types of data: GPS export files and digital photographs. To incorporate field GPS data into the consolidated ArcInfo GIS data, several critical data-processing and quality-control procedures have to be performed. Although the details of these procedures are beyond the scope of this article, it is important to mention that extensive experience with ArcInfo GIS processing techniques is necessary to complete this protocol. As was the case in Hillsborough County, it is unlikely that many county stormwater management departments have existing staff capable of performing data processing tasks. To solve this problem, USF geography students trained as ArcInfo operators processed all data during the first year of the project. During this time, Hillsborough County hired GIS staff with ArcInfo experience and USF provided further training to teach all steps of the data processing protocol. USF also created a data-processing manual to serve as a reference for county staff. County staff are now able to process inventory data without assistance.

GIS Interface to Asset Management System

Although a more suitable long-term solution might utilize a "thin-client" interface such as ESRI ArcIMS, an Internet-based mapping system accessible via a standard Web browser, the county chose ArcView GIS version 3.2 as an interim solution because it already owned enough ArcView licenses to serve all necessary users. The standard ArcView interface was programmed to provide a set of queries and other tools through the use of user-friendly buttons and menu selections. In addition, digital photographs (all 30,000 of them) are linked to the appropriate asset and can be viewed from within the interface. Users now locate individual stormwater assets (or systems) using this GIS interface and then use Hansen to issue work orders or record customer complaints related to the asset.

Inventory Status and Future Data-Collection Efforts

By January 2001, USF and Hillsborough County completed the inventory of maintained assets for all parts of the county except some of the newer developments completed after 1994. Using the GPS-based technique, 232 mi.² of land area was completed in one year, compared to 116 mi.²/yr. during the previous six years using the non-GPS method. As further evidence of the efficiency of the GPS-based protocol, Table 2 shows that more than 30,000 assets were recorded during one year compared with approximately 12,000 assets recorded per year during the previous six years. In addition to providing a more rapid inventory methodology, the GPS-based protocol resulted in improved horizontal-position accuracy. The results of a postinventory sampling using a randomized design indicate that GPS positions are accurate to 5 ft. and non-GPS positions are accurate only to 17.2 ft., a difference of 12.2 ft.

The final products of inventory efforts to date include an ArcInfo GIS coverage that incorporates all inventoried infrastructure, with topological relationships defined correctly for purposes of modeling. All attribute information, such as structure type and condition, are maintained in the same ArcInfo GIS dataset. These data are also replicated in the Storm Module of the Hansen Asset Management system. The Hansen Storm Module is used to track all work orders and customer calls (e.g., citizen complaints) within the county's Hansen system.

Table 2. Summary of Generalized Stormwater Asset Types Inventoried As of January 2001

As of mid-2001, the inventory data lack vertical-control information and complete connectivity with natural drainage systems (i.e., creeks, rivers, and ditches). As previously mentioned, vertical control and a complete drainage system inventory are necessary to conduct detailed hydrologic modeling. Using the vertical-control data collected during watershed management plan efforts, the county currently is working toward incorporating detailed primary drainage system information into the same ArcInfo GIS dataset where constructed assets are recorded. By maintaining all stormwater assets in one GIS dataset, Hillsborough County's Stormwater Management Section will be able to use the infrastructure inventory to meet the needs of inspection, maintenance, and modeling as required by NPDES, GASB 34, and FEMA.

Conclusions

Given time constraints resulting from NPDES permit-related deadlines, Hillsborough County chose to focus its efforts on rapidly completing a stormwater infrastructure inventory to be used for asset management. After seven years of work, the county finally has an infrastructure inventory useful for inspection and maintenance needs to fulfill the basic requirements of NPDES, GASB 34, and FEMA. For example, by using the ArcView GIS Interface with the Hansen Asset Management system to access these data, staff can more efficiently respond to a reported flooding event by identifying most drainage system problems while still sitting at their desks. Once a problem is identified, a work order to correct it can be issued, prioritized, and electronically tracked so that the status of the work is known at all times. Even more important is the ability to prioritize maintenance based on condition information or to schedule inspections and budget staffing requirements. Without the infrastructure inventory and corresponding asset management system, these primary tasks would require additional staff and resources, if possible at all.

Hillsborough County plans to direct future inventory efforts to include vertical-control information for primary conveyance systems and natural drainage systems. Once these data are combined into a single, topologically correct GIS dataset, the infrastructure inventory will serve the needs of hydrologic modeling and asset management. With proper GIS tools, staff will be able to identify the path of virtually every drop of water that lands within the county. Flood events will be easier to predict in real time, and water-quality problems will be easier to identify.

After several months of using the ArcView interface and Hansen Asset Management system within separate county offices, county staff found that the computer network infrastructure was not fast enough to support all users. As with most communities, Hillsborough County maintenance personnel are located in remote offices. Although most of these remote locations are connected via a relatively high-speed network infrastructure, the bandwidth required to access GIS data using the ArcView interface is not sufficient. To solve this problem, the county will experiment with Internet-based mapping using ESRI ArcIMS as a means of viewing GIS data from remote locations. The bandwidth requirement will be much lower because Internet-based mapping can use server-side processing to send compressed images of the GIS data to a standard Web browser. The county will provide access to stormwater infrastructure data, albeit with limited functionality, via an Internet-based watershed atlas (see www.wateratlas.org).

Finally, despite a recent trend to outsource many government services, Hillsborough County chose to make a commitment to conduct and maintain the stormwater infrastructure inventory using county staff. In smaller communities experiencing less rapid growth, employing full-time staff dedicated to an inventory effort might not be practical. With approximately 1,000 mi.² and a 20% population growth rate, however, Hillsborough County should benefit by having the in-house ability to maintain and expand the infrastructure inventory. The efficient GPS-based protocol highlighted in this article provides the tool necessary for this effort. It is important to remember that as long as development and maintenance activities continue, an infrastructure inventory is never complete, a fact that should not be overlooked during annual budget processes.

References

Dewberry and Davis Inc. Stormwater Infrastructure and Conveyance System Inventory Project Phase IIIA — Citywide Inventory. City of Greensboro Stormwater Services, Greensboro, NC. www.ci.greensboro.nc.us/stormwater/Documents/phase3a_report.pdf. 2000.

Robbins, Clarence H. "Stormwater Infrastructure Inventory Development." Public Works. July 1996. (Also available at www.woolpert.com/news/articles/ar0796.html.)

Shawn M. Landry is a senior scientist and Naomi M. Oliver is an assistant in research with the Florida Center for Community Design and Research at the University of South Florida in Tampa.

Home + About + Subscribe + News + Calendar + Glossary
Talk + Images + Advertise + Contact Us + Search + Register + Services

Erosion Control Magazine | MSW Management Magazine
Grading & Excavation Contractor | ForesterPress | Forester Media

© 2000 - 2002 FORESTER MEDIA, INC.