WSP01817

• File Number: 8443.400
• Description: Narrows Unit - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 6/1/1983
• Author: US DoI BoR
• Title: Addendum No 2 to Definite Plan Report
• Water Supply Pro - Doc Type: Definite Plan Report

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CHAPTER III - CURRENT PLAN

NARROWS DAM AND SPILLWAY

Narrows Dam will be a zoned earthfill structure located 7 miles

'.

northwest of Fort Morgan, Colorado. The dam will have a maximum

structural height above streambed of 133 feet, a crest length of

18,000 feet, and a crest width of 30 feet. A 6,OOO-foot-long sl urry

trench, a minimum of 5 feet into the Pierre Formation, will be con-

structed in the middle one-third of the dam to control seepage. A

cutoff trench to the Pierre Formation, 5,600 feet long, will be con-

structed on the 1 eft or northern port ion of the dam. Seepage under
the cutoff trench wi 11 be controlled by a single row of 60-foot-deep
grout holes on 10-foot centers and blanket grout i ng with 30-foot-deep
holes on lO-foot centers under the core. A 3-foot-thickness of soil-

cement will be placed for upstream slope protection and 1 foot of seeded

topsoil will be placed on the downstream slope.

The max imum reservoi r water surf ace e 1 ev at i on will be 4433.3, and the

total controlled capacity will be 656,000 acre-feet at elevation 4413.8

(figure 3). The service spillway, with a crest elevation of 4395, will

have two 25-foot-wide radial gates sized to satisfy flood control

release requirements. The auxiliary spillway, with a crest elevation

of 4415.5 and a length of 1,500 feet, will operate only during major

floods. The river out let works will have a capacity of 5,000 ft3(s

within the exclusive flood control pool (elevation 4399 to 4413.8) and

2,000 ft3(s at elevation 4351 to provide for normal river releases and

for evacuation of the conservation storage pool.

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