Alaska Climate Change Impact Mitigation Program Community Planning Grants: Atmautluak After completing a Hazard Impact Assessment (HIA), the Atmautluak Traditional Council was awarded a $150,000 State Fiscal Year 2011 Community Planning Grant to address one or more of the recommendations from the Atmautluak HIA. The Atmautluak Traditional Council selected two recommendations from the HIA to pursue: (1) to conduct a hydrological study of the Pitmiktakik River and, (2) to develop a community surface drainage plan. Both of these recommendations were combined as one study, the Atmautluak Hydrological Study and Community Drainage Plan. This study was completed by AECOM on June 27, 22016. The purpose of the Atmautluak Hydrological Study was to determine the recurrence intervals of floods and provide a hydrological basis for the evaluation the existing bank erosion and proposed alternatives to reduce bank erosion along the Pitmiktakik River. Two areas on the shore of the larger lake west of the town were also studied.The purpose of the Community Drainage Plan (which is was to identify alternatives that could drain excess surface waters at Pig Lake to nearby lakes and rivers in order to restore natural drainage, reduce flooding of properties in spring and fall, and reduce heat transfer to underlying tundra from standing water, which could potentially decrease permafrost degradation. The study found that erosion is primarily due to hydraulic shear stress on fine grained soils, with soil pore pressures and ice scour also contributing. Bank stability and reduced erosion can be achieved with installation of a sheet pile wall, articulating concrete block matting, or a cellular confinement system. Articulating Concrete Block matting is the recommend alternative. A sheet pile wall would be more expensive than the other options and would be subject to corrosion. Articulating Concrete Block matting or a cellular confinement system would provide easier boat access than a sheet pile wall. A cellular confinement system would be susceptible to ice damage and was not recommended. A new drainage swale can be constructed from Pig Lake to the north to restore natural drainage and keep the water levels in Pig Lake as low as possible. Atmautluak Community Planning Grant Documents Atmautluak Hydrological Study and Community Drainage Plan Atmautluak Hazard Impact Documents Atmuatluak Hazard Impact Assessment Erosion Information Paper - Atmautluak, Alaska (USACE) Background Atmautluak (pronounced aht-MOUTH-luck), 2010 population 277, is located on the west bank of the Pitmiktakik River in the Yukon-Kuskokwim Delta regional basin, 20 air miles northwest of Bethel. The community is in the Unorganized Borough. The entire length of the community is subject to erosion, which is caused by natural river flow, spring breakup, melting permafrost, boat wakes and ice jams. According to local officials, three to four ice jams have caused 1- 2 feet of erosion per event over the last 10 years. The Pitmiktakik River, a tributary of the Johnson River, erodes approximately 1 foot per year. Community officials report that the river bank and surrounding ground used to be higher but is sinking due to melting permafrost. The lake shore is also eroding due to melting permafrost and occasional strong south winds. The Atmautluak Hazard Impact Assessment, completed in June 2010 by WH Pacific in partnership with Shannon & Wilson, recommends several measures by which Atmautluak can address its hazard impacts: Conduct a hydrological study to quantify recurrence intervals of floods and to evaluate alternatives to reduce bank erosion Require that future projects install thermistors to document changes in the active layer Monitor erosion through bank migration study (aerial photographs and physical measurements) Raise fuel lines off ground to reduce susceptibility to subsidence and subsequent corrosion Prepare community land use plan to identify preferred locations for new housing or other community facilities or infrastructure Prepare community surface drainage plan to drain surface water into nearby lakes and rivers Move or replace structures in danger from riverine erosion Eroded riverbank and threatened homes. Photo: U.S. Army Corps of Engineers Atmautluak main point of contact for ACCIMP Community Planning Grant Daniel Waska Tribal Administrator Atmautluak Traditional Council Phone: 907-553-5610 For more information contact Sally Russell Cox Division of Community and Regional Affairs Department of Commerce, Community, and Economic Development 550 West 7th Avenue, Suite 1650, Anchorage, AK 99501-3569 Phone (907) 269-4588 Fax (907)269-4066 Email: sally.cox@alaska.gov