Passive Restoration

How Does Urbanization Affect the Watershed?

How Do Dams Affect the Watershed?

How Does Agriculture Affect the Watershed

Passive restoration means allowing natural processes to return to a stream by stopping activities that cause degradation or prevent recovery.^{(Kauffman et al. 1997)} "Active" restoration refers to manipulating the ecosystem to re-establish the desired function.

Improving land management and letting nature do the repair is often more effective than trying to compensate for the damage. Passive restoration includes changing land use in the watershed to prevent soil erosion and increase water infiltration; managing cattle to protect riparian vegetation and streambanks; keeping toxic chemicals out of the water; managing construction, timber harvest, and roadbuilding to prevent sedimentation; and choosing not to build, harvest, or graze in sensitive areas.^{(Kauffman et al., 1997)}

Most fish consumption advisories in the US concern mercury, PCBs, dioxins, chlordane, and DDT levels in fish. Approximately 30 fish advisories were issued in the states of Washington, Oregon, and Idaho in 1996.^{(Kyle, 1998)}

It is often less expensive to prevent further damage than to repair what has been done. Therefore, the first priority for city planners, developers, and residents is to gain an understanding of local watersheds and shape new land uses appropriately. The following recommendations or measures are being taken in the Portland metropolitan area. They have applicability to towns and cities everywhere.¹⁸

Dams capture and hold sediment and organic material, blocking the flow of nutrients downstream and causing higher levels of erosion and other changes to the river channel for miles below the dam. Dams alter the temperature regimes of naturally flowing rivers; stream temperatures are higher for a longer period in the summer and lower in the winter. Shifts in temperature regime can change the timing of salmon incubation and spawning, reducing life history diversity. Loss of diversity makes a population more vulnerable to environmental change.¹⁹

Dams used for flood control, irrigation, hydropower, and recreation also alter the natural patterns of high and low water (the hydrograph). Salmon migrations, both upstream and downstream, are closely correlated with flow. Changes in flow can put migrants in the wrong place at the wrong time. For example, juvenile salmon depend on river energy to migrate passively downstream tail first. If they do not reach saltwater at the proper time and size, they may fail to adapt physiologically and may suffer higher mortality from disease or predators. Juvenile salmon are estimated to take more than twice as long to reach the Columbia River estuary since the mainstem dams were constructed.^{(CBFWA, 1991)}

Fluctuations in daily river flows caused by daily changes in power demands can strand juvenile fish in pools near shore, where they die from heat stress, predation, or desiccation. In a recent study of stranding in the Hanford Reach conducted by Washington Department of Fish and Wildlife and Grant County Public Utility District, biologists counted 31,500 dead juvenile salmon in the limited areas they sampled.^{(WDFW, 1998)}

A percentage of juvenile fish traveling downstream are injured or killed passing through turbines. Others are injured or killed going through bypass facilities. Studies have found that each dam with fish passage on the mainstem Columbia and Snake kills between 5 and 17 percent of the migrants.^{(Marmorek et al., 1996)}

Snake River salmon are removed from the river at Lower Granite Dam, put into trucks or barges, transported past the next eight dams, and released below Bonneville Dam to continue their journey to the sea. Transportation entails some mortality. It is likely that transportation also interrupts or compromises the physiological changes juvenile fish undergo as they migrate, impairing their ability to fully adapt to salt water. They are more exposed to predators upon release from the barge or truck, when they are unnaturally concentrated in one place. ^{(ISAB, 1998;) (Petersen and De Angelis, 1992)}

Downstream migrants have the best chance of survival by passing over the dams in controlled spill or surface bypass systems. Mortality estimates for passing through spill, turbines, or a screen system were 4 percent, 18 percent, and 20 percent, respectively, in the only comparative study done so far.^{(Gilbreath et al., 1993)} A potential hazard of spill is the tendency of falling water to capture air, supersaturating the river with dissolved gas. This can cause air bubbles in the fish bloodstream, similar to "the bends" of divers who ascend too quickly. Recent engineering changes to the mainstem dams, including spill deflectors or "flip lips," and others under development, such as raised stilling basins downstream, have reduced this problem.

It is widespread scientific consensus that salmon need natural river conditions to complete their life cycle and survive for generations to come. ^{(ISG, 1996; NRC, 1996)} Operating dams to follow the natural river hydrograph more closely would reestablish some of the ecological functions of the river and would assist salmon migration. Minimizing daily fluctuations in flow during periods of egg incubation, emergence, and early life of salmon fry would improve survival.

Adult passage over dams can be improved by engineering changes based on bioenergetic studies of salmon. Some studies indicate that adult salmon lose less energy from leaping over vertical barriers than from swimming through submerged weirs and baffles.^{(Orsborn, 1987)} This suggests that if fishways are correctly designed, adult salmon could negotiate high dams such as Grand Coulee and Brownlee, which do not now have fish passage, and reclaim hundreds of miles of former habitat.

These "pushup" dams often block fish passage entirely. When they are breached, the resultant rush of sediment and gravel downstream can destroy spawning beds. Yearly disturbance of the stream channel can create many unintended consequences for banks and substrate.²⁷

When the soil is exposed and compacted or heavily eroding, water runs off more rapidly and carries more sediment to the streams. The net result is an altered hydrograph, with higher peak flows and lower low flows. This means bigger floods, less riparian vegetation, and less salmon habitat. Excessive sediment clogs spawning gravels, fills in pools, and alters channel width and mean depth.^{(Mount, 1995)}

Agricultural chemicals have a substantial effect on both surface water and groundwater. Recent US Geological Survey (USGS) studies of water quality and fish communities in the central Columbia plateau, for example, found nitrate concentrations exceeding drinking water standards in about 20 percent of the wells sampled.^{(USGS, 1998)} The highest concentrations were generally in shallow wells in irrigated areas, and were attributed primarily to agricultural fertilizers.

Pesticides were detected in 60 percent of shallow wells and 46 percent of deeper public supply wells, also correlated with irrigated agricultural areas. High levels of pesticides, including DDT, also were detected in fish tissues in the Yakima River Basin, one of the most intensively irrigated areas in the United States.^{(USGS, 1997)} These levels were high enough to pose a risk to human health from eating fish from the lower Yakima River. The Washington Department of Health issued an advisory warning against eating bottom fish (large-scale sucker, bridgelip sucker, mountain whitefish, carp, channel catfish, and northern pikeminnow) from the lower Yakima River more than once a week because of high levels of DDT found in their tissues.³¹

Water-conserving irrigation methods can make a big difference in soil erosion and the discharge of sediments into the streams. A USGS study of water quality in the central Columbia plateau^{(USGS, 1998)} found less suspended sediment and lower concentrations of DDT in streambed sediment and fish tissue in areas where sprinkler or drip irrigation predominated. "For nine drainage basins sampled in 1994, average daily yields of suspended sediment . . . . ranged from 0.4 pound per acre from a basin with no furrow irrigation to about 20 pounds per acre from a basin where about 60 percent of cropland is irrigated by the furrow method," the study states.^{(USGS, 1998)}

Many agricultural practices in common use can dramatically reduce erosion, including the following.^(NACD)

A landmark study by the National Research Council reported that "alternative" agricultural methods could be as successful and profitable, for small or large farms, as "conventional" methods.^{(NRC, 1989)} The difference is that alternative systems reduce synthetic chemical inputs (pesticides, fertilizers, and antibiotics), and "more deliberately integrate and take advantage of naturally occurring beneficial interactions" to raise healthy crops.

Alternative systems may require more information and more intensive management because it is necessary to balance and incorporate "natural processes such as nutrient cycles, nitrogen fixation, and pest-predator relationships into the agricultural production process. . . . The objective is to sustain and enhance rather than reduce and simplify the biological interactions on which production agriculture depends, thereby reducing the harmful off-farm effects of production practices."^{(NRC, 1989)}