Reducing Future Flood Losses: The Role of Human Actions: Summary of a Workshop, March 2, 2004, Washington, DC: A Summary to the Disasters Roundtable (2004)

Floods are the most frequent and damaging natural disasters. Inland flooding as the result of tropical cyclones causes more deaths annually in the United States than any other natural disaster, according to General D. L. Johnson, Director of the National Weather Service. Flood warnings and alerts are constantly improving in accuracy and timeliness, yet economic losses and human hardship due to floods continue to increase. The Disasters Roundtable organized a workshop to explore the role human actions play in contributing to destruction caused by floods (see Appendix A for workshop agenda). The content of this summary is based only on the contributions of participants in this workshop and is not intended to be an exhaustive summary of this topic.

Historically speaking, floods are part of the American culture and “great floods”—large floods that devastate a region and occur in every generation—often become pivotal events that change lives and landscapes. The most devastating flood in recent memory was the 1993 midwest flood. Damages from this flood totaled $15 billion, 50 people died, hundreds of levees failed or were overtopped and thousands of people were evacuated, some for months (FMRC, 1994). Although there are many other examples, the Johnstown, Pennsylvania flood in 1889 is another “great flood” in the United States.

Gerald E. Galloway, who has studied and influenced flood policy for over three decades, provided the following history and background of U.S. flood policies at the workshop.

Floods of the early 1900’s, such as the 1927 lower Mississippi flood, prompted the U.S. Congress to examine the appropriate role of the federal government in flood control. As a result, the Flood Control Act of 1928 and the Flood Control Act of 1936 were passed. These measures expressed “…the sense of Congress that flood control is a proper activity of the Federal Government” and that “…the Federal Government should improve or participate in improvements…for flood control purposes if the benefits to whomsoever they accrue are in excess of the estimated costs...” Under authority granted in these laws, the U.S. Army Corps of Engineers (USACE) assumed responsibility for building and maintaining flood control structures such as dams, levees, and other public works built to prevent rising waters from encroaching on the built environment.

In the early 1940’s, it seemed that engineered structures would be enough to minimize flood damage. However, Geographer Gilbert F. White and others, backed by extensive research, demonstrated that many engineered solutions were inadequate and in some cases

actually increased flood vulnerability (White, 1945). White suggested that instead of trying to control natural events we should learn to live more compatibly with the natural occurrence of floods. White advocated greater use of non-structural solutions to flood control such as flood proofing, elevation of structures, building restrictions, flood abatement zoning, etc. These ideas progressed and culminated in the 1968 National Flood Insurance Act a measure which provided federally backed flood insurance in return for communities implementing land use controls to promote wiser use of the floodplain. These and other measures helped policymakers make improvements in flood disaster relief programs and shift funding to non-structural programs, although many remained confident that engineered flood control was the best form of protection. Galloway noted in his remarks that in the case of the 1993 Mississippi flood, structural flood control reduced the damages by an estimated $18 billion, but the tradeoffs to the environment are difficult to assess

Flood control, in both structural and non-structural forms, helps protect lives and property from flood devastation. Floodplains are naturally occurring low-lying areas adjacent to waterways that act as natural filtration systems, serve as flood water storage sites, and help recharge ground water and aquifer systems. Structural flood control devices, such as dams and levees, have two major unintended consequences: 1) they alter nature significantly by not allowing the natural filtration, flood storage, and aquifer recharge and 2) they make low flat land that was previously in the natural floodplain more desirable for development. Thus, many forms of structural flood control protect lives and property, but they alter the natural environment. Also, engineering works have life spans of 50, 75, or 100 years and require maintenance, thus they are only temporary fixes.

Until the 1993 Mississippi floods there was very little recognition of these competing goals in the floodplain. Following these floods, policymakers questioned why they occurred. The answer Galloway stated was that major floods represent significant hydrometeorological events, i.e., “it rained a lot.” The real question is what can we do to reduce future flood disasters? Galloway concluded that major floods will continue to occur and those people living in the floodplain will continue to be at greatest risk. He also noted that climate change will likely affect the severity and duration of future floods and that many of the nation’s flood control structures are in poor shape.

Galloway offered the following policy issues and actions for consideration to alleviate flood disasters:

• Coordinate federal policy on flood and reconstitute the Water Resources Council or a similar body.

• Reduce flood damages and preserve and protect the natural environment, while remaining conscious of the need for sustainable growth and development.

• Share responsibility for floodplain actions by allocating costs to all levels of government and to the individuals who are at risk.

• Avoid developing the floodplain unless absolutely necessary.

• Minimize damages by restoring upland wetlands and improving agricultural practices (holding water where it falls), and through flood proofing, relocation of flood prone structures, land buyouts and acquisition of floodplain.

• Understand the uses and limitations of structures such as levees.

• Educate the public about the risks and costs of living in the floodplain.

• Treat the river basin as a complete ecosystem and consider flood damage reduction in this context.

He also included some challenges for the future, such as:

• Improve the National Flood Insurance Program by dealing with the issue of repetitive losses (explained later in this summary).

• Make development choices in coastal areas based on rational scientific judgments rather than on short-sighted political or economic considerations.

• Develop real-time mapping to fill the need for instantaneous information.

• Understand the implications and limitations of the national “100-year flood” standard.

• Coordinate water resource activities in the federal government.

• Support comprehensive planning that goes beyond an elected official’s term.

• Consider the issues of safety and human trauma resulting from flooding.

• Encourage collaboration among academic disciplines, such as engineering, social science, and other science and technology fields in solving flood damage reduction problems.

• Address policies that encourage doing the “wrong” thing.

A Presidential Disaster Declaration is a request made by a state governor for the U.S. President to declare that a major disaster or emergency exists, thus activating an array of federal programs to assist in the response and recovery effort (FEMA, 2004b). Many factors influence Presidents’ decisions to approve or reject the request of governors for disaster or emergency declarations, noted Richard Sylves, Professor of Political Science at the University of Delaware. The vast majority of presidential disaster declarations are for hydrometeorological events. Over the last 50 years, about 46.3 percent of declaration requests have been identified in the governor’s request for flood “primary incident” causes (Sylves, 1998). There may also be evidence of geologic factors in flood disasters. Ground subsidence, erosion, seismic activity that changes surface elevation and contours, and other geologic changes may increase flood frequency and vulnerability.

Human factors further complicate the analysis of flood disaster declarations. Human settlement patterns, population change, infrastructure effects, construction, and land use and landscaping practices, are among a long list of human factors that influence human vulnerability to floods. It is also complicated to assess human efforts to manage and respond to floods through a wide range of structural or non-structural measures.

Sylves explained that political factors sometimes influence presidential decision-making on whether to approve or turn down governor requests for declarations. Democracies work successfully when elected leaders associate their political welfare with responsiveness to public needs. Democratic theory assumes that government program administration involves public responsiveness and political motivations. Sylves reported that there is little evidence of partisan bias in the 50-year pattern of presidential approvals and denials of governor requests for declarations. There is also little evidence that presidents approve a greater number of governor requests during election years. Sylves noted that many governors know how to secure more declarations, and since 1988 governors stood a 3 in 4 chance that their declaration requests would be approved by the president. From 1953 to 1988, odds of approval were less than 2 in 3 (Sylves, 1998). Moreover, modern presidents face immense pressure by legislators and by non-federal officials to approve even marginal requests for presidential disaster declarations. Increased media coverage of disasters, especially by national broadcasts, is today a major intervening variable in a president’s “approve” or “reject” calculus.

Yet, according to Sylves, there are also administrative and public management factors. Generally speaking, emergency managers are now more professional, better educated, and more technologically capable, and post-disaster damage assessments are done more quickly and effectively than ever before. Changes in disaster law have expanded eligibility for declarations and for a wider variety of disaster causes. There are many more forms of government-provided post-disaster relief and aid available between disaster events than during previous decades. Flood mitigation has advanced correspondingly. However, as Galloway noted, generous government post-disaster relief and short-sighted floodplain management in many areas have created a sense that building in the floodplain is acceptable because the government will come to the rescue if flood damage occurs. The National Flood Insurance Program’s efforts and contributions have been substantial in improving land management and construction practices, but still many individuals, families, and corporations chose to accept significant flood risk.

Governments at all levels, often assisted by non-governmental organizations (NGOs), have roles in implementing policy for flood disaster loss reduction. On the national level, the U.S. Army Corps of Engineers (USACE) is charged with flood preparedness, mitigation, and recovery. The USACE currently furnishes experience, structure, and effective emergency response approaches. In the future, Harry Kitch, U.S. Army Corps of Engineers, proposed that “Silver Jacket Teams” be dispatched to provide states and localities a federally-integrated approach to long-term recovery assistance after a disaster. There are many agencies and programs involved in flood disaster response and recovery and the Silver Jacket Teams would create an effective mechanism to help integrate the assistance available. Kitch explained that these teams would provide more complete aid to communities and would advance social and economic recovery, as well as rebuilding or replacing physical infrastructure. He also

suggested that the Corps, other Federal agencies, and the states need to conduct broad, watershed (Level A) studies to help better define the national flood and storm risk, identify populations and areas at risk, elucidate types and frequency of critical events, and assist communities in their development of recovery plans.

According to Kitch, the nation suffers about $4 billion a year in flood damages. Urban expansion into floodplains continues at the rate of about 2 percent a year. High rates of population increase and development in coastal areas also continue. Development pressures and their corresponding benefits counterweight flood hazard risk, despite concerns about how new projects affect the natural environment. Kitch emphasized the need for more regional or community planning groups for disaster response and recovery.

The Federal Emergency Management Agency (FEMA, now part of the Department of Homeland Security, DHS) plays many roles in floodplain management. One of its main functions is to administer the National Flood Insurance Program (NFIP) and provide grants for mitigation and buyouts of flood prone properties. Congress created the NFIP in 1968 in response to the rising cost of taxpayer funded disaster relief for flood victims and the increasing amount of damage caused by floods. Flood damage is reduced by nearly $1 billion a year through partnerships with communities, the insurance industry, and the lending industry. Further, buildings constructed in compliance with NFIP building standards suffer approximately 80 percent less damage annually than those not built in compliance. And, every $3 paid in flood insurance claims saves $1 in disaster assistance payments (FEMA, 2004a).

Flood insurance is an integral part of a mitigation program. Currently, approximately 20,000 communities are part of the NFIP and National Flood Insurance policies total about $4.4 million, according to Clifford Oliver, Chief of the Risk Assessment Branch in FEMA's Mitigation Division, which is responsible for developing and implementing FEMA's Repetitive Loss Reduction Strategy. Approximately 110,000 policyholders have repetitive loss properties, which are defined as properties that have sustained four or more losses in a decade. Oliver noted that of these, approximately 11,000 have sustained four or more losses of $1000 or more. One percent of total base policies in effect produce an astounding 30 percent of claims payouts. Oliver indicated that about 750 properties join the repetitive loss category each year. Home elevation, demolition, and buyout are a few options that reduce repetitive losses. Relocation of structures to new sites is possible but often expensive. Some repetitive losses can be stemmed by relatively easy and inexpensive actions, such as elevating air conditioners well above ground level or flood proofing first floor areas. According to Oliver, FEMA has determined that mitigation action only moves about 250 properties out of the repetitive loss category each year. The program has yet to reach steady state status.

Although it is difficult to forecast which properties will become repetitive loss properties, FEMA is constructing a web portal to help make such determinations. An effort is being made to ensure that FEMA’s repetitive loss data is accurate to assist local officials in identifying these properties.

The NFIP was amended by Congress in June 2004 (Bunning-Bereuter-Blumenauer Flood Insurance Reform Act of 2004, P.L. 108-264). This law includes more money for mitigation and it extends NFIP to fiscal year 2008, but as Oliver noted, Congress has long been reluctant to give the executive branch a strong tool to address recurring flood loss policy claims. NFIP has only limited authority to penalize NFIP policyholders who experience repetitive flood loss and who refuse mitigation assistance, thus creating an unfair burden on all other policyholders.

Non-governmental organizations play an integral role in helping government officials develop floodplain policies. The Association of State Floodplain Managers (ASFPM) is an NGO with expertise in flood policy and floodplain management. The ASFPM engages in extensive outreach, education, and assists communities as they identify flood hazards, encourages the government to protect the natural and beneficial functions of floodplains, and strongly advocates government reform of flood policy and modernization of flood hazard maps to ensure the reduction of flood losses and the protection of the natural function of floodplains.

Current policy appears to permit intensive development in high risk areas, noted Larry Larson, Executive Director of the ASFPM. According to Larson, local authorities adopt flood hazard maps, advise property owners, and regulate development. Communities often ignore changing conditions and many disregard the impact that floodplain development has on other properties. Even when flood mitigation standards are implemented, flood damage continues to increase. Nevertheless, flood mitigation and wise development practices can make a difference.

Larson stated that “today’s floodplains are not necessarily tomorrow’s floodplains.” One of the biggest concerns is development in watersheds that paves over open land, resulting in an increase in runoff. This has the potential to promote more floods with greater destructiveness as well as the potential to increase the size of or reshape floodplains. ASFPM developed No Adverse Impact (NAI) floodplain management to encourage a change in flood policy in the United States. Larson believes that communities should not permit development that could potentially endanger others unless the impacts of that development are mitigated first. NAI considers how a change in the built environment affects other properties. In essence, No Adverse Impact floodplain management is where the action of one property owner does not adversely impact the rights of other property owners (ASFPM, 2004). “We have to ask ourselves if we are putting others at risk,” Larson said. The challenge is to define “adverse impacts.” Larson noted that ASFPM recently updated case law in this area related to community liability and “takings”, showing that communities are more liable when they permit development that adversely impacts others than when they fully assess the impacts and make development decisions based on potential consequences.

It is important to ensure that local officials understand what the likely impacts of new development will be and how they can mitigate flood aggravating effects of any proposed development. State executive orders that advance flood protection efforts in sub-state planning would help, as would changes in policy at the national level, according to Larson. Larson also maintained that the federal government has a tendency to furnish too much post-flood relief. This relief is often a palliative that discourages state and local officials from independently taking the tough and controversial actions to reduce flood vulnerability. He added that it is unfair for communities that do not belong to the NFIP to get infrastructure rebuilding aid (public assistance) from the federal government under presidential disaster declarations, but flood victims in these same communities cannot buy National Flood Insurance and cannot get individual assistance program help from the federal government.

What are society’s responsibilities in reducing flood losses? If you merely hold an insurance policy, have you adequately protected your life and property investment? The FM Global Insurance Company is the largest property insurer in the world and believes that insurance alone is not enough—it is better to prevent a loss rather than recover from one. FM Global representative Clive Goodwin noted that his company is in the business of prevention and mitigation and not just recovery claims payouts. FM Global conducts hazard assessments and promotes engineered solutions aimed at reducing risk. FM Global works closely with its customers so that they understand hazards. Together, FM Global and its customers devise scenarios through which a customer’s firm can practice how to get back up and running after a hazardous event. Goodwin remarked that FM Global is not interested in working with customers who choose to disregard hazard risks. Prevention and mitigation, according to Goodwin, are at the heart of what FM Global is all about.

Often FM Global’s recommendations appear commonsensical–move expensive equipment out of basements, rethink floor plans and inventory storage, engage in emergency pre-planning. As Goodwin explained, a mere six inches of flood water in a facility might be enough to interrupt business and cost a firm a substantial sum of money including future income. Goodwin noted that flood maps make it obvious which businesses are in floodplains, making it easy to identify their flood risk and determine which mitigation measures can help avoid losses in the event of a flood.

Many levees are not shown on maps and therefore businesses are often unaware that while their firms might be officially designated outside a floodplain, a levee failure puts them at risk for flooding under extreme conditions. Moreover, something as mundane as poor drainage and street flooding after a heavy rain could cause massive damage to building basements and first floors, including building contents. Jim Russell, Vice President for Outreach at the Institute for Business and Home Safety (IBHS), noted that flood abatement structures, such as levees and floodwalls, play a role in mitigation, but the nation faces a problem with respect to levee durability and adequacy. Most levees in the United States were built in the 1940’s with 50-year design life, thus many have outlived their life expectancy and

are in disrepair. Levees are built for a wide variety of reasons and many are privately owned or owned by special district governments. The organizations responsible for maintaining these levees range from well-managed, well capitalized, pro-active ones to poorly-managed, under-capitalized, passive ones. Yet, if you live in a jurisdiction participating in the NFIP and you reside behind a levee, you do not have to buy flood insurance. Russell noted that the Flood Risk Education Alliance (FREA) is a an example of a voluntary collaborative effort of federal, state and local agencies, insurers, non-governmental organizations and the private sector established to promote flood education and to spotlight the issue of levee protection. Information on how individual property owners and businesses can identify and evaluate their risk is provided on FREA’s website.

Tulsa, Oklahoma is a good example of a community with effective floodplain management and flood hazard mitigation. Ann Patton of Tulsa Partners explained that public and private sector officials in Tulsa formed partnerships intended to advance the Tulsa area’s flood mitigation efforts.

Tulsa’s past experience with frequent flooding led to recurring hardship. The response of Tulsa’s local authorities was to create a flood mitigation regulatory climate that encouraged private participation. Patton said that people came to understand that “everyone contributes to flooding in Tulsa, so everyone should pay something to prevent it”. In order for everyone to share the burden, the City of Tulsa charges a $4 per month drainage fee collected with water bills to support land management and maintenance of the stormwater drainage system for land acquired by the City. Once the city owns the land, it is used for a wide range of compatible activities and thus taken off the market for potential development.

Public participation was a major component in Tulsa’s planning efforts. Citizen advocates played a critical role in pressing for tough flood mitigation actions. For example, flood channel and river bank cleanups became common. Properties highly vulnerable to flooding were bought out or donated in an effort to eliminate structures in flood hazard zones. Experts in policy, planning and mitigation stepped forward and volunteered in the flood mitigation effort. Open space astride rivers and streams was preserved for public parks, recreation sites, and gardens. Detention basins, which are now local amenities and instruments of flood management, were built and old ones cleaned up.

Frequent flooding of the Arkansas River prompted Tulsa officials to develop a system of river parks to minimize the effects of recurring floods. The area now boasts 50

miles of scenic trails along the banks of the Arkansas River. Today floods pose fewer dangers to citizens of the City of Tulsa because of these mitigation activities.

Warning systems, stream gauges, mapping, and other related tools used to protect public safety are supported and maintained by federal agencies. For example, the National Weather Service—along with federal, state, and local partners—plays an important role in forecasting flooding events. The U.S. Geological Survey (USGS) collects data from stream gauges and provides timely assessments of river stages. In 2003, Hurricane Isabel hit the shores of North Carolina and moved north through the mid-Atlantic and parts of the eastern United States, and then into Canada. Six states and the District of Columbia were affected by hurricane and tropical storm flooding. Isabel was a success story for federal meteorological, river monitoring, and emergency management agencies as timely advisories and warnings were issued throughout the hurricane alerting citizens of the increasingly hazardous situation. Although property damage occurred, no deaths resulted from flooding during Isabel.

The USGS provides scientific and technical contributions to the study of land and water resources by collecting, compiling, and studying historic and real-time flood data. The Survey’s Robert Mason reports that USGS operates a stream gauging program that has 7,000 monitoring sites, 85 percent of which provide real-time information about many characteristics of streams and stream flows. The program costs about $120 million a year to operate and the burden of this cost is shared with state and local governments and other federal agencies such as the USACE and U.S Bureau of Reclamation.

Mason explained that the National Streamflow Information Program serves a wide variety of clients. The USACE, the Bureau of Reclamation, the Federal Highway Administration, the National Weather Service, FEMA and some 800 state and local agencies (many of them environmental agencies) rely on the program’s information. This information has many flood-relevant applications: reservoir operations, impoundment management, flood forecasting, inundation mapping, floodplain mapping, and evacuation planning, to name a few. Mason said streamflow information is made available via a website within an hour of original recording. By studying variability in flood flow, experts are able to produce, track, and refine new estimates of flood magnitudes for various recurrence intervals or frequencies, such as the 100-year flood, and to quantify land use or climatic factors that may be causing flood magnitudes to change. For example, the addition of the 1997 flood peak in a frequency analysis of the Cosumnes River in Northern California resulted in a 20 percent increase in the estimate of the 100-year flood for that stream. Furthermore, while records for the site date back to 1907, the 7 highest peak flows have all occurred in the last half of that record indicating trends are due either to land use or climate change.

During floods, streamflow measurement is often extremely difficult, but USGS is employing new technologies to improve measurement efficiency and timeliness. Mason explained that USGS now uses hydro-acoustics technology to measure flood flows in streams

in a fraction of the time that traditional mechanical current meters once required. Similar to sonar, these technologies measure the “Doppler shift” in the frequency of sound reflected off of sediment and other materials suspended in the flowing water. The same technology can also be used to infer suspended sediment concentrations and the concentrations of some metals that attach to the sediment. The USGS is also experimenting with radar technology, particularly microwave radar, to measure stream velocities. These velocity measurements can be coupled with measurements of channel depth and area obtained with ground penetrating radar to measure flow. The radar instruments have been attached to helicopters to take flow measurements by flying over the river.

The USGS is working to develop new internet-related methods to disseminate streamflow flood data in a more user-friendly manner. New geographic web portals help put current flow conditions, including floods, into historic context so affected citizens can act to protect life and property. Real-time flood mapping is now possible and will be useful to emergency managers, floodplain managers, and others. Mason noted that the USGS expects to continue to make constant improvements in flood frequency analysis.

FEMA’s Multi-hazard Flood Map Modernization program is a $1 billion, five-year effort, according to Michael Howard, Federal Emergency Management Agency/DHS. A major goal of the program is to create one system from which everyone observes the same data. FEMA is developing a web portal that will provide open access to maps and data to help users better understand flood hazards. FEMA is decentralizing the process of data collection and working to understand state and local mapping needs. The portal created by the map modernization program will ultimately help reduce spending on flood emergencies and alleviate some of the burden on states and localities with respect to the collection of data and the coordination of data management. The effort employs common standards that will make it possible to harmonize, pool, and reuse data. Moreover, the project will use digital layers—including special flood hazard zones, land areas, stream level, and surface and aerial projections.

FEMA’s web portal will provide the public with access to digital flood-relevant maps, which can help in assessing hazards and making land management decisions. Making maps available online also reduces requests for and costs of paper map distribution. Making GIS map data available online will be an extraordinary contribution to those engaged in flood mitigation.

Map modernization will help address repetitive loss issues by ensuring that flood-prone areas are identified before the flood. The improved flood data will also help those responsible for the protection of critical infrastructure.

The National Oceanic and Atmospheric Administration’s (NOAA’s) role in reducing flood losses includes maintaining a web interface that provides access to real time observations, weather and water forecasts, and severe weather watches and warnings. Utilizing a spectrum of dissemination mechanisms, this information is provided to partners and customers and contributes to mitigating the impact of flood events. According to NOAA scientist and hydrologic services manager Thomas Graziano, NOAA strives to provide government officials, the private sector, and the general public with credible warnings with the longest possible lead-times. NOAA is modernizing its hydrologic services program

through the implementation of the Advanced Hydrologic Prediction Service (AHPS). AHPS is a 10 year, $60 million dollar program that, when fully implemented, will yield a $766 million dollar annual benefit from improved long-range forecasting. AHPS service enhancements include the provision of flash flood alerts through seasonal forecasts, the quantification of forecast certainty, visually-oriented products, flood forecast area mapping, and more accurate and timely forecasts and warnings. By presenting more of its work in a visual format, NOAA is helping people to better understand the information, recognize the threat posed, and act accordingly on that information.

NOAA interlaces precipitation data, river gauge information provided by the USGS and others, weather forecasts, climate prediction analysis and more. This information is collected from terrestrial-, aerial-, and satellite-based sources. NOAA’s work facilitates better precipitation estimates, superior run-off modeling, more accurate hydrological predictions, improved watershed modeling, and enhanced flood forecast modeling. The sophisticated integration of these information sources through AHPS permits users to develop “custom fits” of their local information with more broadly collected NOAA information. Graziano reported that NOAA will implement AHPS at over 3,500 river forecast locations nationwide.

NOAA coordinates its efforts with other federal agencies, for example, the USGS and NOAA have held joint quarterly hydrology committee meetings for the past three decades. NOAA participates in a joint annual coordination meeting with the USACE and the USGS, and also participates in annual policy and technical coordination meetings with the Natural Resources Conservation Service (NRCS). Moreover, NOAA is a federal member of the Advisory Committee on Water Information (ACWI) and coordinates quarterly with a spectrum of federal and private water agencies through ACWI’s Subcommittee on Hydrology. NOAA expects to continue to make important and far reaching contributions to efforts aimed at flood loss reduction.

In Houston, Texas each new flood seems to be proclaimed as “the worst flood ever,” according to Professor George Rogers of Texas A&M University. Having heard these claims, Rogers began researching whether flooding is truly getting worse, and if so, whether there is a correlation between flooding and land development patterns. In addition, he wanted to determine whether flood mitigation efforts have been effective. In order to do this, Rogers chose to study the White Oak Bayou of the San Jacinto River northwest of Houston in Harris County. He collected daily flow information, precipitation data, historic records on flow levels, and annual land development information. Data on every developed land parcel in Harris County was taken into account. Extensive modern human settlement in the study area began in 1894 and moved up the basin along riparian corridors. Rogers applied GIS techniques to develop cumulative measures of impervious cover, total developed areas, drought and flood impacts, and more.

Rogers went through a series of model types and finally settled on a model that considered rainfall before, during, and after flood events. He found in his statistical correlations that loss of natural areas played a role in flood severity, as did the construction of roads (often overlooked in flood mapping). Soil types, particularly impervious soils, slopes or gradients, as well as slow running water, played a role. The total watershed area remained constant as new land was developed. Gradually, there was a fill-in of space so that edges between developed areas were reduced.

Major floods took place in the study area in 1836, 1926, and 1936. The Harris County Flood Control District was formed in 1937 after the 1936 flood. Rogers found that the District channelized streams for flood control, which worked well until six inches of rain fall in a 1972 flood event causing more damage than 16 inches of rainfall did in 1936. In the aftermath of the 1972 event, authorities adopted new flood mitigation measures, new drainage criteria, and more detailed flood maps. However, Rogers reported that these post-1972 flood control activities did little to slow or reverse the pattern of worsening flood devastation. In the area of study, development and population growth was so great that it undercut the benefits of flood mitigation. In effect, Rogers found that flood mitigation was too little, too late. He stated that watershed planning did little to stem the increase of impervious cover mainly because the area experienced exponential population growth.

The question remains, how can flood damage potential be reduced in White Oak Bayou? Rogers suggested that the county impose severe restrictions on development activities that would limit impervious cover to only 10 percent of the land area of the watershed. Rogers recommended that developed areas be limited to 25 to 33 percent of the area of watersheds like White Oak Bayou. He suggested that more development be moved out of riparian areas and away from streams, and that changes be made in transport modes because new roads often re-channel streams in unsafe ways. He advised that planned communities be built so that they are compatible with the dynamics of the watershed and suggested developing models that make possible sub-watershed analysis and testing of different approaches to mitigation.

Rogers maintained that little can be done to stem population growth in the area, but certainly development needs to progress vertically so that as much open space as possible is left undeveloped.

Despite improvements in science and technology that have given us better warnings, maps, monitoring instruments, and improved analysis, vulnerability to flood disasters has increased, mainly due to population growth and development in risk-prone areas. Major problems related to flooding still exist: $4 billion in annual flood damages continue, urban expansion into floodplains continues at about 2 percent per year, and rapid population growth into coastal areas continues. In many areas, development pressures in flood hazard zones increase seemingly irrespective of known flood risk. Are our policies encouraging

growth in the wrong places? Are we exacerbating flood disasters by attempting engineered solutions? These questions will be examined and re-examined in the future.

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