Ecologicalenvironmental Consideration Of Dam Operation

The following observations are generalized from the literature at large. Whether any particular concern applies to any particular dam is a function of a suite of factors that might include the dam's type (e.g. concrete or earth), its purpose (e.g. hydrologic regulation, hydroelectric generation, tailings impoundment), its size, location and operating protocol (e.g. timing of drawdowns, epilim-netic versus hypolimnetic draw, peaking versus base load generation, etc.). Finally, The observations are derived from an ecocentric rather than any anthropocentric ethical premise, that is a rather uncompromising ecological view of the relationship between nature and humans.

The ecosystem approach can work for dam owners/operators to a greater extent than they may perceive it to be working against them. Here, the Physicochemical effects (physical or chemical factors) have separated from biological effects. Generally changes in the biological community are driven by changes in the physical or chemical (physicochemical) dimensions of the habitat (niche).

Impacts are also organized spatially as those that occur: (a) downstream of the dam,(b)within the water column of the reservoir/impoundment, (c) at the sediment/water interface (which may or may not feed into the water column) and (d) a category for impacts that act outside the immediate dam/reservoir system. These latter impacts might be viewed as externalities with less relevance for operators. In any event, the evidence for external impacts is substantially weaker than that for a-c.

Downstream impacts could include changes in Physicochemical factors and Community structure. The physicochemical factors are: temperature, oxygen content, water chemistry, particulate loading, transparency, discharge patterns, flow rates/shear and channel simplification. The community structures are: environmental conditions exceed tolerance limits of original community members, species richness, genetic diversity, productivity and feedback.

Water column impacts could include changes in Physicochemical parameters and Community structure. The Physicochemical parameters consists of temperature, oxygen content, water chemistry, transparency, morphometry, internal seiches and altered currents. The community structures are longer migration times, environmental conditions exceed tolerance limits of original community members, productivity, diversity and feedback.

Sediment impacts could include changes in Physicochemical parameters and Community structure. The first one consists of temperature, oxygen content, light, remineralization, compression and sedimentation. The second one consists of environmental conditions exceed tolerance limits of original community members, species richness, productivity and feedback

Externalities could occur at a variety of scales and might include Local, Regional or Global externalities. The local externalities can cause riparian losses, hydrologic budget, habitat fragmentation. The regional externalities can cause climate change while the global externalities can cause climate change and orbit dynamics. These externalities could lead to loss of biodiversity and decreasing ecological integrity.

Dams can be operated in ways that decrease their environmental impacts. Recent examples include the installation of a selective water withdrawal system on the Hungry Horse Dam and the (initially seredipitous) drawdown at Glen Canyon. Doing so requires increased communication and trust among engineers, ecologists and other professionals in order to properly bound the problem. Engineers need to evaluate the extent to which regard for the environment is codified as good practice. There will have to be a willingness to experiment (e.g. demonstration projects) with a commitment to redefining operational technical directives as new knowledge emerges ( e.g. optimal performance standards might equate ecological integrity with revenue generation).

Ecological integrity (the genetic diversity, species diversity and ecological diversity that maintains the flows of energy and materials through ecosystems) is the key mechanism for adapting to changes in environmental conditions through evolutionary change. Protecting diversity means protecting habitat, not only against loss but against fragmentation.

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