Alternatives Comparison. Under Alternative D, no construction would occur and there would be no impacts to soils, hydrology, vegetation, wildlife, or recreation. However, the existing culverts would remain the only means of controlling stormwater runoff down Tuacahn Wash and the developments at the mouth of Padre Canyon would continue to be at risk from flooding, causing potential damage to property, possible injuries, and costly remediation measures. Implementation of Alternative D could have major socioeconomic impacts (Table 3). With the exception of the access route, Alternatives A and B are identical. Under Alternative A, the access road would be 1,700-feet long and would occur largely within Tuacahn Wash. Under Alternative B, the access road would be 650-feet long and would occur straight from Tuacahn Drive, directly east to Tuacahn Wash. Unlike the access road under Alternative A, this road would require crossing and piping of three natural washes, and fill may be required to provide a flatter driving surface to support heavy equipment. Although the Alternative B route is shorter, it would require more involved construction for access than Alternative A because the area of disturbance is more densely vegetated and spans more natural land contours than access through the existing wash under Alternative A. Implementation of Alternative B would have more impacts on soils, vegetation, desert tortoise, and other wildlife than Alternative A (Table 3). Under Alternative C, the dam and detention basin would be located above the Tuacahn Amphitheatre rather than on the property purchased by the City with the intention of building a detention dam. Under Alternative C, no surface disturbance would occur within designated critical habitat for the desert tortoise, although inundation may occur there during floods. Access to the site would be via an existing dirt road and the amount of disturbance associated with the dam and inundated area would be noticeably less than under Alternative A (Table 1). Implementation of Alternative C would have less impact on soils, vegetation, wildlife, recreation, and desert tortoises than under Alternative A. However, under Alternative C, the basin would only have a capacity of 22 acre-feet as apposed to 44 acre-feet under Alternative A. Alternative C thus only partially addresses the flooding and subsequent damage to property during a 25-year flood. Overall, Alternative C would provide a moderate benefit in terms of preventing flood damage, while Alterna...
