WSP09636

• File Number: 8149.911
• Description: Miscellaneous Small Projects and Project Studies - SE Needs Assessment and PSOP
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 11/12/1997
• Author: Frank Kipple
• Title: Changes in Arkansas River 1963 - 1997
• Water Supply Pro - Doc Type: Report/Study

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TO:

Steve Witte

FROM:

Frank KippleC l\:v.2. \

DATE:

November 12, 1997

SUBJECT:

Arkansas River at La Junta, Colorado

CHANGES IN ARKANSAS RIVER CHANNEL, 1963 - 1997

This is in response to a request to look at Arkansas River channel changes at the La Junta gaging station
and highway bridge. The period includes the 1965 flood and the beginning of storage at Pueblo Reservoir.

The fIrst table (Table No. I) of this memo shows the gage height of the point of zero flow for seven of the
ratings from 1963 to the present. The point of zero flow was obtained for 7 ratings (Nos. 30 - 32, 34 - 37)
from either the rating tables or rating curve extension. It also indicates the change in the point of zero flow
compared to that on October 1,1963. The flood of 1965 lowered the point of zero nearly a half foot, but it
has raised a coupie oi feet since- mal time.

Table No.2 compares gage heights of the seven rating tables for 5 selected discharges ranging from 20 cfs
to 10,000 cfs. The data for 20 cfs. has trends similar 10 those for the point of zero flow. The channel
scoured in 1965 then gradually aggraded from 1965 to present. The channel is about I y, foot higher than
in 1963. At the high end of the ratings, the gage height was about 5 feet higher in 1991, compared to 1963
for 10,000 cfs. The earlier ratings, 30 -32, 34, and 35 did not show much change at their upper ends. This
could have been caused by an insuffIcient number of discharge measurements to derme the high end of
some ratings. The 1965 flood probably changed the entire stage-discharge relationship, rather than just the
lower end.

TABLE NO. I
Point of Zero Flow (PZF) Comparison for Selected Rating Tables

Rating Table No. I Period Covered by Point of Zero Flow (PZF) in feet Change of PZF from Rating #30
Rating (gage datum) (in feet)
30 10-1-63 to 9-30-64 3.30 0.00
31 10-1-64 to 6- t4-65 3.50 +.20
32 6-14-65 to 9-30-65 3.00 -.30
34 11-1-67 to 9-30-71 2.88 -.42
35 10-1-71 to 9-30-80 3.28 -.02
36 10-1-80 to 2-28-91 4.06 +.76
37 3-1-91 to present 4.75 +1.45

TABLE NO.2
Comparison of Gage Heights for Different Ratings at Several Discharges

Rating Period Covered Discharge 20 Discharge 80 Discharge Discharge - Discharge
Table by Rating cfs. cfs. 500 cfs. 2000 cfs 10,000 cf.
No. Gage ~ Gage ~ Gage ~ Gage ~ Gage ~
Height gh Height gh Height gh Height gh Height gh
30 10-1-63 to 9-30-64 3.61 0 4.00 0 4.83 0 6.14 0 8.86 0
31 10-1-64 to 6-14-65 3.81 +.20 4.10 +.10 4.80 -.03 6.14 0 8.86 0
32 6-14-65 to 9-30-65 3.26 -.35 3.65 -.35 4.67 -.16 6.14 0 8.86 0
34 11-1-67 to 9-30-71 3.27 -.34 3.92 -.08 5.02 +.19 6.23 +.09 8.86 0
35 10-1-71 to 9-30-80 4.08 +.47 4.46 +.46 5.32 +.99 6.46 +.32 8.96 +.10
36 10-1-80 to 2-28-91 4.52 +.91 4.84 +.84 5.80 +.97 7.08 +.94 9.71 +.85
37 3-1-1991 to present 5.04 1.43 5.42 + 1.42 6.58 +1.75 8.61 +2.47 13.8 +4.94