Stream Geomorphic Assessment Process

The SGA process is broken down into three phases:

  • Phase  I, this is the remote sensing phase in which large areas can relatively quickly be assessed from maps and aerial photography.
  • Phase II, in this phase data is collected in rapid field assessments at the reach scale. In this phase the geomorphic condition, adjustment processes, reach sensitivity, and stage of channel evolution are categorized. Phase II data was used to make the maps in this project.
  • Phase III, in this survey level field assessment usually completed for sites of proposed restoration projects. Phase III surveys can take several days to assess one river reach.

Below are detailed descriptions from the Rivers Program about the process of data collection involved in each phase of the SGAs. You can read more about the SGA process here

Phase 1:

The remote sensing phase, involves the collection of data from topographic maps and aerial photographs, from existing studies, and from very limited field studies, called “windshield surveys.”  Geomorphic reaches and provisional reference stream types are established based on valley land forms and their geology. Predictions of channel condition (departure from reference), adjustment process, and reach sensitivity are based on evaluations of watershed and river corridor land use and channel and flood plain modifications.  While stream types and adjustment process predictions are provisional, the Phase 1 remote sensing techniques allow for a large watersheds (100-150 square miles) to be assessed within a few months time.  GIS and database tools have been developed to automate many Phase 1 measurements and to aid in data evaluation.  Computer and river assessment skills are necessary but there are plenty of tasks that can be completed by someone with limited training.   Because the Phase 1 database is developed and may be continually refined for an entire watershed, it can be referred to over-and-over again when issues arise at the reach scale for which river form and processes need to be understood in a watershed context.  The Phase 1 assessment is ideal for flagging reaches and completing field studies that will address the goals and issues defined by the assessment group.  If you are working on a small watershed (less than 5 square miles), and have already decided  to complete extensive field surveys throughout, you may decide to go directly to the field  (Phase 2 and/or Phase 3) and return to the Phase 1 assessment to record reference conditions and complete impact ratings.

Phase 2:

The rapid field assessment phase, involves the collection of field data from measurements and observations at the reach or sub-reach (segment) scale.  Existing stream types are established based on channel and flood plain cross-section and stream substrate measurements.  Stream geomorphic condition, physical habitat condition, adjustment processes, reach sensitivity, and stage of channel evolution are based on a qualitative field evaluation of erosion and depositional processes, changes in channel and flood plain geometry, and riparian land use/land cover.  Phase 2 assessments are described as rapid but can take 1 to 2 days in the field to complete for a one mile reach, depending on how many different conditions or sub-reaches are encountered.  Database tools have been developed to facilitate Phase 2 data reduction and reporting.  Stream geomorphic and habitat assessment skills are necessary, but there are plenty of tasks that can be completed or assisted by someone with limited training.  Over one or two field seasons, enough Phase 2 work can be completed in the field to enhance watershed assessment with a “like reach” analysis of the Phase 1 database.  The Phase 2 assessment is ideal for flagging reaches for protection and restoration projects and the completion of Phase 3 assessments.

Phase 3:

The survey-level field assessment phase, involves the collection of detailed field measurements at the sub-reach or river site scale.   Existing stream types and adjustment processes are further detailed and confirmed based on quantitative measurements of channel dimension, pattern, profile, and sediments.   Phase 3 assessments are completed with field survey and other accurate measuring devices and can take 3 to four days to survey a sub-reach of two meander wavelengths.  Spreadsheet and data base tools have been developed to facilitate Phase 3 data reduction and reporting.  Professional level stream survey and geomorphic assessment skills are necessary.  Phase 3 assessments are typically pursued to augment data requirements for the design and implementation of river corridor protection or restoration projects.  The ANR also uses Phase 3 assessment protocols to develop reference tools (such as regional hydraulic geometry curves) for Phase 1 and Phase 2 assessments.

Stream Geomorphic Assessment Data Viewer:

You can see a map of all of the SGA data for Vermont through the: Stream Geomorphic Assessment Viewer