Meitzen_TNC summaryJuly162013_for distribution

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Decision Support System for Environmental Flows
Presented by Dr. Kimberly M. Meitzen on behalf of Duke University and
The North Carolina Chapter of the Nature Conservancy

We applied knowledge from literature reviews and independent research supported by TNC North Carolina and Duke University to develop a set of criteria that could be used to determine environmental flows. We developed environmental flow guidelines designed to:
1.) Protect natural flow variability among seasons, ecoregions, and by river basins:
• Allocate a daily amount of net water use calculated from a percent of the monthly median
flow: o 10% of monthly median flow in normal and wet years
o 5% of monthly median flow in drought years

2.) Prevent further water use related impacts to the 10th percentile low flow conditions:
• Require a minimum pass-by flow when flows decrease below a certain percent of the
monthly median flow:
o 60% of the median January – April (50% in drought years)
o 50% of the median May – December (40% in drought years)
3.) Protect headwaters statewide:
• Restrict withdrawals in drainages < 25 mi2 and limit withdrawals in drainages 25-50sq
miles to < 1MGD average per day
The following responses to questions posed by EFSAB Facilitators summarize TNC’s contributions relevant to each question:
1. How does this trial balloon/state of the research/research conclusions help the EFSAB to
advise DENR in characterizing the aquatic ecology of different river basins?
We characterized fish community patterns in wadeable streams of four North Carolina river basins, from 141 fish survey sites distributed among the Little Tennessee, Cape Fear, Tar, and Roanoke Rivers. Community patterns were most influenced by precipitation, temperature,
ecological drainage units, and departure from natural land cover associated with the local HUC
12 drainages. These patterns are useful for characterizing the ecology of wadeable streams and
documenting the influence of non-natural land cover on community patterns. These results support the need for environmental flows that protect the naturally variable flow patterns across
as they vary relative to differences in precipitation, river basins, and ecoregions.
We quantified trends in fish diversity and abundance patterns at-a-site over time for the period of
fish survey data 1992-2009. Diversity and abundance changed relative to four different response
patterns: 1.) positive change (>10% increase in diversity or abundance), 2.) negative change (>10% decrease in diversity or abundance), 3.) minimal change (less than 10% change positive
and negative, and 4.) change with no trend pattern (>10% change, no trend pattern). This
analysis may be useful to DWQ or DWR for identifying specific fish survey sites that could be
useful for future monitoring efforts geared toward quantifying the factors that are responsible for
the different response patterns. For example, what is causing increases in diversity at some
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locations and decreases at others? Answering these question would lead to a better understanding of the factors affecting aquatic ecosystem conditions.
2. How does this trial balloon/state of the research/research conclusions help the EFSAB to
advise DENR in identifying the flows necessary to maintain ecological integrity?
We quantified fish flow-ecology response patterns for fish survey sites which occurred downstream of a documented water use source. This only included 10% of the sites (14 locations), the remaining 90% of fish survey sites all occurred upstream of documented water
use sources. A relationship of fish diversity relative to withdrawals, expressed as a percent of
mean annual flow withdrawn for each site, showed a negative trend with a 5-10% decline in fish
diversity relative to withdrawals > 10% of the mean annual flow for a site, and a diversity decline of 25-30% relative to withdrawals > %50 of the mean annual flow for a site. Preventing diversity declines <10% would require limiting withdrawals to < 10% of the mean annual flow
for a site. Our criteria for limiting withdrawals to less than 10% of the monthly median (5% in
drought years) corresponds to a flow discharge less than 10% of the mean annual flow and
protects <10% decline to fish diversity while protecting seasonal flow patterns and flow magnitude differences among river basins and ecoregions.
We analyzed flows for 63 USGS stream flow gages distributed statewide across North Carolina.
For each of these stream gages, we compared flows over two time periods (1955-1980 and 1984-
2012) and examined contemporary trends in flow conditions. We compared flow changes
between the periods using monthly flow percentile metrics for the 90th, 75th, 50th, 25th, and 10th percentiles. Flow changes varied by ecoregion, basin, and flow magnitude. The least amount of change was associated with 90th and 75th percentile flows and the greatest changes occurred with
decreases to the 50th, 25th, and 10th percentile lower flows. Nearly 60% of the gages showed
significant decreases to the 10th percentile flow whereby >50% of the months are experiencing
significant decreases to low flows. For these reasons, we recommend pass-by flows of 60% of the median January – April (50% in drought years) and 50% of the median May – December (40% in drought years) to protect these lower flows from further water use impacts during low
flow and drought periods.
3. Limitations of this trial balloon/state of the research/research conclusions and options
for how to address those limitations?
A limitation with the fish community characterization patterns is that they are constrained to wadeable streams. Using the EDU classification may make up for this limitation as they
inherently include all the stream and river segments within a given EDU and since the patterns
were strong for wadeable stream they should extrapolate to the larger tributaries and mainstems.
The fish-flow-alteration response relationships could be strengthened with more data points. Our work found only 10% of the 141 sites occurred upstream of water use sources, a more
comprehensive statewide analysis would be useful for expanding the number of data points.
As concerns the stream flow analysis, using only contemporary change means we cannot show
larger temporal scale patterns of change over time and we have no unaltered reference condition
from which to assess the role of different influences on changes in flow patterns and whether they are due to natural climatic change, dam operations, or other water resource uses.