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CHAPTER 12. LANDSLIDE <br />12-9 <br />County Code (Title 17A.06) as well as by the International Building Code. Development will occur in <br />landslide hazards within the planning area, but it will be regulated such that the degree of risk will be <br />reduced through building standards and performance measures. <br />12.8. SCENARIO <br />Major landslides in Kittitas County occur as a result of soil conditions that have been affected by severe <br />storms, groundwater or human development. The worst-case scenario for landslide hazards in the planning <br />area would generally correspond to a severe storm that had heavy rain and caused flooding. Landslides are <br />most likely during late winter when the water table is high. After heavy rains from November to December, <br />soils become saturated with water. As water seeps downward through upper soils that may consist of <br />permeable sands and gravels and accumulates on impermeable silt, it will cause weakness and <br />destabilization in the slope. A short intense storm could cause saturated soil to move, resulting in landslides. <br />As rains continue, the groundwater table rises, adding to the weakening of the slope. Gravity, poor drainage, <br />a rising groundwater table and poor soil exacerbate hazardous conditions. <br />Mass movements are becoming more of a concern as development moves outside of city centers and into <br />areas less developed in terms of infrastructure. Most mass movements would be isolated events affecting <br />specific areas. It is probable that private and public property, including infrastructure, will be affected. Mass <br />movements could affect bridges that pass over landslide prone ravines and knock out rail service through <br />the county. Road obstructions caused by mass movements would create isolation problems for residents <br />and businesses in sparsely developed areas. Property owners exposed to steep slopes may suffer damage to <br />property or structures. Landslides carrying vegetation such as shrubs and trees may cause a break in utility <br />lines, cutting off power and communication access to residents. <br />Continued heavy rains and flooding will complicate the problem further. As emergency response resources <br />are applied to problems with flooding, it is possible they will be unavailable to assist with landslides <br />occurring all over Kittitas County. <br />12.9. ISSUES <br />Important issues associated with landslides in Kittitas County include the following: <br />• There are existing homes in landslide risk areas throughout the county. The degree of <br />vulnerability of these structures depends on the codes and standards to which the structures <br />were constructed. Information to this level of detail is not currently available. <br />• Future development could lead to more homes in landslide risk areas. <br />• Mapping and assessment of landslide hazards are constantly evolving. As new data and science <br />become available, assessments of landslide risk should be reevaluated. <br />• The impact of climate change on landslides is uncertain. If climate change impacts atmospheric <br />conditions, then exposure to landslide risks is likely to increase. <br />• Landslides may cause negative environmental consequences, including water quality <br />degradation. <br />• The risk associated with the landslide hazard overlaps the risk associated with other hazards <br />such as earthquake, flood and wildfire. This provides an opportunity to seek mitigation <br />alternatives with multiple objectives that can reduce risk for multiple hazards.