|
T.
<br /> orsuch Vatzonaz Wi4 deration v. Gorsuch 18 ERC 1109
<br /> d the epilimnion. When building a new dam. 4. Sediment
<br /> site preparation (e.g., removing organic Generally, large reservoirs act as sedi-
<br /> soils) can reduce future leaching. Once ment traps; the water velocity decreases
<br /> leted again, the record reveals neither the (compared to the upstream river) and
<br /> blem - number of dams for which mineral leach- sediment settles to the bottom of the
<br /> and = ing is a significant problem nor the cost reservoir. Thus, water released from the
<br /> )rmal of cure. dam will contain less sediment than up-
<br /> zero- 3. Temperature Changes stream water. This is generally viewed as
<br /> tom- In a thermally stratified reservoir, the an improvement in water quality. How-
<br /> iese, ever, the river will "tend to restore its
<br /> o be lower hypolimnion laver will generally be equilibrium [sediment) loading by scour-
<br /> !ser- colder than the upstream river, while the ing the downstream channel."t� Also, the
<br /> finer- f upper epilimnion layer will be warmer. reservoir will tend to fill with sediment,
<br /> )��,n_ Some species of fish can survive only in which in some cases can require periodic
<br /> the warm water; others can survive only in
<br /> dredging or sluicing. Dredging may tem-
<br /> )ster cold water. Thus, cold hypolimnion wa- poranly increase sediment load in the
<br /> ter, even if fully oxygenated, will harm or reservoir (and hence in the downstream
<br /> ems kill warm water fish but benefit cold water water); sluicing is a deliberate attempt to
<br /> Will fish; conversely, warm epilimnion water have the river carry accumulated sedi-
<br /> :ors, will harm or kill cold water fish and ment downstream.ls
<br /> era- benefit warm water fish. In some cases, Sediment release can be reduced by
<br /> tier. cold water discharo-es may be desirable—
<br /> n 1 careful dredging or by filtering. There is
<br /> on to create a trout fishery, for example. = no evidence in the record to suggest that
<br /> the also, colder water has higher capacity to increased sediment is a major probiem.is
<br /> •nds assimilate wastes, both because decom- 5. Supersaturation
<br /> r an position is slower and because oxygen is
<br /> rals more soluble in cold water.ts In short, when water plunges at high velocity
<br /> dams cause changes in the temperature of from the reservoir into the downstream
<br /> i downstream water, and some of the time, river, it becomes mixed with air. Depend-
<br /> ally but not all of the time, those changes are ing on the velocity and turbulence of the
<br /> the undesirable. falling water and the depth of the receiv-
<br /> de- ing basin, this can cause downstream
<br /> the Changes in the temperature of down- water to become "supersaturated" —
<br /> 11
<br /> stream water can be prevented in dams aerated in excess of normal concentra-
<br /> t in with multiple outlet levels by release of tion. Supersaturated water does not harm
<br /> ,try an appropriate mix of epilimnion and people and is suitable for most uses, but
<br /> ob- hypolimnion water. For some dams with- can be fatal to fish; documented fish kills
<br /> :ec- out multiple outlet levels, destratifying have occurred at a number of dams.t7
<br /> PA the reservoir may be feasible. However, Supersaturation can be prevented or
<br /> 46 the goal of maintaining downstream wa- reduced to nonfatal levels by reducing
<br /> •10 ter temperature, because it requires a mix the turbulence of the falling water (water
<br /> of warm and cold water, may conflict with released from a spillway at the top of a
<br /> 9ra the goal of maintaining downstream oxy- dam is more turbulent than water re-
<br /> ous gen levels. which calls for release of warm leased through a pipe in the dam), in-
<br /> unepilimnion water. creasing reservoir capacty to reduce the
<br />�e 12 See Trial Transcript, Nov. 3, 1980, at 125- need for spillway releases during flood
<br /> V 26 (testimony of Dr.James Whitley); Affidavit Periods, using a shallow receiving basin
<br /> fe of Steven Schatzow, Director, EPA Office of 1+Id
<br /> Quo, Water Regulations and Standards 112 (Feb. tb Id at 11,J.A. at 286 (effects of dredging);
<br /> 25, 1982), J.A. at 95, 101 (both noting that EPA Brief at 13-14 (effects of sluicing).
<br /> wrelease of epilimnion water would not be a 18 Plaintiffs'sole expert witness,Dr. Whitley,
<br /> try desirable solution to the low oxygen problem did not testify on the severity or prevalence of
<br /> !9 s below Table Rock Dam in Missouri because- sediment releases. Defendants' expert, Dr.
<br /> t the warm water would harm trout). Simons, testified that dredging was too expen-
<br /> �' 13 See Environmental Protection Agency, sive to be practical for large reservoirs, Trial
<br /> < Impact of Hydrologic Afodificat:ons on Water Quality Transcript, Nov. 4, 1980, at 68-69, 80-81, and
<br /> ? t 41 (1975) (EPA Doc. No. 600/2-75-007),J,k. that sluicing was rare, rd at 83-89.
<br /> 1; at 279, 291 [hereinafter cited as E'P,4 1975 Dam - 17 Joint Statement of Material Facts, supra
<br /> 0 Report]. note 4, 11, 23-29a,J.A.at 21-22.
<br />
|