(Map created by E. Carlson, 2008)
Classification of process domains in the Poudre River watershed was envisioned as a way to simplify complex fluvial systems and group streams with similar geomorphic characteristics. Experience in fluvial geomorphology and knowledge of the watershed by contributing members were used to develop a classification of the main channels in the watershed. The entirety of the watershed was classified with segments of channel and surrounding areas described by one of eight classes.
The definition of our main stem rivers was those which drained areas greater than 100 km2. This threshold was chosen through previous field reconnaissance and restricted by the goals of the project. The Big South branch of the Poudre River was compared to similar drainages in other Front Range watersheds and it was determined that a significant shift in process was likely to occur at the 100 km2 mark. One of the goals of the project was to simplify the variability inherent in river systems. Completing the classification at a coarse scale with a minimum mapping unit (MMU) of 1000 meters helped satisfy this goal.
The basic data input used was a digital elevation model (DEM) with a horizontal resolution of 10 meters covering the entire Poudre River watershed, extending past the mountain front. From this data layer calculations of valley slope, hillslope, and valley width were performed to aid in developing the classification. The degree of confinement was used as the primary characteristic with which to categorize the land and streams. Confinement was defined as valley bottom width. The boundary between the valley bottom and the hillslope was defined using flood information from the Front Range to determine a maximum depth of inundation for a flood magnitude of greater than 100 years. A range from three to five meters was obtained and used to assess the width of the valley bottom. Using cross-sections measured remotely in Arc GIS 9.2, we were able to break the spread of width measurements into three classes of confinement. The spread of cross-section widths was combined with knowledge of the river system to develop the width classes.
The maps were created by "hand" meaning that each segment of main stem river (between minor tributary junctions) was examined. The MMU of 1000 m was a logical choice for this type of work. Fluvial processes perform work on a range of spatial scales. The scale the project decided to address was towards the coarser end of spatial resolution. Variability in contiguous river segments that totaled less than 500 m were combined into the dominant process type of the river segments. As the drainage area falls below 100 km2 it was expected that the fluvial processes would begin to act on a different spatial scale than this project was addressing. Therefore much variability could be present in areas classified as Other Processes, but were not addressed in this project. The areas designated Colluvial Processes are present in the uplands sections of the watershed following ridgelines between the channel networks. This process domain could play an important role in influencing other process domains, likely the Confined domains, where hillslope activity could be directly coupled to fluvial processes.
(Map prepared by Chris Sturm, Colorado Water Conservation Board)
Below is a link to the pdf of water supply and storage map compiled by Chris Sturm: