C150104 Feasibility Study - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I II. Project Parameters A. Site Hydrology The size of the impoundment will make this structure a jurisdictional dam regulated by the State Engineer. The designation as a jurisdictional dam will require addressing such issues as dam hazard classification and probable maximum flood criteria. The location of the project is in an area where it is highly probable the dam will be classified as a Class 3 low hazard structure. This classification is given for sites where there is a low probability for loss of life or damage to property. The reservoir site is off channel and therefore does not intercept any major drainage basin. The proposed design using a ring dike will prohibit any upstream drainage from entering the reservoir. This will greatly reduce the size requirements for the spillway, which will result in cost savings. The flood criteria for the South Platte River would likely show that failure of this structure would have minimal impacts downstream. B. Water Diversions/Delivery There are two options that were explored for the delivery of water from the South Platte River to the proposed reservoir site. The Peterson Ditch is a left bank diversion from the South Platte River that passes to the north of the proposed reservoir site. The Peterson Ditch has the option of diverting flows directly from the river or being supplied from three high capacity wells owned by GASP, which are located near the diversion structure. The Peterson Ditch is owned and operated by the Jules burg Irrigation District. A new structure to release water from the ditch would be installed near the northeast comer of the reservoir. This structure would have a capacity in the range of20 to 40 cfs depending on final project configuration. It is anticipated that a carriage charge will be required by the Jules berg Irrigation District for the use of their stru<;ture. The typical charge runs around $4 per acre-foot based on other users that have agreements with the ditch company. The Peterson Ditch is an earthen channel structure that passes just to the north of the proposed reservoir site. A preliminary survey investigation indicated that there is a sufficient change in elevation between the ditch and the reservoir to allow for gravity diversions from the Peterson Ditch. Based on a preliminary survey of the Peterson Ditch and the reservoir area, gravity diversions from the ditch can be utilized to efficiently fill the reservoir to a stage approximately 2-3 feet below the high water line. The preliminary layout of the reservoir has a high water line at an elevation of 3,566 and a storage capacity of 2,229 acre-feet. The gravity diversions from the Peterson Ditch would be capable of filling approximately 1,700 acre-feet. The remaining storage in the reservoir, approximately 500 acre-feet, will need to be filled from tht:: "Ovid Wells" or another source with adequate head. A conversation with the operator of the Peterson Ditch revealed no apparent conflicts if the ditch was utilized for a winter fill of the reservoir. The only other diversion below the proposed project, that is active during the winter period, is the diversion for the Lower South Platte Recharge project. The Lower South Platte Recharge site is capable of diverting 30-40 cfs (limited by the capacity of the recharge site). The operating capacity of the Peterson Ditch, according to the ditch rider, is approximately 90 cfs. The ditch rider indicated that the limiting factor for ditch capacity is bank erosion in the steeper sections of the ditch near the headgate. The capacity of the ditch increases above the proposed release structure. There are several inflow points upstream that capture stormwater which flows down the ditch. There may be some opportunity to divert these stormwater flows if water quality and administration issues can be adequately addressed. 4