12-09-1985 Council Packet - Laserfiche WebLink

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b. To impruve oc, maintain conulS 1; lake anci the creek, over those which existed 1,rio, truction of the Headwaters Control Structure. SECTION III. UPEHATING IJIWC!_:UUHE: The Headwaters Control Structure Is operated in accordance with this section to accomplish thn Manage:,iient Goals in SECTION II. The operating procedure requires discharges to occur within the limitations of established discharge zo,ies described as function of the Lake Minnetonka level. The ranges of discharise defined by the -e zones are necessary rea1l:::n6 the numerous considerations which must be t,iL.en into ac :ount during operation of the structure. The discharge zones are based upon sound hydrologic principles and are designed to achieve, to the `*eeatest extent possible, the Management Goals iientified in SECTION I1. "'he atta ched exhibit shows the di :ct ,,rt a zones and .heir corr_,poridliL6 allowable: discharge rate. The lowest heavy line across the base of the graph at elevati-n 928.6 represents the minimum lake level elevation at watch discharge can occur. This Is similar to the effect of t:,e previous fixed weir which had an approximate low point elevation of 928.6. When the lake level is above this elevation, a discharge will occur subject to the conditions outlined in this section. The discharge zones are defined by minimum required and/or maximum allowable discharge rates over a specific time period and lake level ranee. These zones are described in SECTIO14 III.A below. Between lake level ele,,gtions 928.6 and 930.0 discharge to Minnehaha Creek will vary. In general, discharge rites wall increa-e as the lake level. increases. However, this Is not a direct or linear relationship. The discharge is dependent not only upon lake level elevation, but the time o: year, climatic conditions, the variable carrying capac'_ty of the crt.:k and other cons ide rat ions . The heavy horizontal line at elevation 930.0 represents a lake level above which high eater will be re('-;^.ed to the maximum, practicable extent. Lame levels and dischart,- .snot be controlled by the structure at lake level elevat ..,s above 930.0. Unuer :.hese circumstances, resulting discharge to Minnehaha Creek Is comparable to that whict, occurred under similar conditions with the previous fixed weir. Uuring the winter nt)nth which are not sh%wn on the attached exhibit, no a-LounarL,e is all d to the extent 1'easible and cons istant with the MANAGEMENT POLICY. Stop lobs are: Installed during the late fall, prior to ice -in when the lake level elevation is near 928.6. The discharge control gates are then lifted out of the water to prevent ice damage. If the lake level rises after that time, additional stop lugs are installed as _j of 1 t