SI-4A (3/9/05 version)
Watershed-Based Options To Address Stream Integrity Impairment: Watershed-Wide Assessments
As noted in the overview, once a stream integrity problem is identified, steps 1 and 2 in recommending potential solutions are to evaluate the stream system at the watershed-wide scale. During this step of the evaluation process, data about indicators of channel evolution and the impacts of the channel on biology are collected. Channel evolution data is used to determine whether the stream is physically "stable" or "unstable", and if the existing conditions are likely to continue. Biological data is used to determine whether water quality is in attainment with water quality standards, and if not, answer the question, "what are the key causes of nonattainment".
Details about key indicators of water quality attainment are available at the following links:
Details about key indicators of stream stability/instability are available by clicking here. Both qualitative and quantitative stream morphology data collection methods are available as outlined below. Selection of the data collection method will be dependent on the goal of the assessment, ranging from qualitative general knowledge of important stream morphology issues in the watershed to quantitative classification of the type of stream channel most common to the watershed.
- Inventory General Conditions and Issues
A practical assessment exercise may be driving a watershed with topography maps and stopping at convenient points to qualitatively determine the basic channel condition. This can realistically be done for all channels within the drainage network by spot-checking these sites in the field, in combination with existing data on current and historical maps and photos. The desired outcome from this type of assessment is general descriptions of the magnitude and locations of channelized and entrenched areas, stream sinuosity, bank heights, threats to stream stability, and degree of recovery in areas that are evolving toward stability.
- Floodprone Area Mapping
In many areas of the state, floodplain maps are available to show the elevations that will be inundated during a 100-year flood. In contrast, the flood-prone area is defined by the flood stage at two times the channel depth. Mapped information about the elevations of more frequent floods, such as those with a 2-year and 5 year recurrence interval (RI) is more indicative of stream quality, riparian quality and channel morphology over time. GIS based mapping can show the extent of floodplain inundated by flows 1, 1.25, 1.5, 1.75 and 2 times the channel depth.
- Channel Classification
Streams can be classified1 into discrete types based on defining morphological characteristics, using methods such as a Rosgen Level I classification or identification of channel evolution stage. These assessments can be used to predict the most likely source of sediment contribution (instream versus upland), where passive recovery of stream stability has occurred, and to what degree; where, and what kind of direct intervention is advised.
1 "Chapter 3, Rosgen Stream-Classification System/Channel Assessment and Validation Procedures" in the following pdf http://www.bae.ncsu.edu/programs/extension/wqg/sri/stream_rest_guidebook/sr_guidebook.pdf
- Channel Form Assessment Methods