AWRA SYMPOSIUM ON GIS AND WATER RESOURCES
Sept 22-26, 1996
Ft. Lauderdale, FL
Abstract
Introduction
Trinity River Low Flow Conditions and Wastewater Treatment
Regional Urban Storm Water Management and USEPA Permits
Common Vision for Trinity River Corridor & Flood Damage Reduction
Conclusion
References
Authors
KEY TERMS: Water quality; urban storm water; flooding; GIS; Internet.
The Dallas/Fort Worth Metroplex is the nation's largest metropolitan area located on an inland waterway. Its population of 4.5 million is greater than 30 states. To assure an adequate long-term drinking water supply, each of the major branches in the upper watershed has been impounded with manmade reservoirs. Thus the Trinity River faces great extremes as it flows through the urban core, with low flows as small as 10 cfs to massive floods with the potential for billions of dollars in damages and loss of life (USCOE, 1995).
The North Central Texas Council of Governments (NCTCOG) is a voluntary association of more than 200 cities, counties and special districts in a 16-county region. NCTCOG is an association of, by, and for local governments. NCTCOG assists its members in planning for common needs, cooperating for mutual benefit, and recognizing regional opportunities for improving the quality of life in North Central Texas.
NCTCOG is the designated regional planning agency for comprehensive planning as well as functional programs such as water quality management. NCTCOG has actively addressed key water resources issues since developing an areawide water quality plan that was the first in the nation to be approved by the U.S. Environmental Protection Agency. Besides sustaining the areawide water quality planning process, NCTCOG coordinates one of the largest urban storm water programs in the country and serves as local sponsor for the U.S. Army Corps of Engineers' largest floodplain feasibility study, all directed at the Trinity River (USCOE, 1990).
Since 1989, a key tool in NCTCOG's planning program, particularly in the area of water resource management, has been the Regional Geographic Information System (GIS). The Regional GIS is a significant computing tool representing an intelligent mapping database that can link information to specific point or line features. NCTCOG has made heavy use of GIS to illustrate planning information for the region and explore management solutions. All of NCTCOG's functional departments, including the Department of Environmental Resources, use the ArcInfo GIS software through a network system. Arc/Info is run in a Unix environment using a Sparc Server 20 that has 288 megabytes of RAM and 30 GigaBytes of hard disk storage.
The agency set up an Internet site in May, 1995, and several departments have designed custom homepages featuring specific projects for their respective department programs. The Department of Environmental Resources homepage highlights a broad range of regional environmental initiatives, from water resource planning to air quality. Map products and coverage information have gradually been redesigned for access through the Internet homepage, with references to data and information developed at NCTCOG, as well as other Internet sites covering similar environmental topics.
The Trinity River is the major water feature that passes through the dense urban core of North Central Texas. The Trinity River presents many water quality and quantity challenges under three typical flow regimes: low flow conditions that require very stringent wastewater discharge limits; urban storm water runoff impacts during wet weather; and serious flooding from periodic storm events with potential damages in the billions of dollars (USCOE,1995). NCTCOG has major cooperative programs with local, state and federal partners to address each of these three critical situations, employing its Regional GIS as a fundamental tool for decision-making.
One of the first recorded impressions of the Trinity River is that of pioneer A. W. Moore in 1846 -- "The river a little narrow deep stinking affair" (Moore, 1846). Some would say it then got worse as the region was settled. In 1925 Dallas led the state in deaths due to typhoid, and the Trinity River was termed a "mythological river of death" in a State Health Department report (Texas Department of Health, 1925).
By the 1960's, the Trinity River was stressed during low flow conditions from poorly treated sewage and industrial discharges. The major cities and agencies were already turning serious attention to wastewater treatment improvements when NCTCOG developed the initial regional plan, the Upper Trinity River Basin Comprehensive Sewerage Plan (UTRBCSP), between 1968 to 1971. Many facilities were at or above capacity, with a significant number of aging community sewage plants discharging poor quality effluent (NCTCOG, 1971).
A keystone of the UTRBCSP was to phase out many of these smaller plants and divert wastewater flows to larger joint systems serving multiple customer cities. The region caught up with capacity needs by the early 1980's, with diversion of more than 95% of the wastewater flows to joint systems. The quality of wastewater discharge improved to a point where effluent quality is among the best in the nation (NCTCOG, 1985). From 1970 to 1994, the wastewater flows increased nearly 300% while organic loading, measured by Biochemical Oxygen Demand, decreased over 90%.
In 1996, NCTCOG prepared, and its Executive Board adopted, demographic forecasts for the region through the year 2020. A comprehensive review of current and future wastewater service needs from 1990 through 2020 was begun using the Regional GIS as the primary analytical tool. This effort, entitled the "2020 reVIEW of Wastewater Service Needs", used GIS to link planning basins, service area geographies, and demographic projections for the region (Figure 1). The results of this review are being incorporated into NCTCOG's 1996 Annual Water Quality Management Plan for North Central Texas. Working with area wastewater operators who participate on NCTCOG's Water Resources Council, NCTCOG identified current and future service area information. The assumption for North Central Texas, based on currently served areas, is that a population density of one person per acre or greater represents conditions that are highly likely to need organized wastewater treatment (NCTCOG, 1996).
Demographic projections for 6,000 small zones in the Dallas/Fort Worth metropolitan area were combined with per capita discharge rates for population and employment, inflow and infiltration factors, and other elements to project wastewater flows (Figure 2). The Regional GIS then routed these flows to designated facilities and compared them to anticipated treatment capacity. Accurate projections of wastewater flow for the region will also have future application with regard to a renewed state initiative to evaluate wasteloads for the upper Trinity River basin.
Figure 1
Figure 2
When it starts to rain, most people seek shelter. In North Central Texas, however, local government staff have been going out with U.S. Geological Survey staff to 30 automated storm water quality monitors across the region, gathering storm water samples and insuring that they are operating properly. The automated storm water monitors are part of one of the largest cooperative regional programs in the nation to understand and address urban runoff impacts (Promise, et al., 1993).
In 1990, the USEPA established the National Pollutant Discharge Elimination System (NPDES) storm water permitting program for separate storm drainage systems for selected industries and municipalities greater than 100,000 in population. NCTCOG coordinated the application process of the seven largest cities in the Dallas/Fort Worth metropolitan area which had to apply for Municipal Separate Storm Sewer System (MS4) permits. The application activities involved descriptions of the city storm drain systems, characterization of the storm water quality in those systems, and the quantity of storm water entering waters of the United States. Municipalities were also required to develop management programs utilizing Best Management Practices to improve the quality of the storm water to the maximum extent practicable. All of the information compiled during the application phases was to be used in designing five-year MS4 permits. All seven municipalities and two Texas Department of Transportation Districts coordinated efforts through NCTCOG to develop and compile information for submittal with the permit application.
The Regional GIS was a primary tool used to map storm drainage system information, outfalls, land use and other features called for in the application. A Regional Strategy for Urban Storm Water Management in North Central Texas incorporated plans for the ongoing use of the Regional GIS in maintaining maps of key storm water features and evaluating BMPs as part of the management program efforts (Promise, et al., 1993). While some of the participating municipalities had begun to develop their own GIS capabilities, the Regional GIS activities that were done through NCTCOG assisted in a more consistent, focused, and cost-efficient initiative.
NCTCOG regularly maintains and updates key coverages of land use information, monitoring sites, base map features, and other layers essential for evaluating storm water management programs. Working with a regional task force, NCTCOG assisted in designing a consensus program aimed at meeting the permit requirements and providing a regional perspective for storm water management. The Regional GIS was also used to meet individual needs of each city for the permit process, while at the same time portraying storm water information by its more appropriate storm system and watershed basis.
As an example, more than 5,000 individual major outfalls within the seven cities were mapped into the Regional GIS for the application process (Figure 3). Upon conversion to digital form, the outfalls can be linked to either their respective cities, a specific watershed, or other geographies as needed. An early initiative was the linking of storm drain screening data from dry weather periods to the outfalls. Thematic maps generated using the Regional GIS were used in storm water committee sessions to target problem outfalls or basins.
Another example -- Storm water pollutant loadings by watershed
were calculated by combining NCTCOG's detailed land use inventory
on the Regional GIS with event mean concentrations for 12 key
pollutants monitored through the regional program.
Figure 3
If the Standard Project Flood were to occur today, more than 12,000 homes and more than 140 million square feet of commercial property would be damaged, resulting in over $4 billion in flood damages and potential loss of life. NCTCOG's Regional GIS has the building footprint and estimated water level for each of these thousands of at-risk structures for many model flood scenarios.
NCTCOG is serving as facilitator for nine cities including Dallas and Fort Worth, three counties, and two special districts, under an interlocal agreement, in pursuit of a COMMON VISION for the Trinity River Corridor. The U.S. Army Corps of Engineers-partnered Upper Trinity River Feasibility Study is the largest cost shared study in the nation, and is addressing flood damage reduction, water quality improvement, environmental restoration, recreation and other allied purposes. The study operates under the direction of an Executive Committee of local elected officials and senior Corps Staff. A comprehensive Trinity River Information Network (TRIN) is being developed onto the Internet.
The Upper Trinity River Feasibility Study was initiated in 1990 to investigate the viability of structural and non-structural projects to address the potential for catastrophic flood damages along the Upper Trinity River Corridor through North Central Texas. The primary study area includes the cities of Dallas, Fort Worth, Arlington, Irving, Grand Prairie, Lewisville, Coppell, Carrollton, and Farmers Branch, jurisdictions that are at risk from flooding on the four main branches of the Trinity River as they flow through the Metroplex. A major task in the study has been the creation of new state-of-the-art computer floodplain and flood damage assessment models, which are used to help locate, evaluate, and quantify risks from potential flood scenarios. This analysis is also used to identify feasible alternatives. GIS technology has played a tremendous role in the development of these models and the presentation of the results to the participating local governments.
The development of the models began with the creation of extremely accurate (1 inch = 200 feet) basemaps, featuring 2-foot contours, extensive identification of structures, transportation facilities, hydrology, utilities, cross sections, and selected cultural, environmental, and recreational resources. Professional consultant services were utilized to fly the region, perform ground and GPS surveying, interpret the new aerials, and produce the digital database, both in Intergraph and Arc/Info Formats.
The detailed planimetric data was used by the Fort Worth District, U.S. Army Corps of Engineers to create a new HEC-2 model to predict water surface elevations along nearly 1000 cross sections spread across the 240 square mile study-area. The results of the HEC-2 model were used with digital elevation information in GRASS GIS software to produce an estimation of water depths across the study area under various flooding scenarios. This information was exported into ARC/INFO.
The depth information was converted and reclassified to produce a color-coded depth analysis, laid atop the digital mapping, in one-foot water depth intervals. This information was developed for 25, 100, and 500 year floods, as well as the Standard Project Flood, and examples will be demonstrated as part of the presentation.
By incorporating other planimetric data sources available at the NCTCOG, 76,000 individual building footprints that were mapped along the Corridor were assigned land use values and jurisdiction identification. The information developed in the depth analysis were applied to each of the 76,000 structures -- determining which flooding scenarios impacted them, as well as potential depth of water at each site. This enabled a statistical analysis of the number of structures impacted by flood, categorized by scenario (year), jurisdiction, and land use. This information has been displayed in tabular form, as well as by shading building footprints with specific colors based on desired categories (Figure 4). GIS technology is also allowing the linking of appraisal data to the individual structures, to better estimate the dollar value of flood impacts. This quantification of damages is vital to the determination of costs and benefits for proposed flood damage reduction projects.
The extensive effort to develop the detailed mapping data for the Trinity Corridor has resulted in other benefits to the region. Engineers are using the base information generated as the foundation for facilities planning throughout the Corridor. The detailed specifications of the data have been used by other cities as the specifications for their mapping projects, resulting in nearly seamless edge-mapping with the Trinity Corridor area. Many surveyors and developers are utilizing the ground monumentation generated and mapped by the study as the foundation for their work in and near the corridor. The Trinity River Project has not only served as a very effective model for the application of GIS technology for urban environmental needs, but it has served as a model for the generation of GIS data sets as well.
With detailed information available and with the significant advancements in computer on-line technology, NCTCOG is creating a detailed and thorough Internet information site for the Trinity River. At the center of much of this work is the development of a Trinity River "virtual tour." In its initial stages, the tour is being designed to provide access to information about specific sites of interest in the corridor and about flooding, which has been a primary focus of recent studies in the corridor. The "virtual tour" will provide a gateway to corridor cities, parks, mapping, statistics, river conditions, modeling, digital movies, and the Regional GIS itself.
With the significant work being done by local jurisdictions in the Trinity COMMON VISION program, and the numerous products of the Feasibility Study, the virtual tour is a significant opportunity to make information available to the many users of these resources.
Figure 4
The Trinity is an urban river in all respects. During the hot summer months, water is impounded in upstream reservoirs for water supply, resulting in a river greatly influenced by wastewater discharges that often exceed ninety percent of the river flow. Evaluation of projected flows and associated pollutant loadings is essential in planning to meet water quality goals for the river. With showers comes storm runoff carrying a variety of pollutants from lawns, pavements and a spectrum of land activities linked to 4.5 million residents in a highly urban matrix. Land use and demographic information analyzed using GIS capabilities help to characterize and estimate the impact of urban activities on water quality. When the big storm rolls in, attention shifts to major flooding and the devastating impact it has on life and property. With its member local governments and state & federal partners, NCTCOG is meeting the challenges of effective, cooperative, interjurisdictional. The Regional GIS, and the sharing of GIS-developed information through the Internet are each vital tools in the ongoing process of regional water resource planning and management.
Moore, A. W. ?, April 1927. "A Reconnaissance in Texas in 1846." Southwestern Hist. Quart., Vol. 30, #4.
North Central Texas Council of Governments (NCTCOG), 1971. Upper Trinity River Basin Comprehensive Sewerage Plan, Volumes I and II.
North Central Texas Council of Governments (NCTCOG), 1985. 1985 Annual Water Quality Management Plan for North Central Texas.
North Central Texas Council of Governments (NCTCOG), 1996. Annual Water Quality Management Plan for North Central Texas.
Promise, John; Brush, Samuel; Brooks, Chris and Brashear, Bob, 1993. Regional Urban Storm Water Management Strategy for the Dallas/Fort Worth Metroplex. Presented at APWA International Public Works Congress and Exposition, Phoenix, Arizona.
Texas State Health Department, 1925. Trinity River Sanitary Survey.
Texas State Health Department, 1959. Progress Report on Upper Trinity River Sewage and Industrial Waste Survey.
U.S. Army Corps of Engineers, Fort Worth District, 1990. Reconnaissance Report, Upper Trinity River Basin, Trinity River, Texas - Volume I - Main Report.
U.S. Army Corps of Engineers, Fort Worth District, and North Central Texas Council of Governments (NCTCOG), 1995. Information Paper - "A Benefit-Cost Analysis" - Main Document, Upper Trinity River Basin, Trinity River Basin, Texas.
1.
John Promise, P.E.
Director of Environmental Resources
North Central Texas Council of Governments
P.O. Box 5888
Arlington, Texas 76005-5888
Phone : (817) 695-9210
2.
Samuel W. Brush
Manager of Environmental Systems
North Central Texas Council of Governments
P.O. Box 5888
Arlington, Texas 76005-5888
Phone : (817) 695-9213
3.
Scott Rae
Environmental Planner
North Central Texas Council of Governments
P.O. Box 5888
Arlington, Texas 76005-5888
Phone : (817) 695-9219
4.
Sandy Blanchard
GIS Analyst
North Central Texas Council of Governments
P.O. Box 5888
Arlington, Texas 76005-5888
Phone : (817) 695-9238
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