157.261 Geologic investigation.
(A) The following are geologic hazard areas to which the standards of this section apply:
(1) Active landslides identified in State Department of Geology and Mineral Industries (DOGMI) Bulletins 74 and 79;
(2) Inactive landslides, landslide topography and mass movement topography, identified in DOGMI Bulletins 74 and 79 where slopes are greater than 20%;
(3) Areas prone to mudflows identified in DOGMI Bulletin 79;
(4) Brallier peat soils identified in Soil Survey, Tillamook Area, Oregon (USDA, Soil Conservation Service, 1964) and the unpublished Soil Conservation Service soils survey for coastal Tillamook County; or
(5) Other locally known areas of geologic hazard based on evidence of past occurrences.
(B) All development within geologic hazard areas shall comply with the following standards.
(1) Vegetation removal shall be the minimum necessary to accommodate the use.
(2) Temporary measures shall be taken to control runoff and erosion of soils during construction. Such measures include temporary stabilization (mulching or sodding), sediment basins or other performance equivalent structures required by the city.
(3) Exposed areas shall be planted in permanent cover as soon as possible after construction.
(4) Storm water shall be directed into drainages with adequate capacity so as not to flood adjacent downstream properties. Finished grades should preferably be designed to direct water flows along natural drainage courses.
(5) Additional requirements contained in a geologic report required by this section shall be followed.
(C) A geologic hazard report is required prior to approval of planned developments, subdivisions and partitions governed by Ch. 156 of this code of ordinances, building permits, manufactured home permits, mining and excavation occurring in areas identified in division (A) above.
(D) A report prepared for a subdivision, planned development or partition pursuant to the requirements of this section, may be used to satisfy these requirements for subsequent building, mobile home or manufactured home permits; providing that, the original report provided recommendations on building placement and construction and that these recommendations are followed.
(E) The geologic hazard report shall be prepared by a geologist, engineer, engineering geologist or other person having professional experience analyzing the relevant geologic hazards.
(1) Structural recommendations must be stamped by a registered professional engineer.
(2) The boundaries of the study area shall be determined by the city.
(3) It shall be prepared in a format easily understood by a “lay-person” and shall include plan and sectional diagrams of the area showing property boundaries and the geographic information required by division (F) below.
(F) The geologic hazard analysis shall include the following:
(1) In landslide areas (divisions (A)(1) and (A)(2) above):
(a) Soils and bedrock type;
(b) Slope;
(c) Orientation of bedding planes in relation to the dip of the surface slope;
(d) Soil depth;
(e) Other relevant soils engineering data;
(f) Water drainage patterns; and
(g) Identification of visible landslide activity in the immediate area.
(2) In areas prone to mudflow (division (A)(3) above):
(a) History of mud or debris flow; and
(b) Areas likely to be affected by future mudflow.
(3) In Brallier peat soils (division (A)(4) above):
(a) Boring log or other similar measure;
(b) Bearing capacity; and
(c) Drainage patterns.
(G) The geologic hazards report shall recommend development standards that will protect development on the property and surrounding properties. These should include standards for:
(1) Development density (when more than one use is possible);
(2) Locations for structures and roads;
(3) Land grading practices, including standards for cuts and fills;
(4) Vegetation removal and re-vegetation practices;
(5) Foundation design (if special design is necessary);
(6) Road design (if applicable); and
(7) Management of storm water runoff during and after construction.
(H) The geologic hazard report shall include the following summary findings and conclusions:
(1) The type of use proposed and the adverse effects it might have on adjacent areas;
(2) Hazards to life, public and private property, and the natural environment which may be caused by the proposed use;
(3) Methods for protecting the surrounding area from any adverse effects of the development;
(4) Temporary and permanent stabilization programs and the planned maintenance of new and existing vegetation;
(5) The proposed development is adequately protected from any reasonably foreseeable hazards including, but not limited to, geologic hazards, wind erosion, undercutting and flooding; and
(6) The proposed development is designed to minimize adverse environmental effects. (Ord. 80-2, passed 06/14/2010)