Characterization of Alluvial Fan Reach of Copeland Creek Russo, I., Anfinson, O., Goman, M., Robinson, H. Dooley, T., Hole, C., Hutchinson, S. Department of Geology, Sonoma State University, Rohnert Park, CA

Abstract Alluvial Fan Reach of Copeland Creek Study Reach Copeland Creek is a small perennial which runs through the northern Survey Transects Study Reach margin of the SSU campus. Where it emerges from and enters Copeland Creek XS1 Copeland Creek Streets the valley floor, it forms an alluvial fan as the creek slows down and deposits its bed r

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l y load. During the winter of 2016-2017, a series of heavy storms caused a section i XS2

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of Copeland Creek adjacent to Lichau Road to overflow its banks, causing major m y

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damage to the roadway. This flooding event threatened to change the course of t s

e re Copeland Creek and jump watersheds to the Petaluma River, in a process known XS3 as avulsion. C Fig. 6 Map of study reach of Copeland Creek. This study aims to characterize the apex region of the alluvial fan, which poses the highest risk of avulsion in future flood events. A longitudinal profile and three channel cross sections were measured using auto-level and stadia-rod. Using a Copeland Creek Survey Data GIS, sinuosity was determined to be 1.2 and channel slope for the entire alluvial fan Cotati 46 reach was calculated as 0.022. The channel slope of the study reach was measured as 0.032. Using a Wolman pebble count, the D50 grain size of the bed material was ich 460 au measured at ~60 mm (very coarse gravel.) We categorized this reach of Copeland Creek as a C4b using the Rogen Classification scheme. 4 ) t f

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R Transects Future SCW etention asin 44 lluvial Fan of Copeland Creek Russian River Watershed Copeland Creek Sonoma State University

etaluma River Watershed × Study Reach vulsion Site 440 0 1.7 3. 7 10. 14 otential vulsion Channel Russian River Watershed × ilometers etaluma River Watershed Streets 43 0 0 100 10 200 20 300 30 400 0 0.3 0.6 1.2 1. 2.4 istance (ft)

ilometers Thalweg Water Surface ankfull verage ankfull verage Water Surface

Fig. 2 Map of alluvial fan reach of Copeland Creek, displaying concentric topographic circles characteristic of alluvial fans. Potential avulsion Fig. 7 Plot of surveyed longitudinal profile of Copeland Creek study reach. Note the average bankfull and average channel, shown in red, drains into the Petaluma River watershed, where the current channel drains into the Laguna de Santa Rosa, part of the water surface lines converging in the downsteam direction. larger Russian River watershed. Study reach (pink) is area of figure 6.

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LIDAR Transects Wolman Pebble Count 462 n ) t o f i ( t 46

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n 44 e 0 Copeland Creek. Not the secondary channel and the 420 ft 447 m i

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26 ft Fig. 4 Cumulative size distribution of bedding particles in Copeland Creek main channel, just below aluvial fan apex. D50 ~= 16 mm Conclusion 263 ft Fig. 1 Location map of study area. Red inset is area of figure 2 • Established baseline measurements for longitudinal profile and cross sections. 27 ft • Future classes may use our baseline measurements to determine long-term changes in channel morphology. Methods 21 ft • Convergence of bankfull and water level shows increased chance of avulsion in down- Sources Esri ERE eorme ntermap increment Corp. EC USS stream direction. F S RC eoase adaster rdnance Survey Esri apan MET Esri China (ong ong) swisstopo Mapmyndia penStreetMap 24 ft The longitudinal profile was mesuredc onusingtriutors anad thLeicae S Us er CNA532ommunity autolevel and 16 ft 0 ft 00 ft 1000 ft 100 ft 2000 ft 200 ft 3000 ft • LIDAR data shows that some portions of the avulsion channel lie at a lower elevation stadia rod, using the protocol developed by Wildland . A 150 ft tape was than the channel of Copeland Creek. 21 ft laid along the stream centerline and the stream thalweg, watersurface and bankfull c. were measured every 5 to 10 feet, taking care to capture riffles, runs and pools. This process was repeated until we had captured a reach of 422 ft - slightly more

than 20 bankfull widths. 20 ft Three cross sectional stream profiles were measured again using a Leica NA532 autolevel and 16 ft stadia rod and the autolevel’s rangefinding capabilities. Ackowledgements Bed composition was determed using the Wolman Pebble Count method. 1 ft Transects in our study reach were chosen at random and a step-toe approach was 0 ft 1000 ft 2000 ft 3000 ft 4000 ft 000 ft We would like to thank John Monaghan, Susan Haydon, and Michael Thompson from

used to select samples across the transect. A Gravelometer or 150 ft tape was used Main channel elevation Main channel Avulsion channel the Sonoma County Water Agency for their assistance with background information and parcel data. We would also like to extend our thanks to The WATER Collaborative and to measure the b axis of samples. Fig 3. Cross sectional profiles of Copeland Creek’s alluvial fan Fig 5. Aerial image of partial avulsion on Lichau Road near Cold Springs Maps and LIDAR Transects were generated using ArcGIS 10.5 and Adobe Illus- derived from LIDAR data. a) A-A′; vertical exageration ~ 5:1 b) Road. 01/20/2017 the Center for Undergraduate Research and Creative Experiences for the funding which trator, using data from the Sonoma County Vegetation Mapping & LIDAR program. B-B′; vertical exageration ~64:1 c) C-C′; vertical exageration allowed us to complete this study. ~12:1