FLOOD01776

• County: Pueblo
• Community: Pueblo
• Stream Name: Pueblo Reservoir
• Title: Pueblo Reservoir 1993 Sedimentation Survey
• Date: 5/1/1994
• Prepared For: State of Colorado
• Prepared By: BOR
• Floodplain - Doc Type: Educational/Technical/Reference Information

1993 Resurvey

Fieldwork for the 1993 survey began in the spring of 1993. The hydrographic survey was
completed in late April near reservoir elevation 4859.0. The preliminary field work,
performed by personnel from the Eastern Colorado Projects Office and the Pueblo Reservoir
Operations Office, consisted of locating and flagging the existing sediment range end
markers, relocating the destroyed ones, and surveying the range lines not accessible by boat.
The hydrographic survey was performed using Reclamation's small boat bathymetric survey
system. The small boat system consisted of a sonic depth recorder and a reflector prism
mounted on the boat. The distances from a known point, usually one of the range end
markers, to the small boat were determined as the boat proceeded along the range line by
an EDM (electronic distance measuring) instrument set up on shore and aimed at the
mounted reflector target. Range distances were communicated by radio from the shore to the
boat at preselected intervals and marked on the sonar charts as the boat proceeded across
the reservoir. The boat was held on course as closely as possible by radio communication
from the EDM operator to the survey boat. This system was used to collect the underwater
data for range lines 1 through lOA, 20, 21, 30, 40, 41, 42, 50, and 60. The data for range
lines 11 through 16, 43, 51,61, and 62 were collected by conventional land survey methods.
Data were not collected for range lines 17, 18, and 70 because their location was not affected
by previous reservoir operations.

RESERVOIR AREA AND CAPACITY

Development of 1993 Contour Areas

For the purposes of the sedimentation analysis and to better represent storage changes, the
reservoir was subdivided into segments, using the range lines to delineate the limit of each
segmental boundary. The 1993 reservoir surface areas were computed by the width
adjustment method described by Blanton (1982) and illustrated on figure 5. The method
entails computing the new segmented contour area, A1, between ranges by applying an
adjustment factor to the original segmental contour area, Ao. The computed adjustment
factor for each segment was the ratio of the new average width to the original average width
for the ranges, outlining the segment at the specified contour elevation. The input data
included the original and 1993 range line data along with the segmented areas for the
affected contour elevations. A comparison of simultaneous plots of original and 1993 range
profiles indicated the lateral distribution of sediment at the different measured contour
elevations. Where these plots indicate changes have occurred on the side slopes of the
reservoir, a decision was made to determine whether the change was caused by actual
deposition, erosion, or survey inaccuracies. No area adjustment was made if the measured
change was judged to be caused by survey inaccuracy. The 1993 total reservoir surface area
at a given contour is the original total area minus the summation of all segmental areas
silted in at that elevation. The 1993 total area computation results are listed in column (2)
of table 2.

1993 Revised Storage Capacity

The storage-elevation relationships based on the 1993 underwater survey data were
developed using Reclamation's area-capacity computer program ACAP85 (Reclamation, 1985).
The 1993 surface areas resulting from the width adjustment computations at 5-foot contour
intervals were used as the control parameters for computing reservoir capacity. The program

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