WSP07896

• File Number: 8449.600
• Description: Chatfield Reservoir
• State: CO
• Basin: South Platte
• Date: 2/1/1976
• Author: M W Bittinger & Asso
• Title: Preliminary Feasiblity Estimate of the Potential Use of the Conservation Pool of Chatfield Reservoir
• Water Supply Pro - Doc Type: Publication

The days when there were no demands by any priorities were summarized

from the call record. For these days total inflow was determined from the

recorded flows of the South Platte River, Plum Creek, Bear Creek; Clear Creek,

and the St. Vrain, Big Thompson and Cache la Poudre Rivers. The filling rates

of the reservoirs were established for the same call-free periods, and their

storage diversions were subtracted from the total inflow. The amount of

excess flow at the Chatfield site was then regarded as storable water for

the 1975 priority.

In satisfying the downstream reservoir demands no consideration has been

given to return flows reaching the river between Chatfield Reservoir and their

respective headgates. The intentional neglect of this supply places the

arrived estimates of storable water on the conservative side.

Similarly the effect of other operational characteristics has been

omitted from consideration. Since 1969 the practice of filling the reservoirs

in a downstream order, rather than in their priority, has become the pr~ctice

more often than it was prior to that year. This practice eliminated certain

calls for water by dOlnlstream reservoirs in the off-season period and at the

same time stored w~ter in upstream reservoirs on a conditional basis. The

rationale behind this operation is the anticipation that downstream reservoirs

will be able to fill from the spring runoff, from return flows, or from local

precipitation events. The water retained conditionally at higher elevations

will give these lower water rights the assurance that in case their'priority

could not be satisfied from the above-named sources, part of the conditionally

held water could be released for their satisfaction. This practice is extremely

important and beneficial for all the water users in the basin; however, its

effect cannot be estimated to any degree of accuracy due to the short period

of record.

To estimate the effects of presently conditional water rights becoming

active at a later time is quite difficult and requires certain assumptions to

be made. Basically two proposed reservoirs must be considered in this category--

one being Two Forks above Chatfield, and the other one Narrows just above Fort

Morgan. For Narrows it is probably correct to assume that since the District

is the owner of more water in this reservoir than the space available in Chat-

field, either Narrows will not callout Chatfield to the extent it can store

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M, W. BITTINGER AND ASSOCIATES. INC.