The goal of this project is to develop and deliver a statewide Geographic Information Systems (GIS) tool that will delineate those portions of the National Hydrography Dataset (NHD) that have been visually determined to be hydrologically modified (i.e., ditches, channelized streams and impoundments). This project is being conducted in support of the Minnesota Pollution Control Agency’s water quality monitoring and assessment program, with support from the Clean Water, Land, and Legacy Amendment.
Specifically, the MPCA is developing a refined stream use designation process
Tiered Aquatic Life Uses (TALU). An accurate statewide determination
of altered stream segments based upon the current NHD linework will assist in
the assignment of the correct beneficial use class for a stream under the TALU
framework. The NHD does not provide an accurate representation of the number of
altered stream miles within Minnesota, therefore this project will utilize
multiple types of information (e.g., LiDAR, aerial imagery, historic aerial
photographs, and observations from on-the-ground surveys) to determine the
extent of stream modifications. This project will provide the first baseline
account of the extent of hydrologic alterations in the state of Minnesota.
Original source of funding is provided by the
Clean Water Fund of the
Clean Water, Land and Legacy
Examples of how data are used to determine hydrologic alteration with a stream:
Figure 1: Aerial photograph from 1938. Red arrows indicate natural bends (sinuosity) in the stream.
Figure 2: 1991 leaf-off aerial imagery. Note that the natural bends from the 1938 aerial photographs no longer are connected to the stream.
Figure 3: LiDAR imagery (hillshade function). LiDAR imagery provides further indication that the natural stream channel has been ditched. Red arrows highlight the remnants of the natural bends. In this figure you are also able to see the dredge piles created as a result of channelization.
In 2008, the Land Management Information Center (now MnGeo) undertook a pilot project to develop a methodology to distinguish between natural and altered watercourses and to create a ‘natural/altered watercourse’ tool tied to the high-resolution NHD. The pilot project evaluated portions of several 8-digit HUC watersheds in different parts of the state in order to create a methodology that would work under the full range of hydrologic regimes found throughout Minnesota. During the pilot effort, areas were chosen in the North Fork Crow River (07010204), Snake River (St. Croix Basin - 07030004), and Redwood River (07020006) watersheds. (Click on thumbnail to view a larger version of this map). The method development effort included review of results by MPCA staff and quality control against site information assembled by MPCA.
The statewide project will build upon the efforts completed in the 2008 project and will refine the methodology, create new tools to aid in data processing, add additional layers (e.g., LiDAR and 2009-2011 aerial imagery), and complete a comprehensive visual analysis of all streams statewide.
Phase I (orange) – This phase encompasses 27,467 square miles with a majority of watersheds representing the Red River basin; however three watersheds (Minnesota River-Yellow Medicine, Mississippi River-Twin Cities, and Mississippi River-Winona) were also added to this delineation schedule. These three watersheds were added because the MPCA will perform water quality assessments on these watersheds in the coming year, therefore having these data available during assessments will allow for further understanding of habitat modifications within a particular watershed. This phase is scheduled for completion spring-summer 2012.
Phase II (blue) – This phase encompasses 32,119 square miles with watersheds representing the Minnesota River, Lower Mississippi River, and Central Lakes basins. This portion is scheduled for completion by summer-fall 2012.
Phase III (green) – This phase covers 24,781 square miles representing watersheds within the Arrowhead and Central Lakes Basin. This portion is scheduled to be completed fall 2012-spring 2013.