Geomorphic Assessment of Channel Systems
3.1.2 FIELD INVESTIGATION
The purpose of this section is to provide information that will help you conduct a field
investigation of a stream system. General guidance that will help make your field
investigation more effective are given and a list of some of the more common morphological
and sedimentary features that should be noted while in the field are discussed.
A detailed field investigation of the watershed is extremely important in assessing
channel stability because the physical characteristics of the stream are indicators of the
dominant geomorphic processes occurring in the basin. Reconnaissance of the watershed by
helicopter or small plane prior to the more detailed ground investigation is helpful in
determining basin wide characteristics which might otherwise have been overlooked. These
visual observations, coupled with the initial analysis of maps and aerial photos, will help to
identify problem areas, locate key reaches, and to develop a broad understanding of the
general characteristics of the basin so that you can more effectively layout a plan for the
detailed ground investigations. Experience shows that watershed perspective developed from
these broad overviews allows the investigator to assess bank erosion problems within the
context of the wider fluvial system.
Photographs are the cheapest, yet one of the most important products of a field trip.
Photographs of channel instability and other problems, as well as photographs of stable
sections, are invaluable in presenting observations. It is necessary to record the location, date,
and general description of each photo while in the field. Observations made at an unrecorded
location are of little value when making a study of this type. Aerial photographs or recent plan
surveys are easily carried to the field and provide information that is of sufficient detail to
locate key areas or features accurately. When in the field, always keep in mind the maxim that
this may be the only chance you have to view the area, for in many instances, time, funding
or other constraints may prevent you from returning to the field. Therefore, when you go to
the field, it is imperative to obtain complete and accurate field notes and photographic
coverage of the study area for use back in the office.
During the stream reconnaissance, it is important to locate and observe areas where
the problems associated with the particular study are exemplified. This will give you a
perspective into the intensity and spatial distribution of the processes involved. By observing
the areas which have the worst problems, you will be able to establish the upper limits of
erosion, sedimentation, and/or flooding. It is equally important to visit reaches of the system
where these problems are either not as apparent or absent. This will allow you to define a
total envelope of values associated with the study area and to understand the variability of the
physical characteristics of the various reaches in the stream.