I ••1 . I SUSITNA HYDROELECTRIC PROJECT . -. .. ::· ": • •J .·! I . i I MIDDLE SUSITNA RIVER SEDIMENTATION STUDY STREAM CHANNEL STABILITY ANALYSIS I OF SELECTED SLOUGHS, SIDE CHANNELS AND MAIN CHANNEL LOCATIONS I I I Report by I Harza-Ebasco Susitna Joint Venture I Prepared for Alaska Power Authority I I I I I March 1985 I I I I I I 'l'A.BLE OF CORTENTS I SECTION/TITLE PAGE List of Tables ;li I List of Exhibits ;., 1.0 SUMMARY I 3 2.0 BACKGROUND I .1 3.0 SCOPE OF STUDY 4.0 SETTING s I 7 5.0 STUDY SITES , 5.1 Main Channel Near River Cross Section 4 I 5.2 Main Channel Between River Cross Sections • 12 and 13 , 5.3 Main Channel Upstream From Lane Creek I ,... 5.4 Mainste!m 2 Side Channel at River Cross 8 I Section 18.2 5.5 Slough 8A 5.6 Slough 9 ' I 5.7 Main Channel Upstream Fr~ 4th of July Creek ' 5.8 Side Channel 10 ' I 5.9 Lower Side Channel 11 ' 5.10 Slough 11 ,. I 5.11 Upper Side Channel 11 5.12 Main Channel Between River Cross Sections ,. I 46 and 48 ,. 5.13 Side Channel 21 ,, I 5.14 Slough 21 6.0 DATA SOURCES " I I I -i- I I I I TABLE OF CONTENTS I SECTION/TITLE 7.0 GENERAL APPROACH I 7.1 Degradation 7.1.1 Competent Bottom Velocity ,, I 7.1.2 Tractive Force 7.1.3 Meyer-Peter, Muller Formula 1.1 7.1.4 Schoklitsch Formula I 7.1.5 Shields Criteria II 7.1.6 Depth of Degradation I 7.2 Aggradation 8.0 HYDRAULIC DATA USED IN THE ANALYSIS I 8.1 Dominant Discharge 8.2 Mean Velocities, Average Depths and I Channel Widths 8.3 Channel Bed Slopes 8.4 Hanning's Roughness Coefficients I 8.5 Bed Material Size Distribution 9.0 SEDIMENTATION PROCESS I 9.1 Natural Conditions ,, 9.1.1. River Morphology I 9.1.2. Channel Stability 9.1.3. Intrusion of Fine Sediments I 9.2 With-Project Conditions 9 . 2.1 River Morphology 9.2.2 Channel Stability Jl I 9.2.3 Intrusion of Fine Sediments u ~tr~£tte/llt't.s - TABLES I EXHIBITS I APPENDIX A I -11- I I I I LIST OF TABLES I Nuober Title 1 Characteristics of Study Sites on Middle Susitna I River 2 Hydraulic Parameters for Mainstem Sites I 3 Hydraulic Parameters for Side Channels and Sloughs I 4 Representative Bed Material Size Distribution for Selected Sloughs, Side Channels and Main­ stem Sites I 5 Transportable Bed Material Sizes in Selected Sloughs, Side Channels and Mainstem Sites I 6 Potential Degradation in Selected Sloughs, Side Channels and Mainstem Sites I 7 Natural and With-Project Average Weekly Flows of Susitna River at Gold Creek 8 Maxhnuil Natural and With-Project Weekly Flows I of Susitna Riv~r at Gold Creek I I I I I I I I -iii- I I I LIST OF EXHIBITS I Number Title I 1 Location Map 2 Locations of Study Sites 3 Main Channel near River Cross Section 4 I 4 Main Channel between River Cross Sections 12 and 13 5 Main Channel upstream from Lane Creek I 6 Hainstem 2 Side Channel 7 Slough SA I 8 Slough 9 9 Main Channel upstream from 4th of July Creek I 10 Side Channel 10 11 Lower Side Channel 11 12 Slough 11 I 13 Upper Side Channel 11 14 Main Channel between River Cross Sections 46 I and 48 15 Side Channel 21 I 16 Slough 21 17 Relatiouship between Particle Size and Bottom I Velocity 18 Relationship between Mean Diameter and Critical Tractive Force I 19 Relations hips between Slough/Side Channel l)ischarge and Discharge at Gold Creek I 20 Hydraulic Parameters for Slough 9 21 Hydraulic Parameters for Lower Channel 11 I 22 Size Distribution of Bed Material in Main Channel near Cross Section 4 I 23 Size Distribution of Bed Material in Main Channel between Cross Sections 12 and 13 24 Size Distribution of Bed Material in Main Channel upstream I from Lane Creek I -iv- I I I LIST OF EXHIBITS I Number Title 25 Size Distribution of Bed Material in Mainsteam & I Side Channels at Cross Section 18.2 26 Size Distribution of Bed Material in Slough SA I 27 Size Distribution of Bed Material in Slough 9 2S Size Distribution of Bed Material in Main I Channel upstream from 4th of July Creek 29 Size Distribution of Bed Material in Side Channel 10 I 30 Size Distribution of Bed Material in Lower Side Channel 11 I 31 Size Distribution of Bed Material in Slough 11 and Upper Side Channel 11 I 32 Size Distribution of Bed Material in Main Channel between Cross Sections 46 and 4S I 33 Size Distribution of Bed Material in Side Channel 21 and Slough 21 34 Transportable Bed Material Sizes in Hain I Channel near Cross Section 4 35 Transportable Bed Material Sizes in Main I Channel between Cross Sections 12 and 13 36 Transportable Bed Material Sizes in Main I Channel upstream from Lane Creek 37 Transportable Bed Uaterial Sizes in Mainstem 2 I Side Channel 3S Transportable Bed l-faterial Sizes in Slough SA 39 Transportable Bed Material Sizes in Slough 9 I 40 Transportable Bed Material Sizes in Main Channel upstream from 4th of July Creek I 41 Transportable Bed Material Sizes in Side Channel 10 I 42 Transportable Bed Material Sizes in Lower Side Channel 11 I -v- I I I LIST OF EXHIBITS I Number Title 43· Transportable Bed Material Sizes in Slough 11 I 44 Transportable Bed Material Sizes in Upper Side Channel 11 I 45 Transportable Bed Material Sizes in Main Channel between Cross Sections 46 and 48 46 Transportable Bed Material Sizes in Side I Channel 21 47 Transportable Bed Material Sizes in Slough 21 I 48 Estimated Depth of Degradation in Main Channel near Cross Section 4 I 49 Estimated Depth of Degradation in Main Channel between Cross Sections 12 and 13 I 50 Estimated Depth of Degradation in Main Channel upstream from Lane Creek 51 Estimated Depth of Degradation in Mainstem 2 Side Channel 52 Estimated Depth of Degradation in Slough 9 I 53 Esti~ted Depth of Degradation in Main Channel upstream from 4th of July Creek I 54 Estimated Depth of Degradation in Side Channel 10 I 55 Estimated Depth of Degradation in Lower Side Channel 11 56 Estimated Depth of Degradation in Upper Side I Channel 11 57 Estimated Depth of Degradation in Main Channel I between Cross Sections 46 and 48 sa Estimated Depth of Degradation in Side Channel I 21 59 Estimated Depth of Degradation in Slough 21 I I -vi- I I I I 1.0 SUMMARY I This study was conducted to evaluate potential effects of the Susitna Hydro­ electric Project on channel stability at selected sites in the mainstem and I at selected sloughs and side channels. The sediment at ion process in the Susitna River under natural conditions also is discussed. The study reach I includes the Susitna River between Devil Canyon and the confluence of the Susitna and Chulitna rivers. The selected sites (shown on Exhibit 2) are : I 1. Mainstem Sites: near river Cross Section 4, river miles 99.0 to 100.0; between river cross sections 12 and 13, river miles 108.5 I to 110.0; upst ream from Lane Creek, river miles 113.6 to 114.2; upstream from 4th of July Creek, river miles 131.2 to 132.2 and I between river cross sections 46 and 48, river miles 136.9 to 137.4. I 2. Side Channels: Mainstem 2 Side Channel, Side Channel 10, Lower I and Upper Side Channels 11 and Side Channel 21. 3. Sloughs: SA, 9, 11 and 21. I For natural conditions, temporal deposition and/or scour was studied at the I sites in qualitative terms. Under with-project conditions, a more quantitative estimate of potential degradation and/or aggradation was made I for each study site. Intrusion of fine sediment into the gravel bed and its subsequent entrapment also were studied. I The hydraulic and sediment data required for the study were derived from various reports prepared by the Alaska Department of Fish ani Game, Susitna I Hydro Aquatic Studies Team; R&M Consultants, Incorporated; U.S. Geological Survey, Water Resources Division, Anchora·ge; and Harza-Ebasco Susitna Joint I Venture during 1983 and 1984. The data were used to develop relationships I I 42188202 1 850404 I I between the discharge rates at Gold Creek stream gaging station and corresponding flows at the mainstem sites and the flows entering the sloughs I and side channels. These data also were used to estimate mean velocities, coverage depths and channel widths at each site. The bed material size I distribution representative for the material at each site was derived from the analysis of the bed material samples collected by Harza-Ebasco. I The sizes of transportable bed material corresponding to a selected range of discharges were estimated as the average of the five sizes computed using I the methods of competent bottom velocity; tractive force; Meyer-Peter, Muller formula; Schoklitscb formula and Shields criteria. A comparison of I median bed material size and the transportable size at each site indicated that under natural conditions, most of the selected sites are subject to I temporal scour and/or deposition depending upon the magnitude and characteristics of the sediment load and high flows caused by floods or I breaching of ice jams.