On February 20, 2007, 7:00 pm (Churchill Jr high) a 2 hour meeting will be held in order to provide information and allow for a Q & A period. Based upon the concerns identified, further meetings will be help to allow all parties to educate themselves and develop an informed opinion as to risks related to no action, not building the dam or building the dam. Discussions included the size of the existing FEMA flood Zone A and the UGS mapped flood plain. The FEMA zone is a conservative estimate of homes (approx 150) that would be affected by a worse case flood and debris flow. The UGS map may include approx 300 homes. SL County Flood Control now indicates that 100-year stream flows at the mouth of Neffs Canyon could approach 300 cfs (1 cfs = approx 400 gal). or 2x times the existing channel capacity of 100 cfs.
Update -- December 1, 2007 Mayor Corroon states:
"... our government at this time does not intend to undertake the project you mentioned. We will be undertaking non-controversial projects downstream. We would like the community to come up with a consensus on what it would like to do further upstream but at this time there does not appear to be any kind of consensus".
Review & read the County's study (Neffs Canyon Study)
FEMA Map No. 49035C0317 E. Click on the map near I-215 and Mt Olympus, keep clicking until you see the
"rabbit ears" (Slco.org FEMA map)
What will the dam look like Dam description
Questions & Answers (Q & A's )
Mill Creek Journal Published Articles (news)
Letters (Letters against the proposal)
Earthquake concerns & maps. Earth quake Concerns
Is The Dam Necessary?
We don’t know at this point. FEMA's guidelines state that due to the complex nature of
alluvial fans, studies must be made on the individual fans. No study has been done on
Neffs Canyon. Only a report, which is not enough to base a project on.
FEMA's guidelines for Alluvial Fan studies state:
"Flooding on alluvial fans can only be evaluated on a site-specific basis. On-site
evaluation of the flood hazard requires field investigations by specialists experienced
in the scientific study of alluvial fan processes and the geomorphologic indicators of
their present and past operation. Such on-site investigation is critical to provide a
scientifically sound basis for hazard delineation and regulation." see FEMA Study
Has the County conducted such studies ? Not yet.
Salt Lake County Flood Department states that existing
runoff stream channels are deemed adequate for 100-year-
snow-melt run off levels (estimated to be 100 cubic feet per
second (cfs), 1 cfs = approx 400 gal). see pictures of
(peak snow melt)
The light blue line is the existing channel, the lighter blue
line is the historical channel.
The County's study suggests a 100 year event with maximum of 300 cfs of water. The
maximum theoretical debris flow could reach a level of 150,000 cubic yards (150,000
cubic yards * 27 cubic feet per yard divided by 43,560 feet per acre = 92 Acre feet) or 5
times the proposed size.
The County's study states that any debris flows, that originate in the upper reaches
(above 6,800 feet) of the canyon may not even reach the mouth of canyon due to the
level grade. Pure conjecture by the County. (see pages 11 -15 of the debris Flow Hazard
Study Report)
The U.S. Forest Service has jurisdiction over the Neffs Canyon area. Let them know
that you do not want a dam in the mouth of Neffs Canyon.
Voice your opinion What can I do to help