ML20206L767

Submits Addl Info in Response to Questions on Geosciences Program Clarifying Rates of Erosion Along State of or & State of Wa Coastlines Re Formation of Modern Wavecut Platforms.Questions Arose from NRC Sept 1988 Visit

ML20206L767
Person / Time
Site:	Satsop
Issue date:	11/21/1988
From:	Sorensen G WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
GO3-88-283, NUDOCS 8811300235
Download: ML20206L767 (4)

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, WASHINGTON PUBLIC POWER SUPPLY SYSTEM P.O. Box 968

• 3000 George Washington Way

• Rkhland, Washington 99352 i

Docket No. 50-508 l

November 21, 1988 G03-88-283 U. S. Nuclear Regu13 tory Commission P1-137 Washington, D. C. 20555 Attention: DOCUMENT CONTROL DESK 9

Subject:

NUCLEAR PROJECT N0. 3 i

RESOLUTION OF XEY LICENSING ISSUES RESPONSE TO QUESTIONS ON GEOSCIENCES PROGRAM In response to informal questions posed by the NRC Geosciences staff 4~ _

members, we are submitting additional information for your consideration during the WNP-3 review. The information submitted clarifies the rates of

'- erosion along the Oregon and Washington coastlines as it pertains to the formation of xdorn wavecut platforms. These questions originated during discussions held in September 1988 during an NRC site visit.

We look forward to discussing this with you as soon as you have completed your review. If you have any questions, please contact Mr. Richard j Latorre, Corporate Licensing & Environmental Manager at (50.?) 372-5304.

Very truly yours,

b i G. C. Sorensen, Manager

Regulatory Programs cc: MF Barnoski/CE I WC Brauer/PP&L l WL Bryan /WP DW Cockfield/PGE l WJ Finnigan/ PSP &L C Goodwin/PGE i JR Lewis /8PA 399 JB Martin /NRC Reg. Y

R McMullen/NRC S Prussman/Ebasco NY L Reiter/NRC

NS Reynolds/BCP&R R Rothman/NRC ol RM Taylor /Ebasco - Elma/705 go }i l G. Vissing/NRC , g i Ebasco/NY J

8811300235 881121 1

PDR ADOCK 05000508

-_ ___A _._ _ _ PNU_ _ . _ _ _ _ _ _ _ , _ _ _ _ _

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O Golder Associates CONSULTING GEOTECHNICAL AND MINING ENGINEERS October 14, 1988 Our ref. 863-1148 Washington Public Power Supply System 3000 George Washington Way P.O. Box 968 Richland, Washington 99352 ATTENTION: Mr. William Kiel RE: COASTAL EROSION RATES ALONG OREGON AND WASHINGTON

Dear Bill:

I have briefly examined the rates of erosion along the Washington and Oregon coasts in order to get an idea of the amount of time it would take to produce the broad, rocky, modern wave-cut platforms that we have observed. The modern wave-cut platforms are generally about 100-300 m wide, although we have not made precise measurements of their widths. In addition, they occur at rocky headlands along all of the coastline, whether it is 60 km from the trench (cape Blanco) or 130 km (Pt. Grenville). The modern platforms are cut in Tertiary sandstone, siltstone and basalt.

Sparks (1986) has noted that the factors that influence the nature and rate of coastal eroeion include:

• the nature of the bedrock being eroded such as: hardness, comentation, reaction to chemical weathering, and frequency of faults and joints; soft, weakly cemented, unconsolidated rock is easily eroded and high fracture frequency leads to faster erosion.

• the height of the cliff being eroded; the higher it is the slower the rate of erosion.

• orientation of the coastline with respect to the dominant waves; waves that break head-on result in higher rates of erosion.

• nature of longshore drift; if it is effective at removing the eroded material, then it allows erosion to proceed more readily.

McDowell (1987) has examined the geomorphic processes along the Pacific coast of Oregon and Washington and has noted GMt9 ASSociatt$ tNC . 333 >tGENetectm poso svitt M CA%AND C AUFCnN' A $4429. U S A . f tLINCNE #4551635 4143 f tLtF A R i419t t3S 1879 CFF <tl

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that coastline retrogression or progression is related to i

, eustatic sea level rise, tectonic uplift, and sediment supply to the littoral zone. McDowell (1987) notes that both retreat of the coastline and a stable coastline are found today along Oregon and Washington, but that most of the coast appears to be stable. She has listed the rates of coastline erosion based on the bedrock type and these are summarized as follows:

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Erosion Bedrock Rate, cm/yr Erosional Process Pre-Tertiary <5 Blockfalls; slumps, earthflows Tertiary 2-60 Rockfalls; debris slides Sandstone Tertiary 12 Slumps; flows, shifts Siltstone Tertiary very slow Rockfalls; debris slidas Basalt (<5 ?)

From the above rates, and given the rock types along the coast, plus the widths of the modern platforms (100-300 m),

the amount of timo to create the platforms varies from a low of about 170 years to a high of 15,000 years. The lowest amount of time is based on using the highest rate of erosion (60 cm/yr) over the thinnest platform (100 m). Since the highest rate of erosion would be associated with the least indurated bedrock, and since the bedrock observed appeared to be indurated, this time (170 yrs) may not be representative. The coastline erosion rates of about 5-12 cm/yr may be more representative of the long-term averago given the present stable nature of most of the coast and the induration of the bedrock at the sites of the broad platforms. Thus, the amount of time to produce a broad, rocky, modern wavo-cut platform may be on the order of 800-6,000 years (ratos of 5 and 12 cm/yr over widths of 100 and 300 m).

References:

McDowell, P.F., 1987. Geomorphic processes in the Pacific Coast and Mountain system of Oregon and Washington: in Geomorphic Systems of North America, (ed) W.L. Graf, Geological Society of America Contonnial Special Volume 2,

p. 539-549.

Sparks, B.W., 1986. Geomorphology: Longman Group, Ltd.,

London, Third Edition, 561 p.

Golder Associates

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. Please call if you-have any questions.

- Sincerely, GOLDER ASSOCIATES INC.

Mt Donald O. West Associate DOW:dow cc: D. Caldwell i L

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