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1 I I I I I I I I I :1 I I I I I I I I I 1.0 INTRODUCTION 1.1 Background The Upper Colorado River Endangered Fish Recovery Program (Recovery Program) has invested considerable time and resources on identification, acquisition, and restoration of riverine floodplains as nursery habitat for the endangered razorback sucker (Xyrauchen texanus; e.g., FLO Engineering 1997; Nelson and Soker 2002). River floodplains are believed to be important nursery and rearing habitats for the species (Tyus and Karp 1990; Modde 1996, 1997; Muth et al. 1998; Wydoski and Wick 1998). A major element of the Recovery Program is Habitat Development, with the goal "to improve and maintain sufficient habitat to support the endangered fish species; and to apply habitat development and enhancement techniques experimentally to determine if the rare fishes will use developed habitat and if such techniques contribute to recovery." As of November, 2002, a total of 1,087.2 acres have been acquired by the Recovery Program for a total cost of$2,117,400. The Recovery Program is interested in knowing if sufficient floodplain habitats are available to recover the endangered razorback sucker and to support recovered populations. The amount of floodplain habitat available on any given year is dependent on river stage. A reconnaissance inventory ofbottomlands (Irving and Burdick 1995) identified 132 bottomland habitat sites with a potential of 18,430 acres along 393 miles of the Green River in 1993. Of this total, 7,720 acres (74 sites) were inundated during the May high-water flow period (18,200 cfs) and 2,438 acres (28 sites) in the September low-water flow period (1,560 cfs). The largest flooded bottomland areas were located in the Browns Park National Wildlife Refuge reach (RM 368-393; 1,371 acres inundated in May) and between Pariette Draw and Escalante Ranch (RM 238-310; 6,093 acres inun~ted in May). A follow-up effort by Irving and Day (1996) revealed 48,485 potential acres ofbottomlands in 111 inve~toried sites; only 6,113 acres were flooded in May 1993, and 11,254 acres could be flooded with historic floods. Bell et al. (1998) analyzed photographs and quantified surface area of inundation as a function of flow at the Jensen gage. Inundated bottomland area between Split Mountain ,(RM 319) and Pariette Wash (RM 240) was 5,904 acres at 20,000 cfs; 9,550 acres at 22,000 cfs; and 13,927 acres at 25,000 cfs. Average peak flow of the Green River near Jensen for 56 years of record through 2000, is 19,706 cfs.