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FY 1999 ABSTRACTS
ESTIMATION OF FLOW-DURATION CURVES AT UNGAGED STREAM REACHES
IN NEW HAMPSHIRE AND VERMONT
Principal Investigators: Dr.
S. Lawrence Dingman
Descriptors: flow duration, instream flow, water quality management,
water allocation, streamflow depletion, aquatic habitats, New Hampshire,
Vermont
Problem and Research Objectives:
Magnitude and frequency of streamflow are two of the components
of flow regime that together determine the integrity of aquatic ecosystems
through their on impact water quality, energy sources for stream
biota, the physical parameters of aquatic habitat, and biotic interactions.
As all withdrawal uses of water affect the magnitude and frequency
of downstream flows, the problem of instream flows has emerged as
one of the region's major water-resource management issues. It has
been a central issue in most hydropower dam licensing and relicensing
proceedings for the last two decades. New developments such as snow-making
threaten to alter stream regimes in pristine upland watersheds. The
State of New Hampshire has recognized the severity and widespread
nature of these impacts and has been developing an instream-flow
program to develop guidelines and rules for protecting instream flows
threatened by withdrawal uses and flow regulation.
Flow-duration curves (FDCs) are cumulative-frequency plots of mean
daily discharge, hence they depict the magnitude and frequency of
streamflow at a stream reach. They can be readily constructed for
stream reaches which have been gaged continuously for a suitable
period. However, magnitude-frequency information is usually required
for reaches that have not been gaged.
The objective of the research proposed here is to develop improved
techniques for estimating natural FDCs (FDCs unaffected by withdrawal
or regulation) at ungaged stream reaches in New Hampshire and Vermont
. Such curves would provide a baseline against which to evaluate
the effects of proposed water-use, flow-regulation, or land-use developments
on streamflow magnitude and frequency.
Principal Findings and Significance:
Records from 44 gaging stations in NH and VT fit our criteria of
having no significant regulation and at least 10 yr of daily streamflow
records. To facilitate comparison among drainage basins of varying
size, we divided the actual measured flows at these stations by drainage
area to give the specific discharge, q . We then constructed
median-annual FDCs for the specific discharges at each station. Read
more.
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DEVELOPMENT OF STATEWIDE NUTRIENT LOADING COEFFICIENTS THROUGH
GEOGRAPHIC INFORMATION SYSTEM AIDED ANALYSIS
Principal Investigators: Dr. Jeffrey
Schloss, Jody Connor
Descriptors: eutrophication, geographic information systems,
land use, impervious surfaces, land-water interactions, nutrient
loading coefficients, phosphorous, riparian vegetation, spatial
analysis, water quality modeling, watershed management
Problem and Research Objectives:
The waters of New Hampshire represent a valuable water resource
contributing to the state's economic base through recreation, tourism,
and real estate revenues. Some lakes and rivers serve as current
or potential water supplies. For most residents (as indicated by
boating and fishing registrations) our waters help to insure a high
quality of life. New Hampshire currently leads all of the New England
states in the rate of new development and redevelopment. The long-term
consequences of the resulting pressure and demands on the state's
precious water resources remain unknown. Of particular concern is
the response of our waters to increasing non-point source pollutant
loadings due to watershed development and land use activities. While
watershed nutrient budget measurements and modeling have been attempted
on a number of watersheds in the state, the recent cut in the Clean
Lakes Program funding (Section 314) has limited the resources for
current and future watershed diagnostic studies. No previous attempt
has ever been made to review the existing data provided from previous
studies and to investigate whether statewide nutrient loading coefficients
can be developed using the powerful statistical and spatial analysis
tools now available through GIS.
Current water quality models utilized for lake management and diagnostic
purposes (when direct water nutrient budgets have not been measured)
rely heavily on nutrient export coefficients derived primarily from
out of state (Reckow et al ) or limited, in terms of geographic area,
New Hampshire data from Hubbard Brook. This research was initiated
to finally make an effort to review and integrate together the existing
data available from local, state, university, and federal watershed
studies. Developing export coefficients from existing studies conducted
over different areas of the state will allow for the estimation of
watershed loadings with a greater confidence. Such coefficients would
also allow for the efficient use of limited resources and provide
baseline and benchmark data from which future studies can benefit.
Principal Findings and Significance:
- The range of export coefficients for various landcover
combinations (types) found throughout New Hampshire
were summarized for the first time.
- Initial analyses of the data compiled disclosed that
the differences between export coefficients could be better explained
by incorporating other descriptive landscape level data available.
This ranged through a series of spatial scales which ran from:
- Landcover
classification and "typing"
- Generalized subwatershed slope
- Location of potentially impacting land uses
to channelized flow, tributaries or shorelines
- Disturbed land, shoreline development and riparian
buffer and wetland complex extent were other factors that had influence
on the loadings.
- The level of development intensity under forest
cover oftentimes was a major factor that determined where in the
range of loadings a subwatershed fell. GIS data available for analysis
did not allow for accurate estimation of development extent.
- Standardizing the export coefficients to a "normal" precipitation
year decreased the variation within the data set analyzed and brought
coefficients for similar land classes by different investigators
using different techniques slightly closer. However, investigation
into each separate study disclosed the importance of major storm
events in the outcome of the loadings measured for each month when
comparing multiyear studies. Thus, the utility of normalizing the
data may be best for general management purposes or setting target
levels while non-normalized data would be best for diagnostic lake
response modeling for a given year and in management practice evaluations.
- Prediction improvements should occur through the
use of these newly summarized coefficients and ranges over the
existing coefficients used currently and in previous studies which
might have overestimated forested landcover export and underestimated
the range of urban and agricultural land cover export in light
of these results.
The results of this investigation will allow for the improvement
of predictive models used for watershed planning and management.
The benefits of this are wide ranging from assisting watershed stewardship
education efforts throughout the state and region to providing existing
watershed based programs like the EPA Basins Model Initiative, the
statewide Unified Watershed Assessment Initiative (under the federal
Clean Water Action Program) as well as the regional initiative (US
EPA Region 1 and NE states) to develop total daily maximum loading
criteria (TMDLs). The information collected digitized and summarized
will further our modeling efforts of New Hampshire's pristine lakes
and rivers (and similar systems throughout our region). It will also
serve to illustrate the importance (and justification) of proposed
and existing regulations, and best management practices, to decision-makers
and the public.
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