- CMZ Development
- River Corridor Management
- Corridor Hazard Assessment
Channel Migration Zone (CMZ) mapping is based on the understanding that rivers are dynamic and move laterally across their floodplains through time. As such, over a given time period, rivers occupy a corridor area whose width is dependent on rates of channel shift. The processes associated with channel movement include lateral channel migration, channel avulsion and mass failure of the channel margins. The fundamental goal of CMZ mapping is to identify the corridor area that stream channel or series of stream channels can be expected to occupy over a given timeframe.
Rapp and Abbe (2003) discuss the key concepts for CMZ mapping in A Framework for Delineating Channel Migration Zones. While this document defines many of the key concepts that form the foundation for current CMZ mapping efforts, more recent work by the Washington Department of Ecology and others addresses the variations in approaches that can stem from this foundation. The approaches can vary significantly depending on the available data, scale of analysis and level of effort defined for a project (http://www.ecy.wa.gov/programs/sea/sma/cma/index.html). In Washington State, for example, numerous Channel Migration Zone maps have been developed that reflect a wide variety of methodologies, even though all were fundamentally based on the concepts developed by Rapp and Abbe.
Additional work that we have completed in Montana on the Clark Fork (AGI/DTM, 2009), Yellowstone (DTM/AGI, 2009) and Big Hole Rivers (DTM/AGI, 2005) utilizes the foundations of the original Rapp and Abbe work, while adapting the methods to meet the specific data, geomorphic processes and goals of the project.
Our CMZ Background
DTM has been working with Applied Geomporphology, Inc. (AGI) since 2003 on a broad range of natural resource management efforts. Starting in 2006, DTM and AGI have teamed to create Channel Migration Zones on over 750 miles of Montana rivers, covering a wide spectrum of geologic, geomorphic, hydrologic, hydraulic and land use conditions. In the process, we have developed an approach that engages the client to assist us in making the critical decisions necessary in a CMZ study. We rely extensively on Geographic Information Systems (GIS) to streamline the process of CMZ mapping, and have developed a suite of custom tools, data formats and analysis strategies that allow us to explore multiple CMZ scenarios before settling on final CMZ boundaries.
Completed CMZ Projects
- Prickly Pear/Tenmile Creek, Montana. Lewis and Clark County. DTM and AGI partnered to develop a CMZ for portions of both Prickly Pear Creek and Tenmile Creek in the Helena Valley. A total distance of 18.2 miles was mapped. Working with a Technical Advisory Committee, DTM and AGI mapped and measured the migration rates of these streams between 1955 and 2008. Both creeks are relatively small in size and are flowing over the surface of an alluvial fan. They are also highly modified streams, with many sections confined by bank protection. Using the same techniques previously applied to larger rivers, DTM and AGI developed a CMZ that accurately quantifies channel movement rates for these small streams. Deliverables included a tiled CMZ map, technical memo containing mapping criteria and usage recommendations, and all GIS data associated with the project. We also created an inundation model to help identify areas of avulsion hazard across the alluvial fan.
- Ruby River, Montana. Ruby Valley Conservation District. This project developed a CMZ for 54 miles of the Ruby River, from Ruby Reservoir to the Jefferson River confluence. The study area is characterized by a highly sinuous channel, with many bendways and cutoffs. The channel course is not heavily influenced by bedrock geology, which gives it a classic alluvial geomorphology along its length. The Ruby also tends to have areas of higher avulsion potential. These characteristics resulted in an exceptionally large migration vector dataset, with some areas of extreme migration seen between the study years of 1955 to 2009.
- Flathead River, Montana. Flathead Lakers. DTM and AGI developed a CMZ for 24 miles of the lower Flathead River in Northwest Montana. The study reach empties into Flathead Lake, which is dam-controlled. The lake stand is adjusted seasonally and creates backwater conditions in the lower part of the river. This hydrologic condition drives erosion processes that are separate from channel migration and complicates the traditional method of CMZ mapping. Our CMZ report and map summarizes the effect of these factors on natural channel migration and also evaluates avulsion hazards using an inundation model.
- Clark Fork River, Montana. A Channel Migration Zone map and associated report was completed for approximately 20 miles of the Clark Fork River from the Bitterroot River confluence, downstream to the Six Mile Creek confluence near Huson (AGI/DTM, 2009). For this project AGI and DTM worked closely with members of a Technical Advisory Group assembled by the project sponsor to develop the mapping criteria, as well as review and revise the project maps. We utilized historic imagery that was orthorectified by Mapcon Mapping, Inc., along with more recent imagery available from NRIS. This section of river is defined by four distinct reaches, representing highly-variable channel processes. Understanding these processes was critical for developing an acceptable CMZ map. Deliverables included a tiled CMZ map, technical memo containing mapping criteria and discussions, and all GIS data associated with the project.
- Yellowstone River, Montana. Yellowstone River Conservation District Council. This effort resulted in the development of a Channel Migration Zone (CMZ) map for the portion of the Yellowstone River that extends from the Gardiner, near Yellowstone National Park, to its confluence with the Missouri River in McKenzie County, North Dakota, a distance of approximately 564 miles (DTM/AGI, 2009). This mapping is just one part of a multi-year, multi-agency and multi-discipline cumulative effects study, and it supports the Yellowstone River Conservation District Council in their efforts to develop best management practices for the river. DTM and AGI have been involved with this effort for over six years. Our contributions to the project include: developing geomorphic parameters and associated GIS data (AGI/DTM, 2004); imagery research, acquisition, georeferencing and mosaicking of two suites of historic imagery for the entire corridor; physical features mapping (DTM/AGI 2008); inundation modeling from LiDAR and other DEM sources (AGI/DTM, 2004); along with numerous other tasks. Deliverables for the Yellowstone CMZ project included a series of 10 tiled county-level maps, a detailed report, and all GIS data associated with the mapping effort.
- Big Hole River, Montana. Big Hole Watershed Committee. A primary goal of this project was to produce approximate 100-year floodplain maps and Channel Migration Zone maps for 160 miles of the main stem of the Big Hole River (DTM/AGI, 2005). DTM and AGI worked to identify, scan and georeference two suites of historic imagery; perform a reach-based geomorphic analysis; develop an approximate 100-year floodplain based on inundation modeling; and develop CMZ maps for the river corridor. This was part of a locally led, four-county effort to coordinate land use planning in the Big Hole Basin. The resulting CMZ maps are incorporated into a four-county ordinance for managing the Big Hole River corridor.