Field Trip Report Susitna-Watana Ice Processes Study December 3

December 3, 2012 Field Trip Report

Susitna-Watana Ice Processes Study

Date : December 3, 2012

Crew : Robin Beebee Ingrid Corson (HDR Alaska); pilot Alicen Bishop (JayHawk Aviation)

Talkeetna Weather : Sunny, temperatures varied from 0 to 17 degrees Fahrenheit (F), light winds.

Objectives : Aerial survey of ice on Susitna River, Mouth to Oshetna Confluence.

Data Collected:



Photos (JPEG)



GPS points (ArcGIS Geodatabase) with notes



Contour Video

Summary : Continued cold, clear weather without snow accumulation. On the lower river windblown sediment from exposed gravel bars had begun to accumulate on the bare ice surface. Open leads showed signs of encroaching ice, both from the sides as well as frazil accumulation along the bottom. Open leads in the main channel had visible frazil flowing in them, indicating they were velocity rather than thermal leads. Sunshine Slough and some side channels had black thermal ice forming on them.

Ice cover on the Middle River had progressed to PRM 142, up from PRM 134 during the

November 28, 2012 survey, and was continuing to accumulate with frazil buildup and border ice narrowing the channel. There was still a break in ice cover at PRM 122. Overflow at the upstream end of ice cover had lessened compared to previous flights. Middle river sloughs were frozen with no thermal leads. Ice bridges in Devil Canyon remained similar to the November 28,

2012 survey; there was heavy frazil in this reach. Ice bridges upstream of the canyon had expanded and two new ones had formed. At the Dam Site there were signs that ice cover had broken out and reformed.

On the Upper River, new ice cover had formed upstream of a bridge at PRM 189. The upper end of ice cover had progressed only a half mile since November 28, 2012 and appeared to be growing in border ice at the banks around a long, narrow open lead. The Oshetna River remained open.

Flight Path : The team departed Merrill Field and landed at the Susitna River’s mouth to set up and mount the video camera. Camera mount failed a few minutes after take-off; landed again at transmission line to restart. The team then flew the far west side channel/Alexander Slough to

Susitna Station, then the eastern side channel past Deshka Landing through the Delta Islands.

They refueled in Talkeetna, and then flew nonstop to the Oshetna River confluence. They returned along Stephan Lake, Talkeetna River, refueled in Talkeetna, then flew back to

Anchorage, returning at sunset.

Susitna-Watana Hydroelectric Project

FERC Project No. 14241 Page 1

Alaska Energy Authority

Draft: August 8, 2013

F IELD T RIP R EPORT S USITNA -W ATANA I CE P ROCESSES S TUDY

Lower River Observations

Air temperatures in the Lower River varied from 10 to 19 degrees F. The ice cover appeared stable with very little snow cover. Wind-blown sediment from bare gravel bars was accumulating

on top of the ice (Figure 1). The hummocky topography on the ice cover was still visible due to

lack of snow, and it was easy to differentiate between smooth overflow ice, broken covers, and thickened covers. Most open leads were showing signs of encroachment by border ice from the

sides and/or light frazil accumulation from the bottom (Figure 2). Main channel open leads had

visible frazil flowing in them, indicating that the water in the leads was slightly super-cooled and the leads were likely velocity leads rather than thermal in origin. In places, especially near

Talkeetna, anchor ice was building up and creating small rapids in main channel leads. Many

side sloughs were freezing over with black thermal ice, including Sunshine Slough (Figure 3).

Almost all of the Lower River main channel braids were covered with hummocky frozen slush ice, while some side channels and gravel bars were covered with smooth thermal ice.

Talkeetna and Chulitna Rivers: Open leads persisted in the Talkeetna and Chulitna Rivers and in

the main Susitna River near the confluence (Figure 4, Figure 5). The Chulitna River had frozen over and smooth overflow ice formed over many of the gravel bars (Figure 6).

Middle River Observations

Air temperatures in the Middle River varied from 4 to 15 degrees F.

Middle River Sloughs: Whiskers Slough (Figure 7), Slough 6A (Figure 8), and Slough 8A were

ice-covered without evidence of thermal leads. Slough 9 had a small open lead at the mouth, and

Slough 11 had a substantial open lead at the mouth, but little flow upstream of the mouth. Slough

21 was ice covered.

Chulitna River to Gold Creek Bridge: The main channel ice cover varies from hummocky frozen slush ice (“jammed” ice) from Talkeetna to Curry, to stretches of smooth overflow and thermal

ice alternating with hummocky ice upstream of Curry (Figure 9). Open leads in the ice-covered

main channel were frequent and carrying frazil, and anchor ice was still accumulating in riffles.

Upstream of the leading edge of the ice cover, frazil was heavy and occupied much of the

channel width; border ice was narrowing the main channel (Figure 10).

Gold Creek Bridge to Portage Creek: Ice cover had progressed past Gold Creek Bridge to PRM

142 (Figure 11), which was freezing over by border ice growth. The upstream end of the ice cover was just upstream of the Indian River confluence (Figure 12) and was progressing still by

frazil accumulation. Less flooding around the upstream end of the ice cover was evident compared to past flights.

Portage Creek to Devil Creek: Portage Creek was ice covered. Bridging in Devil Canyon was similar to last week (November 28, 2012), except the bridge just upstream from Portage Creek had increased slightly in size. Heavy frazil was evident throughout Devil Canyon, and appeared to compress into pans in open, calm reaches and break into slush in anchor-ice rapids and when

passing under ice bridges (Figure 13).

Devil Creek to Dam Site: Upstream of Devil Canyon, frazil was much lighter. Two new ice bridges covered the channel between PRM 172.1 and PRM 173, and PRM 183.1 to PRM 183.6.






The bridge at PRM 176 had grown larger from the downstream end (Figure 14). Ice cover at the

Dam Site appears to have broken out and then reformed – there was a channel in the middle of

the hummocky ice cover that was filled with differently-textured hummocky ice (Figure 15). Fog

Creek, and Tsusena Creek were all ice covered.

Upper River Observations

Air temperatures in the Upper River varied from -5 to -15 degrees F. Since the previous survey on November 28, 2012, new ice cover had started progressing upstream from a bridge near PRM

189. The cover appeared to have jammed and broken out, leaving sizable open leads between

thick accumulations of hummocky ice (Figure 16). There was a break in cover from PRM 193 to

PRM 194. The ice cover then extended upstream to just downstream from Vee canyon at PRM

223. Within the ice cover, open leads appeared to be narrowing and most carried frazil. The upstream end of the ice cover was not a river-wide front of accumulating frazil, but a gradually

widening open lead (Figure 17). The ice cover had advanced only about a half mile since

November 28, 2013. Floating ice chunks upstream from Vee canyon appeared to have come

from broken shore ice constrictions near the Oshetna River confluence (Figure 18).

Watana Creek, Kosina Creek, and Goose Creek were ice covered at the mouth. Kosina Creek had

hummocky dirty ice jam deposits around the mouth of the creek (Figure 19). Oshetna River had

continuous open water at the mouth despite the cold temperatures (Figure 20, Figure 21).

Returning to Talkeetna, the team noted an unusual accumulation of very rounded ice chunks in a

small rapid in the Talkeetna River canyon (Figure 22).





F IELD T RIP R EPORT

Representative Photographs

S USITNA -W ATANA I CE P ROCESSES S TUDY

Figure 1. Windblown sediment from gravel bars on top of hummocky ice cover.

Frozen Alexander Creek can be seen in middle left, PRM24.

Figure 2. Looking upstream. Velocity lead in main channel filling in from bottom with frazil ice, PRM 78.






Figure 3. Looking upstream toward Sunshine Slough. Black ice forming over open leads in Sunshine Slough, PRM 88.

Figure 4. Mouth of the Talkeetna River, looking downstream to the Susitna River, PRM 101






Figure 5. Looking up the Chulitna River from the Susitna River, PRM 102.

Figure 6. Open lead in main channel of the Susitna River, PRM 101.






Figure 7. Looking upstream from to mouth of Whisker Slough, PRM 105.

Figure 8. Looking upstream at the mouth of Slough 6A.






Figure 9. Smooth ice forming between ice bridge at Curry Station, PRM 123.

Figure 10. Heavy frazil ice flowing into anchor ice rapids, flow from top to bottom of photo, PRM 149.






Figure 11. Short open reach in Middle River, PRM 122.

Figure 12. Upstream end of ice cover in Middle River. Flow from right to left.

Note bare gravel bar, indicating low water level, PRM 142.






Figure 13. Frazil ice in Devil Canyon. Flow from right to left. Compressed frazil pans were flowing into anchor ice rapids and breaking up into smaller slush pieces, PRM 157.

Figure 14. Ice bridge. Fresh ice cover has accumulated on the bottom end of the cover, perhaps because of backwater upstream of the anchor ice deposit in the lower left of the picture. Flow from top to bottom. PRM 176.






Figure 15. Complex ice cover at dam site. Flow from top of bottom. PRM 187.

Figure 16. Open leads in anchor ice and complex ice cover. Flow from top to bottom. PRM 189.






Figure 17. Upstream end of ice cover, PRM 225.

Figure 18. Broken ice flowing down Upper River, PRM 230.






Figure 19. Mouth of Kosina Creek, flow from top to bottom, PRM 209.

Figure 20. Oshetna River confluence, flow from top to bottom. PRM 235.






Figure 21. Open water on the Oshetna River. Dark portions of bank next to river were flooded during

November 15 breakout flood. PRM 234.

Figure 22. Ice spheres behind anchor ice dam on Talkeetna River.





Field Trip Report Susitna-Watana Ice Processes Study December 3

December 3, 2012 Field Trip Report

Susitna-Watana Ice Processes Study

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Field Trip Report Susitna-Watana Ice Processes Study December 3

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