Riparian Resources for Aspinall PDEIS

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woody vegetation on 55 to 65 percent of the bottomland. The preimpoundment period used in this analysis was typified by drier periods and scour during that 31 year interval prevented woody vegetation from colonizing 40 percent of the bottomland. The 31 year preimpoundment condition did not have an interval exceeding 3 years without a flow that removed woody vegetation from at least 50 percent of the bottomland. The No- Action alternative has an 8 year interval, a 9 year interval and a 10 year interval without a flow that removed woody vegetation on 50 percent of the bottomland. Impacts of operations governed by the No- Action will be long -term duration. Action - alternatives A through b are each characterized with an 8 year interval, a 9 year interval and a 10 year interval without a flow that removed woody vegetation on 50 percent of the bottomland. Impacts of operations governed by the action - alternatives will be long- term in duration. INTENSITY: The No- Action reduces the percentage of bottomland cleared by shear by 63 percent and is of major intensity. Each action - alternative is increase the percentage of bottomland cleared by shear with respect to the No- Action. Operation governed by action - alternatives A through b each will have a moderate increase on woody vegetation removal by scour. TYPE: Operations under the No- Action and each of the action- alternatives is adverse with respect to protection of bottomland riparian resources. CONCLUSION: Conclusions are summarized in Table 2. Operation governed by the No- Action alternative can be expected to have a regional scale, long -term and major intensity impact to Black Canyon riverine resources. Continuation of operation by the No- Action would result in irreversible encroachment of woody vegetation and an overall adverse impact to Park resources. Operations governed by the action - alternative A can be expected to have or action - alternative A can be expected to have a local -scale improvement on the regional -scale impact of the current operation. The long- duration of the operation and moderate intensity improvement is still expected to result in irreversible encroachment of woody vegetation and the type of the impact is adverse. Operations governed by action - alternatives B or C can be expected to local -scale improvement on the regional -scale impact of the current operation. Operation under action- alternatives will have a long -term impact on park resources; the duration of successive intervals without a shearing flow is too long. The intensity is moderate. Moderate intensity improvement coupled with the long-term duration is not sufficient to preclude the encroachment of woody vegetation and the type of response is adverse.