FLOOD10157

• Designation Number: 74
• County: Arapahoe
• Community: Aurora
• Stream Name: Granby and Sable Ditches
• Basin: South Platte
• Title: FHAD - Granby and Sable Ditches, Aurora, Colorado
• Date: 4/1/1977
• Designation Date: 7/27/1977
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
I
I
I
I
I
.
I
I
I
I
I
I
I
I

-5-

Probability Profiles for Sable Ditch and Granby Ditch
are provided in Figures 7 and 8 respectively. These charts
related the peak discharge at any point within the basin for
the 10-, 50- and 100-year storm frequencies. Table V lists the
flood frequencies and discharges at selected design points.

No detention was considered upstream from East Sixth Avenue
or the Highline Canal in the development of the flood
hydrology for Granby Ditch.

Varying rainfall intensities were assumed to occur in each
basin. Table III lists the maximum rainfall depths for the
10- and 100-year storm frequency for a 2-hour duration storm.
An infiltration rate of 0'.5 inches per hour was utilized in
all of the study basins. The runoff computations included
considerations of the percentage of watersheds developed and
planned future development, as determined by field reconnaissance
and information from the City of Aurora.

Typical flood hydrographs for the two ditches are provided
in Figures 1 through 6 in the Appendix of this report. Discharge

Table V
Design Point Peak Discharges

Table IV
Basin Parameters Drainage Area mi. 2 Design Point
Projected Granby Ditch
Upstream limit of study
Area Basin Length Centroid Slope Perv. Development 1. 38
Basin (sq. mi.) ~,mi.) Length (mi.) % % CP CT (Laredo Street)
1.96 Colfax Avenue
Granby Ditch Confluence with Sable
1.38
G-l .32 .80 .61 .83 34 .51 .30 Ditch (Granby Ditch only)
.36 Sable Ditch
G-2 .58 1. 36 .76 .92 49 .52
1.02 Colfax Avenue
G-3 1. 38 2.65 1. 32 .92 70 .68 .55
1. 46" Confluence with Granby
Sable Ditch Ditch (Sable Ditch only)
1. 06 40 .56 .03 Granby and Sable Ditch
S-l .45 1. 48 .99 (Below Confluence)
S-2 1. 02 1. 52 .68 .99 65 .64 .49
3.74 Confluence with Granby and
Sable Ditch (both basins)

f,

- 64._"
l f - _
Tj"

Cr;( 0

I/, ,,~ ,

'"" -', ~
- "

".

- 'L I \L').3-
'- t'" ( c:::..., " j

" ,-;
''''

('\ rt

I '3& ~ .
\,':,
.q
" >,
-;;. i_~ 't ~v ":'.'L ,"""I

\ ,.<'

"

i-'

'1,,:::'

o ~...,

?" '

Fully
Developed Conditions
Discharge
10-year 100-year

675 cfs 1085 cfs
880 cfs 1380 cfs
935 cfs 1445 cfs
.
730 cfs 1130 cfs
910 cfs 1405 cfs

1800 cfs 2775 cfs