FLOOD00457

• County: El Paso
• Community: Colorado Springs and Manitou Springs
• Title: Paleohydrologic Flood Investigations for Streams in Manitou Springs and Colorado Springs
• Date: 12/3/1987
• Floodplain - Doc Type: Flood Documentation Report

were noted to determine the approximate age 01 the tree and deposit).
As a general guide in this study, trees that had been cut (within
about the last month) along the Pikes Peak railroad right-01-way along
Ruxton Creek were used to estimate tree diameter and age relations 10r
several spruce (believed to be Englemann spruce) trees. For example,
a 2-inch spruce had 10 annual growth rings, a 4-inch spruce had 35
annual growth rings, and, a 15-inch spruce had 70 annual growth rings.
These can be used to estimate the relative age 01 spruce trees on the
1100d deposits (roughly, 1 inch 01 diameter represents 5 years 01
growth), hence, an approximate time since the deposits were 10rmed.
In mountain channels not subject to signi1icantly out 01 bank
110ws, channel conditions are much di11erent. These channels
generally show very little evidence 01 sediment movement and channel
erosion or depositional 1eatures. Bed material show no evidence
signi1icant movement, channel banks are well vegetated with grass and
moss (Figure 2B). Boulders and bedrock just above the water level
generally are covered extensively with moss and lichen indicating that
flood waters have not disturbed the channel 10r a long time.
Vegetation, even those growing immediately next to the channel do not
show any, or only minimal, evidence 01 scarring 1rom 1100d debris.
There is no vegetative 1100d debris lodged upstream 1rom obstructions.
The height 01 the 1100d deposits and scarred trees provide an
indication 01 the approximate flood depth; widths can be measured in
the channel at these sites and to then estimate mean 1100d depth.
From these, approximate cress-sectional area can be estimated. Then
methods can be use to estimate velocity (extensive work has shown that
a reasonable mean 1100d velocity in these mountain channels is 10 1eet
per second and was used 10r this investigations) and peak discharge.
A mean velocity of 10 1eet per second is conservative (overestimated)
10r recent 110ws.
Onsite investigations to locate 1100d erosional and depositional
1eatures were conducted in Ruxton Creek (the stream considered to have
the greatest 1100d hazard), Williams Canyon, Fountain Creek (and
tributaries upstream 1rom Manitou Springs), Sutherland Creek, and Camp
Creek (Figure 1). For the paleo1100d investigations in this study,
channels were inspected to indenti1Y erosional and depositional
1eatures (indicators) 01 out of bank 1100ding. Use 01 the
paleohydrologicj techniques described above has allowed 10r the
estimation 01 3 general level 01 1100ds, recent (or 1requent), in the
last 10 years, medium, in the last 30 to 100 years, and, the maximum
flood, greater than 100 years. These onsite investigations are
representative 01 110w conditions for a reach of channel. These
observations are discussed below for each creek, starting with the
most downstream basin. Estimates 01 width, depth, discharge, and
approximate time since a 1100d 10r recent, medium, and the largest
observable 1100d are shown 10r the sites investigated on Figure 1.
These investigations were only made in natural stream channels
upstream from urban development because this development disturbs the
1100d deposits. Time was not available to visit other tributaries,
such as Cheyenne and Bear Creeks, but these investigations are
believed to provide an understanding 01 the local 1100d hydrology.

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