HomeMy WebLinkAbout03_Hydrologic-Stream-Classification-part-3-Jim-MeadPresentation to Ecological Flows Science Advisory Board
January 18, 2011
NC HYDROLOGIC
STREAM CLASSIFICATION
USING SIMULATED
vs.
USGS FLOW DATA
Questions Raised
During the Expert Workshop
Are flow data simulated by the basinwide hydrologic
models comparable to actual USGS recorded flows for
classifying streams?
Different gages have different periods of record. Does the
period of record used in the analysis affect the stream
classification?
To address these questions, additional analyses were
performed by DWR and Environmental Flow Specialists
Neuse Basin USGS Gages
31 Total Unaltered and Altered flow records
14 Class A – Coastal streams
1 Class B –Small Stable stream
3 Class C –Large Stable streams
9 Class D –Small Flashy streams
4 Class G –Seasonal Small streams
zero Class E and F –Large Piedmont rivers &
medium stable streams
Neuse River Basin Gages
Drainage
USGS
Period USGS OASIS class 79 yr OASIS
STATION #GAGE NAME Area of Record class using USGS POR record class
02086500 FLAT RIVER AT DAM NEAR BAHAMA 168.00 1928-1964 A D D
02087570 NEUSE RIVER AT SMITHFIELD 1,206.00 1971-1991 A F F
02091500 CONTENTNEA CREEK AT HOOKERTON 733.00 1930-1975 A F A
0208925200 BEAR CREEK AT MAYS STORE 57.70 1988-2008 B G G
02087500 NEUSE RIVER NEAR CLAYTON 1,150.00 1928-1980 D A A
02088000 MIDDLE CREEK NEAR CLAYTON 83.50 1940-2008 D A A
02091000 NAHUNTA SWAMP NEAR SHINE 80.40 1955-2008 D A A
0208521324 LITTLE R @ SR1461 NR ORANGE FACTORY 78.20 1988-2008 G D D
USGS vs. Simulation Discrepancy
Explanations for Discrepancies
3 of 8 corrected by revisions to classification
models – coefficients for Class D and zero flow
criterion set at zero instead of 0.5
Flat River at Dam near Bahama
Neuse River near Clayton
Little River at SR1461 near Orange factory
All are now Class D for both USGS & simulated
data
Explanations cont’d
Three of these 8 gages ‐Neuse River at Smithfield,
Nahunta Swamp near Shine, and Middle Creek
near Clayton ‐have a portion of their flow record
that appears to be altered.
Determined by EFS using trend analysis.
The simulated flow data, on the other hand, is
completely unimpaired.
Explanations cont’d
Flows for 3 of these 8 stream gages ‐Contentnea
Creek at Hookerton, Nahunta Swamp near Shine,
and Bear Creek at Mays Store –were simulated
based on flows at other locations, NOT from a
node in the basin model at the gage location.
It is therefore not unusual for simulated flows to
be somewhat different than empirical
measurements on a daily timestep – especially for
short‐term events .
79 yr OASIS 20-yr time increments
STATION #GAGE NAME record class1234567
02087500 NEUSE RIVER NEAR CLAYTON A DADAADB
02087570 NEUSE RIVER AT SMITHFIELD F DADAAFB
02089500 NEUSE RIVER AT KINSTON C E C E E C C C
0208758850SWIFT CK NEAR MCCULLARS CROSSROADS G AAAAGGG
02088000 MIDDLE CREEK NEAR CLAYTON A AAAAAGG
02088470 LITTLE RIVER NEAR KENLY A F A A A A A A
02088500 LITTLE RIVER NEAR PRINCETON A F A A A A A A
02091000 NAHUNTA SWAMP NEAR SHINE A F A A A A A A
02091500 CONTENTNEA CREEK AT HOOKERTON A F A A A A F A
Different Class for Different Period of Record
Explanations for
Period of Record Discrepancies
Two of 9 gage discrepancies are eliminated by the
revisions to the coefficients for the Class D model.
(Neuse River near Clayton and at Smithfield)
Four of 9 discrepancies are corrected if the first
year of simulation is removed from the record.
This is an artifact of modeling associated with
establishing the initial conditions in the model.
(Little River near Kenly and near Princeton,
Nahunta Swamp near Shine, and Contentnea
Creek at Hookerton)
Explanations for
Period of Record Discrepancies
The simulated flows for one gage –Neuse River at Kinston –
are at the margin between two classes, particularly for high
flows. Lengthening the interval from 20 to 30 years
resolves the discrepancy.
The last two gages –Swift Creek near McCullars Crossroads
and Middle Creek near Clayton –have many zero
simulation flows towards the end of the record that the
USGS gages actually recorded as very low, but still positive
flows. Extended the analysis interval from 20 to 40 years
resolves the discrepancy.
Conclusions
OASIS has the capability to simulate flow records
for Neuse River Basin locations for up to 79 years.
The longer the POR the more likely the stream
will be classified correctly.
The POR should be entirely unaltered or entirely
altered. There should be no trend inflections or
long term perturbations.
Future hydrologic models should include nodes
at all USGS stations to allow additional
comparisons and checking of simulated versus
measured flow data.
Conclusions cont’d
Simulated daily flows are sometimes less
comparable to measured data in the very low and
low flow range, and the high and very high flow
range. A significant number of simulated zero
flow days can result in a seasonal stream
classification. Abnormally high simulation flows
should be verified, since they can sometimes
result in a class change. A longer analyses interval
(30 or 40 years) usually resolves this issue.
The initial year in the simulation record should
not be included in the classification analysis.