BOARD02035

• Board Meeting Date: 5/16/2006
• Description: ISF Section - Arkansas River Instream Flow Appropriation
• Board Meetings - Doc Type: Memo

"

,.

~~~~ .
The DOW, in September of 2005 and March of 2006, collected stream cross section information,
natural environment data, and other data needed to evaluate the 100 cfs instream flow
recommendation proposed and supported by CWCB staff, the City of Pueblo and other local
water users. The stream cross section data was analyzed using the R2CROSS program. The
R2CROSS output was evaluated using the methods described in Nehring (1979) and Espegren
(1996). DOW collected physical data at four different cross-section locations at three different
discharges (see attached map). The observed flows ranged from a high of 260 cfs to a low of 58
cfs. The width of the Arkansas River at the four study sites ranged from 160 feet to 132 feet.

Cross-Section Locations
Data relating to the individual cross-sections are discussed below:

. Site #1 is located approximately Y. mile downstream of Pueblo Reservoir. The bank full
width of this cross-section was 151 ft and had a hydraulic slope of less than I %. Data
collection flows at this site included flows of 58, 89, 155 and 260 cfs,
. Site #2 is located near the eastern end of Pueblo Reservoir. The bank full width of this
cross-section was 132 ft and had a hydraulic slope ofless than I %. Data collection flows
at this site included flows of92, 155, 178 and 264 cfs.
. Site #3 is located approximately 100 yards down-stream of the railroad bridge crossing
the Arkansas River near Reservoir Road. The bank full width of this cross-section was
160 ft and had a hydraulic slope of less than 1 %. Data collection flows at this site
included flows of85, 155, 174 and 252 cfs. .
. Site #4 is located approximately Y. mile upstream of the confluence with Fountain Creek.
The bank full width of this cross-section was 141 ft and had a hydraulic slope ofless than
I %, Data collection flows at this site included flows of 82, 136 and 223 cfs.

Table 1: Stream F ow Hvdraulics and Channe Charactenstlcs at 100 cfs
Cross-section % Wetted Average Depth Average Velocity
Perimeter
#1 - Below Reservoir 69.8% 0,89 feet 1.06 ft/s
#2 - Lower State Park 72.0% 0.76 feet 1.33 ft/s
#3 - Below RR-Xing 75.9% 0.53 feet 1.54 ft/s
#4 - Above Fountain Ck 61.3% 0.53 feet 2.19 ft/s

I

d

I

A 100 cfs instream flow would provide:

. Enough water to wet approximately 70% ofthe stream channel at 3 of the four x-section
locations and 61 % of the stream channel at cross-section #4;
. An average depth of close to 0.5 feet at all four cross-sections and nearly 0.9 feet at
cross-section # I; and
. An average velocity of over 1,0 feet per second at all cross-sections.

.

8