WSP06144

• File Number: 8210.470
• Description: Organizations - Pacific Southwest Inter-Agency Committee - PSIAC
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 10/1/1968
• Author: PSIAC
• Title: Pacific Southwest Inter-Agency Committee - Report of the Water Management Subcommittee
• Water Supply Pro - Doc Type: Report/Study

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13

of this appendix. The new rating sheet is a modification of the
N PSIAC sediment yield rating, sheets prepared by the 'Department of
00 Interior, Bureau of Land Management. The modifications would
tQ reflect the changes proposed in the above 15 modifications. These
oo,J sheets would be used in the field for ratings and docUlIientation of
the rating factor data. It is proposed that these two sheets be,
published or issued to field personnel in a front-to-back printing
mode. In practical use, completed rating sheets could be used in ,
reports as data documentation of field sediment yield evaluations.
It is urged that a maximum amount of notation be made on these
sheets in the field to record the development of the rating
process.

Modification 17: It is proposed that the PSIAC sediment yield
graph on the back of the BLM PSIAC rating sheet be replaced by a
PSIAC sediment yield chart that eliminates the field plotting of
sediment yield from a 2-10g graph. A chart of a direct sediment
yield values for PSIAC ratings ranging from 1 to 135 is included in
the Revised PSIACRating Sheet. The chart was developed from
Renard (1980, p. 167) and BLM graphic plot of PSIAC. The equation
used to developed the chart is: '
K aC-ft/mi sq = antilog [(0.015656 x PSIAC rating)- 1.085666)

It is further recommended that the sediment yield conversion graph
(aLM) be included in the text portion of the PSIAC procedure.

THE REVISED PSIAC PROCEDURE AS USED IN THE COLORADO RANGELAND
SALINITY CONTROL PROJECT

The above proposed modifications to the PSIAC procedure were
implemented in the Colorado River Basin rangeland salinity control
project.

Watersheds Were divided into geomorphic units. A PSIAC sediment
yield rating was modelled. for each of the geomorphic units that
reflected the Present condition of the unit. The .PSIAC procedure
was then used to model a Future without Project (FWOP) condition
and a Future with Project (FWP) condition.

The Present condition was modelled through direct field observation
by an interdisciplinary team. Each PSIAC factor was rated by a,
specialist for that factor or by use of technical data.

The rating factors (a) Surface Geology, (b) Soils, (c) Climate and
(e) Topography are constant within a geomorphic unit for the future
condition models (FWOP and FWP).

The FWOP condition is the extension of Present condition trends
into the future for a number of years relating to the life of land
treatment planning measures. Factor ratings can be increased,
decreased or remain the same by continuation of current land

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