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Existing Channel Modification Alternative - The river cross section geometry would be reconstructed within the present channel alignment to create a functional step-pool or rapid-pool system. Existing river levees would be retained where possible, or relocated outward from their present positions. The design improves channel habitat and vertical stabilily, and continues to convey design flood flows within existing flood or dike easements. The construction of the new channel geometry and associated conveyance features could require the removal of a majority of the existing vegetation in many of the reaches. However. woody vegetation such as trees and willows would be preserved wherever possible in order to maintain stability of the existing dike and overbank/floodplain system and to reduce the short-term loss of valuable riparian habitat. Riverine Habitat Restoration Alternative - A majority of the existing channeUfloodplain system would be reconstructed in a meandering riffle-pool alignment to recreate a naturally functioning river system in dynamic equilibrium with the current valley and hydrologic characteristics. Existing dikes would be removed in almost all locations to re-establish contact between the channel and the floodplain. The sinuous channel planform provides opportunities for incorporation of existing channel vegetation as well as remnants of pre-diking vegetation and channel features which were abandoned when the Provo River was channelized over 40 years ago. Ponds and small side channels would be constructed in the floodplain to provide additional diversity and habitat features. The ECMA and the RHRA would both make major changes to the existing channel in order to develop a self- sustaining, functional river system. The primary difference is that the ECMA would work almost entirely within the present leveed area or present channel alignment, whereas the RHRA would not be constrained to the present alignment. Figure 2 shows schematic diagrams of typical river cross sections under these two alternatives. HYDROLOGY All of the alternatives were designed with the same assumed hydrology, based on proposed water releases from Jordanelle Dam. Design hydrology is summarized in Table 1. The 1.5-year peak discharge was adopted as the bankfull discharge for channel design. Table 1 Summary of Design Hydrology Pre-Jordanelle Dam Post-Jordanelle Dam Conditions Hvdrolo2ic Parameter Conditions (PRRP Desi2n Hvdrolo2v) Base Flow Ocfs 125 cfs Mean Annual Dischar2e 260 cfs 260 cfs 1.5- Y ear Peak Dischar.e 2,100 cfs 1.200 cfs 5- Y ear Dischar2e 3,140 cfs 1.900 cfs 10- Y ear Dischar2e 3,610 cfs 2,180 cfs 50-Year Dischar2e 4,580 cfs 2,680 cfs 100- Year Dischar2e 4,980 cfs 2.860 cfs GEOMORPHOLOGY Geomorphic investigations of the Provo River and related river systems were conducted for the PRRP. The plhl'ose of these investigations was to provide an understanding of the pre-disturbance morphology (channel pattern, hydrau!';c geometry and dynamic adjustments in planform) and to develop stable channel design parameters for restoration of the river and riparian system. The development of such parameters reflects an understanding of the entire fluvial system and the variables which impact the behavior of the system. Such variables include: (a) geology and the geologic development of the valley and channel; (b) parent material and sediment sources; (c) transfer of sediment through the system; (d) adjustments in hydrologic and hydraulic conditions through natural and man-induced processes; (e) adjustments in base level (reservoir control); (f) changes in land use and vegetation; and (g) the response of the channel to diking. Geomorphic design criteria were developed using classical empirical relationships (e.g., Williams (1986), Leopck': and Maddock (1953)), template stream analysis, and stream type classification relationships (e.g., Rosgen (1993)). The geomorphic design crileria for each feasibility-level design alternative are presented in Table 2. 3