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Biological Opinions - Bureau of Reclamation

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4. Removal <strong>of</strong> Small Dams (permanent and flashboard)<br />

a. Project Description<br />

The CDFW Restoration Manual does not cover the removal <strong>of</strong> small dams, however guidelines<br />

and minimization measures have been developed in this proposed action. Types <strong>of</strong> small dams<br />

are permanent, flash board, and seasonal dams with the characteristics listed below.<br />

Implementing these types <strong>of</strong> projects may require the use <strong>of</strong> heavy equipment (e.g., selfpropelled<br />

logging yarders, mechanical excavators, backhoes). Dams removed in part or in<br />

whole, by the use <strong>of</strong> explosives are not included in the proposed action.<br />

Dams included in the Program are defined by the California Division <strong>of</strong> Dam Safety (California<br />

Water Code, 2010):<br />

Any artificial barrier which either (a) is less than 25 feet in height from the natural bed <strong>of</strong><br />

the stream or watercourse at the downstream toe <strong>of</strong> the barrier, or from the lowest<br />

elevation <strong>of</strong> the outside limit <strong>of</strong> the barrier to the maximum possible water storage<br />

elevation or (b) was designed to have an impounding capacity <strong>of</strong> less than 50 acre-feet.<br />

In addition, this Program will only include dam removal that will form a channel at natural grade<br />

and shape upstream <strong>of</strong> the dam, naturally or with excavation, in order to minimize negative<br />

effects on downstream habitat. Dam removal projects will (1) have a relatively small volume <strong>of</strong><br />

sediment available for release, that when released by storm flows, will have minimal effects on<br />

downstream habitat, or (2) are designed to remove sediment trapped by the dam down to the<br />

elevation <strong>of</strong> the target thalweg including design channel and floodplain dimensions. This can be<br />

accomplished by estimating the natural thalweg using an adequate longitudinal pr<strong>of</strong>ile (CDFW<br />

Restoration Manual Part XII Fish Passage Design and Implementation) and designing a natural<br />

shaped channel that provides the same hydraulic conditions and habitat for listed fish that is<br />

provided by the natural channel and has the capacity to accommodate flows up to a 2-year flood.<br />

b. Minimization Measures<br />

<br />

<br />

<br />

All construction will take place out <strong>of</strong> the wetted channel either by implementing the<br />

project from the bank and out <strong>of</strong> the channel or by constructing c<strong>of</strong>fer dams, removing<br />

aquatic species located within the project reach, and dewatering the channel.<br />

No more than 250 linear feet (125 feet on each side <strong>of</strong> the channel) <strong>of</strong> riparian vegetation<br />

will be removed. All disturbed areas will be re-vegetated with native grasses, trees, or<br />

shrubs.<br />

All dewatering efforts associated with small dam removal will abide by the applicable<br />

minimization measures (Section D. Sideboards, Minimization Measures, and Other<br />

Requirements).<br />

c. Data Requirements and Analysis<br />

A longitudinal pr<strong>of</strong>ile <strong>of</strong> the stream channel thalweg for at least a distance equal to 20<br />

channel widths upstream and downstream <strong>of</strong> the structure and long enough to establish<br />

the natural channel grade, whichever is farther, shall be used to determine the potential<br />

for channel degradation (as described in the CDFW Restoration Manual).<br />

518

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