Environmental Engineering Reference
In-Depth Information
salmon would eventually need some way of getting back up past the dam and into
their home water, their spawning grounds. So, the scientists and engineers devised
and installed fish ladders in the dam so the salmon could climb the ladders, scale the
dam, and return to their native waters to spawn and die.
After a few seasons, the salmon again ran strong in the Rachel River. The sci-
entists had temporarily—and at a high financial expenditure—solved the problem.
Nothing in life or in nature is static or permanent. All things change. They shift from
static to dynamic, in natural cycles that defy human intervention, relatively quickly,
without notice—like a dormant volcano, or the Pacific Rim tectonic plates.
After a few years, local Rachel River residents noticed an alarming trend.
Studies over a 5-year period showed that no matter how many salmon were released
into the river, fewer and fewer returned to spawn each season. So they called in the
scientists again. And again they thought, “Don't worry. The scientists will know.
They'll tell us what to do.” The scientists came in, analyzed the problem, and came
up with five conclusions:
1. The Rachel River is extremely polluted from both point and nonpoint sources.
2. The Rachel River Dam had radically reduced the number of returning
salmon to the spawning grounds.
3. Foreign fishing fleets off the Pacific Coast were depleting the salmon.
4. Native Americans were removing salmon downstream, before they even got
close to the fish ladder at Rachel River Dam.
5. A large percentage of water was being withdrawn each year from rivers
for cooling machinery in local factories. Large rivers with rapid flow rates
usually can dissipate heat rapidly and suffer little ecological damage unless
their flow rates are sharply reduced by seasonal fluctuations. This was not
the case, though, with the Rachel River. The large input of heated water
from Rachel River area factories back into the slow-moving Rachel River
was creating an adverse effect called
thermal pollution
. Thermal pollution
and salmon do not mix. First and foremost, increased water temperatures
lower the dissolved oxygen (DO) content by decreasing the solubility of
oxygen in the river water. Warmer river water also causes aquatic organ-
isms to increase their respiration rates and consume oxygen faster, increas-
ing their susceptibility to disease, parasites, and toxic chemicals. Although
salmon can survive in heated water—to a point—many other fish and
organisms (the salmon's food supply) cannot. Heated discharge water from
the factories also disrupts the spawning process and kills the young fry.
The scientists prepared their written findings and presented them to city officials,
who read them and were initially pleased. “Ah!” they said. “Now we know why we
have fewer salmon!” But what was the solution? The scientists looked at each other
and shrugged. “That's not our job,” they said. “Call in the environmental folks.”
The salmon still ran, but not up the Rachel River to its headwaters.
Within days, the city officials hired an environmental engineering firm to study
the salmon depletion problem. The environmentalists came up with the same
causal conclusions as the scientists, but they also noted the political, economic, and
