8-13D-9-14: GEOTECHNICAL CHARACTERIZATION:

Development of the geotechnical constraints characterization was designed to help recognize factors inherent to natural features which would potentially affect project planning, development and construction. The Boise foothills are prone to some geotechnical constraints which are characterized by slope failure, over-steepened slopes, excess hillside erosion and uncontrolled flooding.

Slope stability and expansive soils associated with the Boise foothill's volcanic assemblage as a geologic unit is known for its potential for both shallow (translational) and deep-seated (rotational) slope failures. The lower stratigraphic sequence of the volcanic assemblage is characteristic of low shear strength, especially along interface clay layers within the lower Terteling Springs Formation. The expansive (swelling) soils are readily recognized by the chocolate brown color and mud-cracked surface, and occurrence of these soils is confined to the outcrop area of the volcanic assemblage. It is believed clayey soils in these areas may have excessive low shear strength when saturated. In addition, the clays tend to have poor drainage, and some are moderately expansive.

   1.   Minimize the detrimental effect of natural constraints to the health, safety, and general welfare of the Hidden Springs project in individual site acquisition and/or development of real property; and

   2.   Encourage the most beneficial use of selected development areas and productive development of sites within each area.

Geotechnical:

The slope map and description included in this Section illustrates and describes areas categorized by the following slopes:

   0-5 percent

   6-10 percent

   11-15 percent

   16-20 percent

   21-25 percent

   over 25 percent

Development of these areas will require more detailed study. Characteristic of severe slope failure, high ground water, over-steepened slopes, and rock topple.

Due to the fact that the basis for this classification is generalized and from secondary sources, the development and platting process as described in Section 4 will require more detailed planning at a site-specific level. At that time, specific building envelopes and lotting criteria will be established to avoid or mitigate identified hazards.

These areas can be developed with some limitations and/or restrictions. These areas may include ancestral slope failure, steep slopes, some swelling or fat clays. The restrictions placed due to the potential hazards are usually not serious enough to prevent development.

These areas can be developed. Little or no development restrictions are associated with these areas. These areas are located primarily south of Dry Creek and Currant Creek.

   Figure 2-H

(Ord. 1002, 10-28-2025)