|
Summary
Report
CMER/RSAG Temperature Workshop - 2001
Prepared for the Washington Department of Fish and Wildlife
Prepared by: EDAW, Inc.
EXECUTIVE SUMMARY
The purpose of this
report is to summarize the proceedings and discussion from two workshops
on the subject of heat transfer processes in forested stream environments.
The workshops, held in Lacey, WA in February and May of 2001, were organized
as part of the Cooperative, Monitoring, Evaluation, and Research (CMER)
program, and sponsored by the Riparian Scientific Advisory Group (RSAG).
The goals of the Temperature
Workshops were to identify where scientific consensus exists and where
it is lacking on heat transfer processes in forested watersheds,
to provide overviews of past and current research, and to identify future
priorities based on stakeholder review of this information. Specific topics
addressed included:
- The effects of
direct solar radiation to surface waters and the cumulative effects
of heating from upstream sources;
- Currently used
temperature models, addressing their inputs, strengths, and weaknesses;
- Heat transfer processes
via groundwater; and
- Heat transfer processes
via microclimate conditions (both in the riparian zone and over
the stream).
Recognized scientific
leaders in current research efforts were identified and invited as panelists
in the workshops. Invited panelists included Dr. George Ice, NCASI (who
addressed solar radiation inputs); Dennis Schult, Western Watershed Analysts
(who discussed current temperature modeling efforts); Dr. Patricia Olson,
Pacific Watershed Institute (who addressed groundwater inputs); Dr. Sam
Chan, PNW Lab/USFS (who addressed microclimate conditions in riparian
areas); and Dr. Sherri Johnson, OSU (who addressed microclimate effects
on stream systems).
Areas of Consensus
Among Panelists.
Solar Insolation
The panelists noted that the best science to date has confirmed that solar
insolation (i.e., direct solar radiation to the water's surface) is the
dominant source of heat energy to surface water. Although other heat sources
received considerable attention in recent years, validation of these effects
is lacking.
Microclimate
Although older reviews on water temperature frequently refer to microclimate,
successful measurement of this effect on surface water temperature has
been elusive. In the past four years, a number of careful studies have
taken advantage of the availability of reliable low cost submersible data
loggers to isolate the microclimate effect. These data loggers should
be reliable enough to detect differences in water temperature 0.5 centigrade
units or less. These studies (Brosofke et al 2000, Johnson and Jones 2000,
James pers. comm.) have not been able to measure a microclimate effect
on water temperature where there was a buffer 15 meters (50 feet) wide
or greater. Where buffers are narrower or absent, it becomes impossible
to separate the microclimate effect from the more significant solar insolation
effect.
The microclimate hypothesis
suggests water temperatures will always move towards equilibrium with
the surrounding air. Panelists noted that this was still a fundamental
fact. However, elevated air temperature occurs only during the middle
of the day. Air has a significantly lower heat capacity than water, thus
it takes significant time for air to bring a body of water into equilibrium.
Furthermore, microclimate effects from timber harvest are a combination
of three effects; higher mid-day air temperatures, lower mid-day humidity,
and higher wind speeds. The latter two effects combine to increase evaporation
from the water's surface, which has a cooling effect on water temperature.
Solar Tracking
Several panelists suggested that a better measure of solar insolation
would to measure the shade in the path of the summer sun, i.e., solar
tracking, rather than measuring the shade from the entire 'view to sky'.
The current board manual densiometer method assumes the latter.
Groundwater
More research is needed to determine forest practices induced groundwater
effects on surface water temperature. At this time relatively little is
known with certainty.
Headwater Temperature
Transfers
Panelists agreed that surface water temperature in headwater streams
did re-establish temperature equilibrium with air upon re-entering shaded
stream reaches The distance and time that it takes to re-establish equilibrium
is a function of many variables.
Areas of Non-Consensus
There were no major areas of non-consensus among the panelists.
Future
Research Priorities
Solar Insolation
No future research is needed to validate the fundamental effects of
solar insolation.
Solar Insolation
Measurement
Research is needed on the most effective measure of solar insolation.
Current rules require a densiometer, which is time consuming to use and
readings are subjective. In recent years, there have been a number of
additional tools available that appear to be more precise and eliminate
user subjectivity. Research into the utility of these tools for research
measurements and rule implementation would be desirable.
Solar Tracking
Research on this subject as it applies to forest channels is sparse. If
solar tracking proves to be a better predictor of water temperature response,
this would create flexibility to manage for other riparian functions on
the north bank of stream channels. Evaluation of tools for measuring shade
along summer solar pathway is needed. This is a moderate priority for
research.
Headwater Temperature
Transfers
Additional research is needed to validate the distance and/or time
needed to achieve equilibrium with surrounding physical conditions. This
is a moderate priority for research.
Microclimate
In light of recent findings and current riparian buffer requirements,
additional research on the effects of microclimate on water temperature
is a low priority. It may be worthwhile reviewing the scientific literature
in several years. The data logger technology will likely facilitate additional
scientific publications.
Groundwater effects
Research on groundwater is in a very early phase of development. Both
the theory and field methodology need development. A workshop discussion
group identified that need for a conceptual model of heat transfer to
groundwater, and then from groundwater to surface water. The model will
be used to identify priority areas for initial research. This is a high
priority.
Eastern Washington
Nomograph
There was a broad consensus that the eastern Washington nomograph that
is currently in the Board Manual should be revised using current datasets.
If possible, a model that considers more that elevation should be developed.
This is a high priority
Western Washington
Nomograph
With the current 50 foot core zone and an additional inner zone, the western
Washington nomograph is not likely to see much use, and thus, it is a
low priority for research.
Hyporheic Exchange
Initial research by Johnson and Jones 2000 suggests that hyporheic heat
exchange in alluvial streambeds and valley floodplains could have a significant
effect on surface water temperature. It appeared to be considerably more
significant than the microclimate effect. Other studies also suggest this
effect may be under-rated. If significant, the restoration of bedrock
channels that were historically alluvial channels, and the restoration
of incised channels may be legitimate methods for water temperature restoration.
Although this in not a Schedule L-1 question, further research on this
subject may be worth considering.
|
