3829 SHORE AVE 2018-01-02 MF Import

Prioc to the sea wal'_ cc^struction, the area was one of rapid seacliff retreat due to toe erosion from wave activity. A slower rate of backwasting of the slope over time is now considered the primary cond:.tion affecting rel.ative slope atability o£ the area. T.he easierly portion of the slope area (east of approximate STA 24+OJ) has apparently been subject to larger scale slope move- ments, �enerally as indicated wy the m�ny 't�owl' type features � across the area. These larger ecale slope 1'ailures appear to be less rE:cent rotational slumpe which occurre� due to toe eupport removal and slope adjustment. Observed conditions of this area now incicated that the large scale movemente have somewhat atabi- lized, through a combination o£ the mass wasting process, vege- tation,drainage and toe support by the railroad sea Nall. We would not expect signiYicant maes wasting within this area unless ar�y of the above stabilizing features are altered. Presently, only minor areas of aurface slope failures are noted within this area. The westerly portion of the slope area (west of approximately STA 24+00) has been subject to smaller scale, although more recently active, surface slope movements - or earth and debrie flowe. The Whidbey Formation soils which are thicker in this area appear more susceptible to surface failure and upslope erosion than the easterly portion which exhibits a greater thiclmess of Double Bluff drift and talus upon the base of slope. In this weatern portion� many sur£ace failures exist (see location map) �articularly in the central portion where the mos* amount of debris and surface water occurs over the top-oS-slope. No apparent deep seated failures similar to those in the easterly portion were noted. The talus deposits and slide debris are much lese exten- sive or thick near the toe-of-slope. For maintence of the tracks and drainage� slide debris is generally removcd by the Railroad within the ditch along the toe-of-slope. This allows more up- slope material to accumulate in the form of surface earth flows through the normal backwacting process of this area. The combin- ation of debris cOntinued to be placed along the top-of-slope, dr�ins allowed to freely flow over the slope edge and talus/slide debris removed from the slope tne� contribute to continued near -7-