WSP06041

• File Number: 8210.470
• Description: Pacific Southwest Interagency Committee
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 10/1/1968
• Author: Unknown
• Title: Report of the Water Management Technical Subcommittee - Factors Affecting Sediment Yield and Measures for the Reduction of Erosion and Sediment Yield - October 1968
• Water Supply Pro - Doc Type: Report/Study

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Reservoirs - To provide for permanent storage of sediment and either tem-
por~ry or permanent water storage.

Revetments - Materials placed on the stream bank to protect it from erosion
by stream flow.

Sills - Structures of rock, masonry, rails, etc., placed at channel grade
to prevent stream'downcutting.

Disturbed Area Protection - This measure may include any of the above treat-
men~s and structures. In addition, it often includes stabilizing steep
slopes, lining road ditches, etc.

Applicability of Management and Land Treatment Measures for Erosion and
Sediment Control

The soils, climate, topographic and other factors which tend to create the
most severe erosion and sediment problems also increase the difficulty of
control. Similarly, many measures are usually more successful under con-
ditions of low or moderate erosion and -sediment yield than they are under
hig~ yield. The broad trends in the principal factors affecting erosion
indicate the reasons for this. Vegetative measures are dependent on favor-
abl~ moisture conditions and proper grazing control. Although there are some
notable exceptions in the Pacific Southwest, the more humid sections usually
show less sediment yield than more arid sections, as more favorable moisture
furnishes greater support to vegetation. Similarly, the mechanical treat-
ment measures which require disturbing, molding, or reshaping the soil are
mos:t successful where the soils have p~operties which inherently make them
res:istant to erosion. The other factors operate in much the same way and
in 'an interdependent fashion. As the slope increases, for instance, problems
of 'establishing and maintaining vegetation, applying mechanical treatment
and obtaining proper grazing use also increase.

Figure 1 shows the climatic environments of the Pacific Southwest. The indi-
cated large variations are most pronounced in the mountains and valleys of
the region where the mountain peaks may be humid and the valley bottoms arid.
This variation causes many planning problems.

Th~ measures that are used for erosion and sediment control in the Pacific
So~thwest may be classified by purpose into several groups: (1) to inter-
cept and/or conserve moisture; (2) to increase infiltration capacity; (3)
to reduce or eliminate stress on existing cover; (4) to preserve existing
coYer regarded as adequate or in the process of becoming adequate with time;
(5) to increase the protection of the soil by a change in the type as well
as density of vegetation.