"That dirty old Trinity River sure has done me wrong
It came in my window and doors and now all my things are gone
Trinity River Blues keep me bothered all the time
I lost my clothes...believe I'm gonna lose my mind
They done built a levee, I have no more worry about
If that river should happen to rise
I'm gonna have to move my things out Trinity River rising, it came in my windows and doors."
- Blues song by Aaron "T-Bone"
Walker (1929)
This summer - as was the case in all too many previous summers - floods ravaged the Trinity River.
Record floodwaters (fed by intense rains in the first five months of 1990) made the Trinity River roar through the Dallas-Fort Worth area and then sweep downstream where it produced widespread flooding. Hardest hit was Liberty County downstream of Livingston Dam. The Red and Brazos rivers also spilled over their banks causing additional havoc.
The floods produced major damages. Roughly 6,000 individuals from 68 counties applied for federal disaster assistance. Only half of those counties (34) participate in federal floodplain management and flood insurance programs. Many homes and businesses were destroyed and, in the area below Livingston Dam, 200 homes were destroyed and 4,000 people were forced from their homes. Agricultural losses were estimated at up to $1 billion as crops were flooded before they could be harvested, topsoil was washed away, and livestock drowned. The impacts even reached Galveston Bay where the floods diluted saline water so much that oysters died.
How great were this year's floods? This year's floods set new records for high water on the Trinity river near Liberty, breaking those that were set before Livingston Dam was even built. At its apex, releases from Livingston Dam totaled 108,000 cubic feet per second (cfs). That's enough water to fill 1,200 swimming pools in less than a minute and to fill the Astrodome with water in only 12 minutes. Only a series of flood control dams held the floodwaters in check and kept the damages from being worse. This year's flood flows in downtown Dallas were 81,000 cfs (the third highest on record) with the dams in place. If the dams had not been there, Corps' officials say flows could have been greater than 260,000 cfs (the worst ever recorded in the Dallas area).
Are building flood control dams and other structures the best way to cut flood damages? Some critics say that structural measures like large dams provide a false sense of security that makes people feel they are safe from flooding. Structural measures are also expensive and can result in catastrophic losses if they fail.
Non-structural alternatives include managing existing water supply dams to mitigate floods during emergencies, preventing construction in low-lying areas, lessening the impacts of urbanization, and increasing the effectiveness of flood insurance and floodplain management programs.
Steps are being taken that could lessen potential flood losses. The Corps of Engineers, the North Central Texas Council of Governments (NCTCOG), and local governments are developing a holistic plan to manage the upper Trinity River. Studies are assessing the impact of floods depending on the amount of development that's allowed in low-lying areas. Development in the region's floodplain is being regulated by establishing uniform criteria. Harris County is building computer models to provide a better idea of how many homes and businesses have been built in low-lying areas. The Harris County Flood Control District requires new developments to include provisions to temporarily store stormwater runoff. The U.S. Geological Survey (USGS) is working with state agencies to improve models to simulate flows in the Trinity River basin and to identify high risk areas.
Dam building and dam management is being reviewed. Some politicians are calling for studies to see if more flood control dams (like the proposed Tennessee Colony project) are needed on the Trinity. State legislators have formed a task force to study if reservoir management strategies could be altered in the future to reduce flood risks.
Controlling Flood Losses
To understand why this year's flooding caused as much damage as it did, a number of basic issues must be explained and some misconceptions need to be clarified.
There are two ways to mitigate flooding. Structural measures include dams, channels, levees, stormwater drainage systems and other public works that manage stormwater runoff. Structural approaches have been widely used in Texas. Examples include flood control dams, widespread construction of levees to protect low-lying areas, improved channelization and drainage, and planning of huge tunnels to move stormwaters away from urbanized areas in Austin and San Antonio.
Some experts have recently criticized an over-reliance on structural measures because dams can fail in severe floods and levees may be overtopped by high water. Structural measures may also give people a false sense of security that encourages additional floodplain development.
On the other hand, non-structural measures are strategies that persuade people not to build in areas that are likely to be flooded . These include zoning and planning, tax incentives, flood insurance programs, relocation of buildings and communities, and other measures.
It first needs to be understood that not all dams are designed and/or operated to control flooding.
The federal government, through the U.S. Army Corps of Engineers, builds flood control reservoirs throughout Texas. The rationale is that flood control projects are in the broad national interest and wouldn't be economical for local sponsors to construct. Recent studies indicate that federal financing of flood control dams may no longer be financially viable (Wurbs, 1988). Many Corps of Engineers' projects serve many purposes and provide water supplies, recreation, and flood control.
Operating flood control reservoirs typically utilizes a strategy of leaving a set amount of storage empty to hold incoming floodwaters. Flood control dams usually release water more slowly than it's flowing into the reservoir. Otherwise, owners and operators could be charged with causing flooding before it would have begun if the reservoirs were not in place.
Water supply reservoirs are often built by local entities. Cities and others in need of water supplies typically sell bonds in exchange for a set amount of storage capacity. The goal in operating a water supply dam is to keep the reservoir as full of water as possible to guard against droughts. Unfortunately, if large amounts of water are stored in the reservoir, there isn't much room to buffer against floods.
During severe floods, the conflicting goals of water supply and flood control can become pronounced as they did during this year's flooding at Lake Livingston - a water supply dam with no flood control storage.
Those who have paid to develop water supplies don't want to release water prematurely or unnecessarily. After all, no one knows when floods end and droughts begin. Conversely, prereleases of water to make way for anticipated rainfall and runoff may ease the risk of minor flooding.
Factors That Increase Flood Risks
Urbanization ΓÇô the construction of buildings and the paving of sidewalks and streets - increases both the speed and the amount of runoff. Water that would usually soak into soils after a rainfall can't penetrate paved streets and parking lots. Instead, it just runs off, picking up speed as it goes.
Other aspects of urbanization also heighten the chance of flooding. Many cities in Texas have allowed extensive residential and commercial development in low-lying areas that are likely to be flooded. Many low-lying areas are typically referred to as 100-year floodplains. Typical rainfall and runoff should result in a 1% chance of these lands being flooded in any given year or once every 100 years. Just because a 100-year floodplain was flooded this year, that doesn't mean it's safe from flooding until 2090. Areas that are less likely to be flooded include 200-year and 500-year floodplains, while areas that are more likely to flood include 25- and 50-year floodplains.
The amount of construction that has occurred in low-lying floodplains isn't well known and this constitutes another part of the problem. Many areas of Texas do not regulate floodplain development. In some cases, local governments have only a rough idea of where development is taking place and don't discover problems until areas are under water. Some estimates suggest that Texas has 20 million acres of flood-prone property - the most of any State - and that 11% of the State lies within 100-year floodplains (Thomas, 1989). Roughly 1.3 million properties worth $55 billion are at risk from being sited in floodplains.
The impact of flood risks and floodplain management laws on land values is unclear. Recent floods may reduce land values and prospects for development. Some studies (Burby, 1988) suggest that strict enforcement of ordinances that limit development in floodplains lowers land values.
The Federal Emergency Management Agency (FEMA) estimates that roughly 675,000 households in Texas are located in flood hazard areas, yet 67% of may not be covered by federal flood insurance. On a national level, estimates suggest that the number of households located in 100-year floodplains has grown by 40% in the past 25 years, in part because more than 50 federal agencies encourage development in coastal areas (Milleman and Jones, 1989).
Studies by the Corps of Engineers have simulated the cumulative impacts of flooding in the Dallas-Fort Worth area based on different levels of floodplain development, and have evaluated the impact of structural and non-structural measures to reduce losses. The studies (Corps of Engineers, 1990) illustrate the impact of floodplain development on increasing flood risks.
The Corps evaluated current and future flood damages that could be caused by a standard project flood (a flood resulting from the worst rainfall that could be expected in a region). The studies compared the impacts of virtually uncontrolled development and floodplain management programs. Results suggest that damages from a major flood could total more than $11 billion if floodplain development is unregulated. A comprehensive floodplain management program could cut losses to $4 billion. If a major flood occurred now, four major levee systems in the area could be overtopped with high water and damages could be more than $3.7 billion.
To lessen flood risks, local governments have endorsed a corridor development certificate process to coordinate future development by requiring more stringent permit criteria. Structural and nonstructural ways of cutting flood losses are being identified. Computer models and geographic information systems that accurately reflect the impacts of new construction in floodplains are being developed.
FEMA's National Flood Insurance Program (NFIP) provides solutions to many of these problems. The NFIP identifies areas where flooding is likely and produces maps that display problem areas. NFIP provides flood insurance to local counties and communities that participate in the program and discourage unsound floodplain development. This includes land use management regulations, flood-proofing and elevation of existing structures, and other measures.
Many Texas counties and communities participate in the NFIP and Texas is third nationally in the number of federal flood insurance policies in effect (225,000). Texas also ranks second nationally in the number and amount of claims paid (55,862 claims have been paid for $575 million) and second in repetitive losses (Thomas, 1989).
Has FEMA has not done enough to discourage development in flood prone areas? Some studies say that the actual flood damage potential has increased by roughly 5%, even in areas that have floodplain management programs in place. Potential flood losses would have risen by 65% if floodplain management programs had not been utilized (Burby, 1988). More than $5 billion of flood insurance policies have been issued in high hazard zones that are especially vulnerable to flooding.
Other studies (GAO, 1988) suggest that more than 40% of the claims NFIP pays are for repetitive losses and more than $500 million has been paid for such claims (Milleman and Jones, 1989). More than half the losses were in coastal communities. Some critics allege that the NFIP provides incentives for individuals to increase their exposure to flood losses and increases floodplain development by providing insurance to those who build in low-lying areas (Burby, 1988). NFIP says that it discourages development in floodplains by charging higher premiums in those areas.
Another key issue is whether NFIP has the funds it would need to pay claims in a year when large numbers of natural disasters took place. A 1988 audit of the program (GAO) showed that a year of catastrophic flooding could result in losses of more than $4 billion even though current premiums total less than $500 million annually.
The Texas Water Commission is working with FEMA to help counties and communities carry out floodplain management programs. The community rating system, for example, cuts insurance rates when local governments lessen flood risks by preserving open spaces and not allowing development in floodplains, minimizing the impact of stormwater runoff, mitigating losses in often-flooded areas, and maintaining levees and drainage systems (Community Rating System, 1990).
