Modeling Storm-Induced Inundation on the Yukon Kuskokwim Delta for Present and Future Climates

Tom Ravens and Jon Allen, Univ. of Alaska Anchorage

10 km 10 km

Kashunuk R.

Research Goal: determine the likely change in YK Delta ecology due to storm surges – enhanced by sea level rise

• Tasks:– Develop and validate a storm surge model– Identify a number of representative storms from the past 40 years– Model these storms and their inundation under present climate conditions– Re-model these storms assuming one or more sea level rise scenarios– Compute an inundation index from each model run– Compute an annual inundation index based on inundation indices from

selected storms – Establish the relationship between annual index and ecological parameters

(e.g., vegetation type) under present climate– Infer changes in ecological parameters (e.g., vegetation type) under a

future climate based on projected changes in inundation index

Storm surge modeling -course grid model domain

YK Delta

Storm surge modeling –fine scale model of YK Delta

Kashunuk RiverHooper Bay

Measured and Modeled storm surge at coast on YK Delta

11/9/2009 11/10/2009 11/11/2009 11/12/2009 11/13/2009 11/14/2009-1

-0.5

0

0.5

1

1.5

2

2.5

3

measurement

model

date (local time)

wat

er le

vel (

m, m

sl)

Storms to studyStorm Date

Max surge1 (ft MLLW Hooper Bay)

Return period1 (yr)

Min Surface Pressure1

(mb)

Max wind1 (mph direction)

Max surge Kashunuk2 (Ft, MLLW)

Estimated return period (yr, Kashunuk River

1 Nov 74 13.57 50 978.6 45.6 SSW

2 Oct 92 11.70 10–15 981.6 51.2 SSE

3 Oct 95 11.60 10 998.3 49.7 SE

4 Oct 96 10.78 5–10 1008.4 39.6 S

5 Nov 96 11.60 10 975.0 49.7 SE

6 Oct 04 11.83 15 975.7 43.4 SW 9.6 5

7 Sept 05 11.9 15

8 Nov 06

9 Nov 09 7.6 1

10

Nov 11

1Chapman et al. Storm-Induced Water Level Prediction Study for the Western Coast of Alaska, USACE. Reported surge is for Hooper Bay. It does not include tides. 2 Calculated using ADCIRC (course grid) and DELFT3D (fine grid) models. Reported surge is for lower Kashunuk River. It does not include tides.

1 year, 2.5 m15 year, 4 m

5 year, 3.2 m

AK time

GMT

1 year storm inundation indexwide view close-up

[m-days]

[m-days]

5 year storm inundation indexwide view close-up

[m-days]

[m-days]

15 year storm inundation indexwide view close-up

[m-days]

[m-days]

Annual Inundation Index for current climate based on a weighted averageof indices from the 1, 5, and 15 year storm (using weights of 1, 1/5, 1/15 - approximately)

Nearshore InundationIndex dominated by contribution of 1-yearstorm

Inland InundationIndex dominated by contributions of 5and 15-year storms

[m-days/yr]

1-2 m-days/yr

Brackish wet sedgemeadow

Correspondence between 1-2 m-day/yr annual Inundation Index and presence of Brackish Wet Sedge Meadow in current climate

[m-days/yr]

1-2 m-days/yr 1-2 m-days/yr

7 km translation of 1-2 m-days/yr annual Inundation Index region – suggesting a similar shift in the location of the Brackish Wet Sedge Meadow vegetation type

[m-days/yr] [m-days/yr]

Annual Inundation Index – current climate Annual Inundation Index – future climate

Conclusions

• Preliminary model validation efforts indicate that the model works reasonably well for 1-yr storm.

• The annual inundation index was well-correlated with vegetation type.

• The annual inundation index increased significantly with the assumed 0.4 m sea level rise.

• Significant shifts in vegetation are expected with a 0.4 m sea level rise.

Future Work• Include wind and wave action in storm surge model.• Do additional model validation including use of aerial images

of inundation extent to calibrate overland flow roughness.• Study additional storms and calculate return period of those

storms at the Kashunuk River mouth.• Analyze the relationship between annual inundation index

and vegetation type more precisely.• Examine the relationship between inundation index and

bird/nest abundance.• Model and analyze pond water quality.• Model and analyze geomorphic change.

Collaborators and supporters

• Craig Ely, John Terenzi (USGS, Alaska)• Torre Jorgenson (Ecoscience)• Raymond Chapman, Ken Eisses (USACE)• Steven Gray (USGS AK Climate Science Center)• Joel Reynolds, Karen Murphy (Western Alaska

Landscape Conservation Cooperative)• Sarah Saalfeld (USFWS)

Questions?