VOOI^ ^'bOU^'^ ^[^tV Utah State University Contract93-1070. amendments 3 and 6 (Flaming Gorge Studies: Reproduction and recruitment of Gila spp. and Colorado squawfish in the middle Green River) A GEOMORPHIC ASSESSMENT OF THE AVAILABILITY OF POTENTIAL HUMPBACK CHUB HABITAT IN THE GREEN RIVER IN DESOLATION AND GRAY CANYONS, UTAH DRAFT FINAL REPORT K. Lynn Orchard Watershed Science Unit and John C. Schmidt DepartmentofGeography and Earth Resources Utah State University Logan, Utah 84322-5240 March 1998 Utah State University Contract 93-1070. amendments 3 and 6 (Flaming Gorge Studies: Reproduction and recruitment of Gila spp. and Colorado m squawfish the middle Green River) A GEOMORPHIC ASSESSMENT OF THE AVAILABILITY OF POTENTIAL HUMPBACK CHUB HABITAT IN THE GREEN RIVER IN DESOLATION AND GRAY CANYONS, UTAH DRAFT FINAL REPORT K. Lynn Orchard Watershed Science Umt and John C. Schmidt DepartmentofGeography and Earth Resources Utah State University Logan, Utah 84322-5240 March 1998 ABSTRACT The size and number oflow-velocity eddies that may be preferred habitat for the endangered humpback chub (Gila cypha) in the Green River in Desolation and Gray Canyons changes with discharge and has changed since the early 1900's. We determined the present extent and distribution ofthese habitats by mapping low-velocity eddies at a scale of 1:5000 at 5 or 6 discharges between 2,100 and 27,000 ftVs in four 8-km reaches that are regularly sampled by the Utah Division ofWildlife Resources. We also mapped the surficial geology ofthese study reaches and the distribution of bed substrate that are emergent at 2000 ftVs. We analyzed the distribution ofthese areas within a geographic information system. The availability ofhabitat prior to completion ofFlaming Gorge Dam was estimated by matching old obhque photographs, analyzing old aerial photos, and recomputing habitat availability prior to channel change. The total area oflow-velocity eddies, when summed for the 4 study reaches, does not change with discharge, but the relative distribution ofthese eddies among the 4 study reaches does change. Also, the type ofeddies changes with discharge. At low discharge, the greatest proportion ofthe total area oflow-velocity eddies occurs as small shoreline eddies, but the greatest proportion occurs in a few large eddies at higherdischarges. At low discharge, the river bank is highly contorted and is dominandy bare sand and gravel. At high discharge, the river bank has a simpler shape, and much ofthe shoreline is inundated vegetation. The Green River channel is 19% narrower today than it was in the 1920's, and riparian vegetation has estabUshed itselfat low elevations and on formerly active mid- We channel islands. estimate that the substrate ofmost nearshore habitats was sand or gravel prior to channel narrowing. For purposes ofdeveloping flow recommendations, our results must be integrated with the results ofecological studies which identify the relative importance of the different habitats in the life history of the target species. Digitized by the Internet Archive in 2012 with funding from LYRASIS IVIembers and Sloan Foundation http://archive.org/details/geomorphicassessOOorch TABLE OF CONTENTS ABSTRACT H LIST OF TABLES IV LISTOFRGURES V INTRODUCTION 1 STUDY AREA 3 METHODS 8 FieldMapping-SurhcialGeology 9 FieldMapping-FlowPatternsAndNear-Shore Substrate 11 GPS 12 GIS DatabaseCreation 13 ChannelCross-Sections 13 PhotoMatching 15 .^ RESULTS 19 CharacteristicsoftheAlluvialValley- SurhcialMapping 19 ChannelGeometry 26 EvidenceofChannelNarrowing- HistoricPhotoMatching 28 EstimationofDegreeofChannelNarrowing 42 ModernDistributionofHabitats 42 Effectofdischargeonsizeanddistributionofeddies 49 DistributionofShorelineHabitats 49 ConceptualModeloftheDistributionofShorelineHabitatsPriortoChannel Narrowing 56 DISCUSSION 61 ACKNOWLEDGMENTS 62 LITERATURE CITED 63 APPENDICES 64 A. SUMMARY OF SoTOGRAPHIC iNF6RMATi6N.'lV.................64 B. DESCRIPTION OF MAP UNITS 65 PLATES SURFICIAL GEOLOGY OF 4 REPRESENTATIVE REACHES OF THE GREEN RIVER IN DESOLATION AND GRAY CANYONS 69 ui .. . LIST OF TABLES Table Page SUMMARY OF REACH CHARACTERISTICS WHICH ARE 1 INFLUENCED BY THE PREDOMINANT BEDROCK GEOLOGY 6 SUMMARY OF AIR PHOTO INFORMATION 2. 18 3 DISTRIBUTION OF SURFICIAL DEPOSITS IN THE ALLUVIAL VALLEYS OF THE 4 STUDY REACHES 20 BANK MATERIAL INUNDATED AT THE SHORELINE DURING 4. BANKFULL DISCHARGE 27 5 SUMMARY OFWIDTH/DEPTH RATIOS AND BED-MATERIAL . AT MEASURED CROSS-SECTIONS 27 6. DISCHARGES OF SPECIFIC RETURN PERIOD FOR THREE TIME INTERVALS 41 7 AREA OCCUPIED BY THE ACTIVE CHANNEL, FLOODPLAIN, . AND COTTONWOOD TERRACE 43 8 PERCENTAGE OF THE HISTORIC CHANNEL NOW OCCUPIED . BY THE MODERN FLOODPLAINAND COTTONWOOD TERRACE 43 9. ESTIMATIONS OF NARROWING OF THE GREEN RIVER'S CHANNEL 44 ANALYSIS OF VARL\NCE COMPARING AREA OF LOW-VELOCITY 10. HABITATS BY REACH AND DISCHARGE 46 ANALYSIS OF VARIANCE COMPARING MEAN EDDY SIZE 1 1 AT DIFFERENT DISCHARGES 47 PERCENTAGE OFTHE TOTAL SHORELINE LOCATED WITHIN 12. EDDIES AT A WIDE RANGE OF DISCHARGES 58 IV