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The old adage "let Nature take its course" is gaining more respect among engineers and scientists who are attempting to restore the complex ecosystems that evolved over millions of years only to be disturbed by humans in a blink of a geological eye. As the public recognizes the value of lost or degraded water resources, managers who face spiraling remediation costs are beginning to view the Earth's natural processes in a more practical light.
Special session presentations of the Hydrology Section at the AGU Spring Meeting in Baltimore showed how the evolving art and science of stream restoration is turning toward the multiple, interwoven threads of nature's ways. At the session Hydrological Restoration (H42E), presenters will demonstrate how the evolving art and science of stream restoration is turning toward the multiple and interwoven threads of nature's ways. "We're entering a phase where we're probably going to put more attention into restoring [streams] than developing them," said Ken Potter, an engineering faculty member at the University of Wisconsin and coconvener of the hydrological restoration session. Potter noted a few examples: restoring more natural flows to the Colorado River, returning meanders to the channelized Kissimmee River in Florida, and removing salmon migration barriers from rivers in the Pacific northwest.
"Restoration brings together topics from hydrology, geomorphology, and biology or ecology," said Potter. "Unfortunately, we don't have a long history of integrating that many sciences." The surface water management program in King County, Wash., probably furnishes a significant part of that brief history.
In the mid-1980s, teams comprising a planner, a biologist, an engineer, and a geologist surveyed flooding, erosion, water quality, and habitat problems in 29 drainage basins in the rapidly developing western part of the county for the Basin Reconnaissance Program. With the addition of a land use planner, hydrologist, and wetlands scientist in the late 1980s, the team analyzed drainage basin problems in more detail and designed solutions including capital improvement projects, purchase of critical land parcels, land use and drainage regulations tailored to conditions within each basin, and public involvement for over half of the 29 watersheds.
"King County's promotion of interdisciplinary teams, and especially the active dialogue between biologists and engineers, are key elements in the success of our stream restoration projects," said David Hartley of the King County Water and Land Resource Division in Seattle. "Additionally, local jurisdictions in Washington state benefit substantially from research conducted by the Center for Urban Water Resources Management at the University of Washington."
The knowledge gained from watershed research is not always used in stream restoration efforts, however. Under pressure from citizens and environmental groups, local governments are often prompted into immediate action to improve degraded streams. In many cases, however, "the practice is charging ahead of the science," Potter said. "The practices are not being well documented in the scientific literature, and we don't know [which practices] are good and which are not." "Probably very few local jurisdictions employ continuous hydrologic modeling or other techniques that examine the full spectrum of stream flow characteristics," said Hartley. "Also, there is often a reluctance to collect site-specific hydrologic data, which is often a very expensive error." Restoring stream function requires balancing channel and riparian characteristics with a suitable hydrologic regime.
Determining the hydrologic regime for a restoration project amounts to a crucial decision. In most cases, the cause of stream damage is land development, which decreases infiltration into the soil (and thus, base stream flows) and forces storm runoff into streams.
"The stream is reacting to disequilibrium," said Glenn Moglen, a civil engineering professor at the University of Maryland. "Philosophically, if you do nothing at all, the streams will find their new equilibrium and stabilize." The new channel will eventually become stable, but the stream habitat will differ dramatically from its predevelopment condition.
Moglen is graduate advisor to Kambiz Agazi, who used characteristics of stable streams with "natural" flow regimes as a yardstick for assessing the reliability of different channel reconversion projects in Maryland streams. While predicting the reliability (the inverse of the probability of failure) of three restoration projects during a year in which several major floods occurred, Agazi noticed a common characteristic that pointed to failure. If the channel depth was designed too deep, it allowed higher flow velocities that lead to scour and erosion.
According to Moglen, most hydrologists agree that undisturbed rivers naturally reach bank full-flow during a 2-year storm event. As the river floods and spreads out, pressure on the channel is relieved and flow velocity slows. Channels designed to hold maximum flows are doomed to failure, he said.
Planners are not necessarily stuck with postdevelopment hydrology, however. Hydrological disruptions imposed by development can be dampened by reducing high flows through stormwater control devices. King County planners used hydrologic modeling to simulate erosive flow durations, instantaneous peak discharges, and diminished summer base flows in one urbanized basin to assess different devices for retarding and storing storm water. Centralized storage and a high-flow bypass are effective and cost-efficient approaches, the model results indicated. In addition, the stream habitat will be improved by augmenting low summer base flows with groundwater pumped from a deep aquifer.
In many cases, the balance between surface water and groundwater that was upset by watershed development will need to be reestablished. For example, the Everglades is losing too much groundwater to the ocean because flood control measures radically altered its hydrology. Drainage of land near the east coast to protect Miami, Ft. Lauderdale, and Palm Beach from flooding created a steep groundwater gradient from the Everglades eastward. Because of the Everglades' high discharge of groundwater through south Florida's highly transmissive aquifer to the ocean, the vast, formerly marshy area retains just 50% of its original surface water. It has lost many wetlands.
Engineers at the South Florida Water Management District (SFWMD) are overseeing a long-term plan to partially restore predevelopment drainage and mitigate heavy nutrient loads to areas of the Everglades that lie north of the protected Everglades National Park. As a starting point, Randall Van Zee and colleagues are using the Natural Systems Model to estimate the Everglades' predrainage hydrology. The SFWMD has devised water management strategies that constrain the system to these more "natural" hydrologic conditions.
Biologists are comfortable with this model and are generally confident that ecological restoration will follow once a more natural hydrologic regime is restored. Using a large-scale hydrologic simulation model, senior engineer Cal Neidrauer and his colleagues are evaluating several restoration options that are integrated with water supply and flood control. For example, coordinating the system's water levels with antecedent rainfall conditions and weather forecasts (rather than a preset calendar schedule) is a potential operational improvement. However, the model results suggest that to achieve a satisfactory level of restoration, structural as well as operational changes are needed.
One such structural option, said Neidrauer, is to purchase a buffer zone between the Everglades and developed areas where higher water levels would be maintained to help reduce the groundwater gradient. Installation of underground seepage walls to retard ground water flow an unusual technology that has never been attempted before on such a large scale is also being considered. One concern is that the inhibition of groundwater flow might leave irrigation and drinking water wells high and dry during less rainy periods, said Neidrauer.
These dilemmas illustrate the competing needs for water. '"It's going to be a balancing act," said Neidrauer, "between water supply, restoration, and flood control." And having a place to live. Ironically, as suburban sprawl has transformed the landscape of drainage basins, King County's control over the land and its revenues to pay for restoration have been reduced.
"Today, the future of integrated watershed management depends increasingly on the ability of King County to partner with Seattle and expanding suburban cities to provide interjurisdictional, regional funding and participation in these programs," said Hartley.
With growing demands on local government funds, preserving stream environments may become "a question of striking the balance between public investment in restoration versus protection," said Hartley.
"Intuitively, we know that restoring a stream system is generally a lot more expensive than preventing damage to a functioning stream. Yet, fixing a problem stream often has a lot more political cache than protecting one that works, but has not yet been degraded by urbanization.
This dilemma can only be solved by public education and support for strict land use policies."
— Elaine Friebele