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<br />were adequate, substantial spilling would not he ~ossjhle
<br />without some damage. A failure by overtopping would be
<br />disastrous. Complicating this problcm is the fact that
<br />a certain amount of the input into East Reservoir, whiCh
<br />is in the Weir Gulch Basin, comes artificially from the
<br />discharge from Smith Reservoir in Sanderson Gulch,
<br />
<br />these situ~tions ~re ~ublic street crossings, some of whiCh
<br />are state highways, In at least onc important case, at
<br />the entrance to Green Gables Ccuntry Club, a private
<br />roadway fill is involved. A major distinction betwc<ln
<br />the "non-intentional" dam and the other dams is that the
<br />bed of the reservoir is not necessarily owned by the owner
<br />of the structure and at least not for reservoir purposes.
<br />In the case of Gree~ Gables, however, the upstream land
<br />is part of the natural gulch within the golf oours?, The
<br />use for short term retention is not incons~stent w~th the
<br />existing land use. A feature of these structure7, of
<br />course, is that they do not have decreed water,r~ghts and
<br />are not regulated by state agencies as reservo~rs,
<br />
<br />2. Recreation Pools in Park Developments
<br />
<br />Several of the smaller reservoirs along the channels are
<br />owned by public parks. In addition at least one large
<br />one, Kendrick Reservoir and also Kendrick Lake No. 1 which
<br />has been a large structure, both in the upper reaches
<br />of Sanderson Gulch, are owned by the Foothills Park and
<br />Recreation District. The latter structure is not being
<br />used for impoundment presently as the park is using small
<br />pools in the old lake bed for recreatiOn purposes. Sub-
<br />stantial flood detention still remains behind the currently
<br />existing structure.
<br />
<br />5. Irrigation Ditches
<br />A somewhat different type of situation e~ists where an
<br />irrigation ditch crosses the natural dralnage and has
<br />historically taken, under rural condit~ons at least, a,
<br />portion of the flood flows, The notable example of th~s
<br />is the Agricultural Ditch where it crosses.sande7so~ GU~Ch
<br />at Estes Pond. In addition to gulch cross~ngs, ~rr~gat~on
<br />ditches may have taken storm flows from the unconcentratcd
<br />diffused surface flow from adjacent slopes.
<br />
<br />3. Private Pools for Aesthetic Purposes
<br />Several small reservoirs exist along the main stem of the
<br />Sanderson channel whieh are privately owned. Several of
<br />these happen to be strategically located for small volume,
<br />short term flood detention purposes, and their existence
<br />is a key factor in the existing channel char~eteristics.
<br />Primarily, these are for aesthetic and recreation purposes
<br />only. No significant amount of water is used for irrigation
<br />from them. Included among these are Clairfield Reservoir
<br />and Bit-O-Sea Reservoir. The latter is privately owned by
<br />a corporation comprised of adjacent property owners.
<br />
<br />~hc structural stability of Lhese reservoirs is primarily
<br />a q;,;cstion of hydrologic rioik. Som., flood 'within lh.. u",,,,i,,,n
<br />parameters will cause overtopping and, presumptively,
<br />structural failure, The use of a small increment of short
<br />term storage capacity for flood detention would not be in-
<br />ronsistent with the current use, but some physical improve-
<br />ments would be required by the IOO year design frequency
<br />criteria.
<br />
<br />In general, these facilities do not represent an extremely
<br />valuable function in the storm drainage performance of the
<br />basin, primarily because they were not so intended. The
<br />ultimate release of storm waters so taken may not be a~y
<br />nearer to the main urban flood channel at the South Platte
<br />River. The available capacity is not necessarily large
<br />and does vary substantially depending on the irrigation flow
<br />at the time. The discharge of storm waters may well result
<br />in a breaching of the ditch's bank at some disadvantageous
<br />point along its route. The,conditions under WhlCh s~Ch a
<br />ditch has historically rece1ved storm flows have rad~cally
<br />changcd with the urbanization of tributary arcas. Prcsently
<br />certain physical changes would need to be made to prevent
<br />storm ,^'aters from entering the Agricultural Ditch.
<br />
<br />Th", p~.iUL'Uy ",)\,111\[.>1<< of thi... com:"'pt: i" a roa.dway fill
<br />cross~ng the natural drainage. Water does not normally
<br />and was not intended to back up behind the structure, but
<br />in time of flood of d given size the culvert capacity is
<br />insufficient to pass the flow without submergence and signi-
<br />ficant short term flood det"ntion occurs, The mi),jority of
<br />
<br />THE USE OF FLOOD PLAIN ZONING TO CONTROL
<br />EXISTING CHANNEL FEATURES
<br />It is our opinion that flood plain zoning based on the Flood Plain
<br />Regulation as adopted by the Urban Drainage and Flood COntrol
<br />District i... August, 1970, is a valid, necessary and valuable step
<br />in maintaining existing hydrologic characteristics in SanderSOn
<br />and Weir Gulches. On the other hand. we think it is inadequate
<br />to give sufficient perpetual control of the various reservoirs which
<br />provide important flood retention.
<br />
<br />4. "Non-intentional Dams"
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