Two videos portraying coincident flooding of Silver Creek and Tenmile Creek

Following a large flood event in 2011, Lewis and Clark County embarked on a comprehensive flood mitigation planning effort. The “Valley Flood Mitigation Master Plan for the Helena Valley” (VFMMP) was finalized in April 2013. The document summarizes large scale flooding issues and proposes conceptual-level solutions to manage floodwaters throughout the valley. The overarching goal outlined in the Master Plan is to convey and detain floodwaters in a controlled manner, to reduce the frequency and magnitude of flooding homes, businesses, and transportation corridors.

The first task for implementation of VFMMP projects is to develop a detailed hydrologic and hydraulic analysis for the two primary flooding sources in the Helena Valley: Tenmile Creek and Silver Creek, in addition to final design, permitting, and construction of the Trap Club flood detention project. The goal for the detailed hydrologic and hydraulic analysis is to better understand quantity, timing, and flow patterns throughout the Helena Valley, essential for planning, designing, and constructing flood control infrastructure. Additionally, the focus of the detailed study is to ensure infrastructure improvements do not adversely affect property owners within the planning area.

4% annual chance event (25-year)

1% annual chance event (100-year)

DISCLAIMER: THESE SIMULATIONS REFLECT PRELIMINARY RESULTS FROM THE STUDY FOR THE 4% ANNUAL CHANCE EVENT (25-YEAR) AND THE 1% ANNUAL CHANCE EVENT (100-YEAR). THIS MAPPING IS FOR PLANNING PURPOSES ONLY AND IS NON-REGULATORY. THE CONDITIONS PORTRAYED ON THIS MAP REFLECT: COINCIDENT FLOODING OF TENMILE CREEK AND SILVER CREEK, THE ACCURACY OF THE TOPOGRAPHIC DATA INPUT, AND THE LEVEL OF DETAIL WITHIN THE SUPPORTING HYDRAULIC MODEL. ACTUAL FLOOD CONDITIONS MAY DIFFER FROM THIS MAP.