FLOOD04263

• County: Statewide
• Basin: Statewide
• Title: Design of Open Channels
• Date: 10/1/1977
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Educational/Technical/Reference Information

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CHAPTER 3. SITE INVESTIGATIONS

Introduction

Methods of investigation and testing of soil conditions along a channel
system ate discussed in this chapter. The purposes of these investiga-
tions and testing are to evaluate the resistance of the soils in the
bed and banks of the channel to erosion forces, to evaluate the sediment
transport relationships, to determine slope stability against sloughing
and sliding, to estimate earth loads that may act on structural members,
and to determine the rate of water movement through the soils.

The procedures include identification, sampling, and testing or evalua-
tion of stratigraphic units encountered in the channel system to be
modified and an evaluation of the sediment transport characteristics
of the system.

Investi~ation Requirements

There are conditions specific to investigations for channel improve-
ments that cause them to differ from investigations at other types of
construction sites. One usually significant difference is that channels
may extend for many miles through a variety of materials. This fact
demands that data obtained from anyone test hole must be correlated
on as knowledgeable a basis as possible with data obtained at the next
test hole, both upstream and downstream. A distinguishing feature of
investigations for channel improvements is that almost always they are
located in alluvial material. The stability of channels is affected
by watershed conditions upstream that control the availability of bed
material, and by ground""Water conditions at the site. A similarity
with foundation investigations for other structure sites exists in
that the in-place characteristics of the soil materials are very
important if these characteristics that pertain to erodibility differ
from those that exist when the material is disturbed.

The following sequence of work is needed to appropriately recognize the
conditions specific to investigations for channel improvements while
ensuring that an adequate amount and type of data are obtained.

1. Determine the geomorphology of the deposits in which the channel
is to be located to the limit necessary for this purpose.

2. Identify stratigraphic units along the proposed channel route
and to a depth of at least three feet below the invert or channel
bottom elevation as proposed. A stratigraphic unit is defined in
this instance as an identifiable stratum of alluvium or other soil
material whose susceptibility to erosion is a reflection of the
original materials, mode of accumulation and the changes that have
occurred since deposition or soil formation.