WSP01414

• File Number: 8449.918
• Description: South Platte Projects
• State: CO
• Basin: South Platte
• Date: 8/1/1982
• Author: CWCB
• Title: South Platte River Basin Assessment Report
• Water Supply Pro - Doc Type: Publication

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The flows of the South Platte River at Kersey can be considered to be

representative of the surface water supply available for irrigation in the

lower South Platte River basin. Although the mean annual flow was

534,000 acre-feet during the 1928 through 1979 water year period, flows

have varied considerably from year to year, ever since 1953 (Table 9). The

annual flows have ranged from 160,000 acre-feet in 1955 to about

1.6 million acre-feet in 1973. Streamflows of the South Platte River at

Kersey also have varied seasonally, as shown in Table 10.

Average flows of the South Platte River are compared at the Kersey gaging

station during the periods of the 1928 through 1952 water years versus the

1953 through 1979 water years (Table 8). Flows during the former period

averaged 459,000 acre-feet, while they averaged 604,000 acre-feet during

the latter period. It is likely that much of this increased flow of the

South Platte River at Kersey is attributable to return flows from the

Colorado-Big Thompson Project, reflected as well by flows in St. Vrain

Creek, the Big Thompson River and the Cache 1a Poudre River. Return flows

from this project are considered as native South Platte River basin water.

The reach of the South Platte River from Kersey to Julesburg is about

150 miles in length. The mean annual flow of the South Platte River

downstream from Kersey reaches a minimum at Balzac, where the mean annual

flow has been 267,000 acre-feet during the 1928 through 1979 water year

period. The annual flow at Balzac was nearly the same as the mean annual

flow at Henderson during this same time period (Table 8). The mean annual

flow of the South Platte River at Julesburg was about 314,000 acre-feet

during the 1928 through 1979 water year period (Table B). On the average,

nearly 37 percent of the mean annual flow of the South Platte River occurs

during May and June. Lowest seasonal flows occur most commonly during

August and September. The change in flows at Julesburg since 1952, are

believed to be due primarily to effects of the COlorado-Big Thompson

Project. Mean annual flows of the South Platte River at Julesburg have