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I I I I I I I I I I I I I I I I I I I Mr. Ben Ur bonas September 12, 1984 Page Five Mr. Ben Urbonas September 12, 1984 Page Six bodies of the local governments, needs to be well-documented so subsequent public officials will understand the criteria and basis for the decision. In my opinion, the legislative bodies have the authority to make such decisions but damaged property owners (in times of greater flooding) will almost assuredly make claims for "undersizing" or "inadequate" drains against the local governments involved. My comments regarding the channelizing of some portions of Ralston Creek in owners' backyards, are appli- cable to some portions of Leyden Creek as well. SUMMARY: Hopefully, the Oak Street detention facility will eventually be built which, according to the engineer, will provide 100-year level protection through the Arvada Shopping Center. The legal principles applicable to dams are also applicable to detention ponds. 1. Whatever improvements are undertaken, the local governments must know that they will be held to the standards of a private party. The local governments do not have to do anything not caused by their negligence. If they choose to, however, they will be held accountable for their negligence. c. Leyden Creek - The most far reaching recommen- dation here, and perhaps of the total Report, is the pro- posed rehabilitation of Leyden Lake, including the dam and spillway. The current dam is "high hazard" as defined by the criteria of the State Engineer (as well as USBR and USACE). The Lake is a component of the Farmers Highline Reservoir and Irrigation Company. The City of westminster currently controls this flood control and storage facility. However, most damages that would be associated with its failure would be in the City of Arvada. Leyden Lake is currently under a restriction imposed by the State Engineer due to dam safety concerns. Because of these and other facts, the State Eng ineer is rating the dam as "high hazard" compared to a previous "moderate hazard". 2. Upstream improvements must be made taking into consideration downstream outlet capabilities. 3. If Leyden Lake is rehabilitated, maintenance of the improvements must be assured, as with all other improvements constructed in connection with solving drainage problems. 4. The success, as well as necessity, for all con- structed drainage facilities is the ability to show that a problem situation was improved but not by creating a problem for someone else. The engineer recommends constructing a spillway near the left abutment which would be able to convey the probable maximum flood of 19,000 c.f.s. without overtopping the em- bankment. The spillway would be of concrete with a width of 280 feet (see section VI-9 of the Report). The purpose of the proposed rehabilitation cost of $2,649,000 would be to provide present worth benefits (decreased damages in the event of flooding) of $14,000,000. Repairing the I,ake to State Engineer specifications would also provide storage benefits to the owner. In the event a joint project were undertaken, as recommended by the engineer, portions of the costs associated with flood control benefits would have to be identified, as distinguished from storage benefits (additional four feet). If you have any questions related to the above, please let me know. JS:rch Yours ver truly, ~hoem"'e'