Geoscience Reference
In-Depth Information
7.3.1 Preliminary Evaluation of GIS-Based Mapping
The initial GIS mapping was reviewed to determine how it could be utilized
to select areas for possible wetlands and/or stream restoration/enhancement sites.
Four general restoration categories were developed based on this evaluation:
1. Stream Restoration/Enhancement Sites - This designation included stream
segments that were found to be in the “restorable warmwater” habitat quality
range, i.e. having a Qualitative Habitat Evaluation Index (QHEI)
45-60, with
a very narrow 100-year floodplain - indicative of channelization or natural incision
- and very little forest cover within 200 ft of the channel (for more background on
QHEI scoring the reader is referred to OEPA (
1989
) and Rankin (
2006
)).
2. Wetland Restoration/Enhancement Sites - This category was developed to identify
hydrologically isolated, generally topographically flat hydric areas containing hydric
soils that were currently farmed or were recently abandoned agricultural fields.
3. Streams with Adjacent Wetlands - This category was developed to identify those
streams in the 'restorable warmwater' habitat quality range (QHEI
¼
45-60),
with a wider 100-year floodplain (indicating minimal channelization or natural
incision), the presence of topographically flat hydric soils or nonhydric soils with
hydric inclusions, and very little forest cover within 500 ft of the stream channel.
These areas were considered to be prime candidates for non-isolated, floodplain
wetland restoration where, once restored, the wetlands habitat would have the
potential to positively impact BUI's through shading, sediment deposition and
filtering, reducing erosion, and increasing and extending baseflow. There may also
be some in-channel work associated with this category.
4. Urban Restoration/Enhancement Areas - In addition to the above categories, the
project team also considered an urban restoration/enhancement restoration/cate-
gory, where there are floodplain encroachments and impervious surfaces limit-
ing lateral expansion of the stream cross section. Here, the only option in urban
situations might be multi-stage channel construction to restore some channel
morphology and increase bank stability.
¼
The GIS mapping was refined to ensure that the data obtained from the various
sources would be useful in developing a predictive model that would identify sites
that fell within the four categories listed above with varying degrees of restoration/
enhancement potential. The most currently available aerial base mapping was also
added to the GIS mapping, so that existing land use could be better assessed before
going into the field for data verification. The result was a preliminary map based on
ranking the potential restoration sites from high to low (Fig.
7.3
).
7.3.2
Initial Field Verification of GIS Mapping
The preliminary ranking map was then examined in order to further identify the best
areas for restoration opportunities. Forty potential wetland and/or stream restora-
tion/enhancement sites were then selected from the preliminary GIS data analysis
