HomeMy WebLinkAboutFort Worden Stairs - 1993.05.00I
NORTHWESTERN
TERRTTOBIES' INC'
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PrePared
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WASEINGTON STATE
PrePared BY
NORTIIIIIEStERN
TERRITOBLES' INC'
l4aY 1'993
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GEOLOGIC CONDIT:EONS
The bluff is under-lain by alluvial sediments transported by outwashstreams from receding glaciers over 12r0OO years igo. The uniformfine to med.iurn grain, nearly clean sands present suggest d,epositionalong ancient shoreline areas. The sand depositJ-und,erfiing ttrebluff are generally dense below abodt one fooi penetration -(Lo6s ofBorings). They are uncemented and subject to erosion and. sloujfringin surface exposures.
The bluff surface is mantled by grass and, brush. Supportive soilon the bluff slope is generally about one foot in thllkness "*""pialong an existing foot path down the slope in the vicinity of tireproposed stairway (Figures 2 and 3). Soit has been worn irom theupper portion of the path. Both the soil and sand. deposits wornfrom the upper portion have accumulated on the lower portion of theslope; these materials are loose and. appear to be up to about fourfeet in thickness (Figures L through 3f.
The bluff has been formed by marine erosion and und,ercutting alongthe shoreline, resulting in over-steepening and periodic surfac6sloughing resulting in slow landward recession of the bluff face.The rate of natural recession of the bluff cannot be estimated riif,accuracy. However, an average annual retreat of one to threeinches per year is not unreasonable. Continual sloughing "ttaerosion of the bluffs throughout the area contribute to'-beachsediments that provide protection to the base of the bluffs againstnormal periodic marine wave and tidal erosion.
Tlr" major portion o.f surface d,rainage of the nearly leve1 areaabove the bluff is generally northwaia or westward away from thebluf f face. No areas of seepage, which might ind.icite gro"rrdmoisture, were observed along the bluff.
CONCTI'SIONS
Construction of a stairway leading down the bluff face is feasible.The bruff is grossly stable and shourd not be subject tosignificant erosion or sloughing where und.erlying sand. depolits areprotected. by grass or low growing brush vegetalion cover. sanddeposits underlying the bluff slopL are dense about two feet belowthe natural slope surface and of adequate strength and. stability tosupport the proposed stairway. The stairway Lonstruction is notanticipated to adversely effect the stabifity of the srope oiadjacent areas
piers supporting the existingimmediately above a portion ofThe bulkhead appears to haveHowever, it appears to be
The depth and conditibn of wood.bulkhead retaining walI that liesthe proposed stairway is unknown.been installed over ten years ago.
use by others or other uses. The observations, interpretations,
and conclusions herein are based on generally accepted professional
engineering and geologic principles and practice. This warranty isin lieu of all others, either expressed or implied.
Blase CylwikEngineering Geologist
Michael J. AndersonProfessional Engineer
fc: WA-Prks.Maydir: Eng/Rpt
E[P. DATE 5.5.