of 98
EVALUATION
OF
THE
UTILITY
OF
SEDIMENT
DATA
IN
NASQAN
(National
Stream
Quality
Accounting
Network)
by
Robert
C.
Y.
Koh
Norman
H.
Brooks
Vito
A.
Vanoni
Brent
D.
Taylor
Report
to:
U.S.
Geological
Survey
Contract
No.
14-08-0001-17541
Memorandum
No.
23
June
1983
ENVIRONMENTAL
QUALITY
LABORATORY
California
Institute
of
Technology
Pasadena,
California
91125
i
TABLE
OF
CONTENTS
ABSTRACT
••
CHAPTER
1.
Introduction
••
.
. .
CHAPTER
2.
Basic
Uses
for
River
Sedimentation
Data.
CHAPTER
3.
Characteristics
of
the
Time
Series
for
Selected
Rivers
A.
B.
C.
Introduction
•••••••••
Selection
of
River
Basins
for
Analysis
••
Temporal
Fluctuations
in
Sediment
Transport
••••••••••••
·
.
.
ii
1
3
.12
·
.12
• •
.13
.23
D.
Implications
for
Sampling
Frequency
.37
CHAPTER
4.
Determination
of
Sediment
Yield
by
NASQAN
Data
A.
Introduction.
B.
Conventional
Suspended
Sediment
Rating
Curves
. . . . .
.
.
C.
Modified
Suspended
Sediment
Rating
Curves
.39
.39
.39
.45
CHAPTER
5.
Errors
in
Sampling
Suspended
Sediment
A.
B.
C.
D.
in
Rivers
.60
Introduction.
Effect
of
Unsteadiness.
. . .
.
.60
Effect
of
Sampler
Characteristics
Effect
of
Variable
Transit
Rate
of
the
.60
.64
Sampler.
. . . .
.............
66
E.
Estimating
Unmeasured
Sediment
Discharge
••••
67
F.
Summary..
.69
CHAPTER
6.
Discussion
and
Conclusions
••
••
71
APPENDIX.
Performance
of
Depth-Integrating
Suspended
Sediment
Samplers
••••
.74
A.
B.
C.
Effect
of
Relative
Sampling
Rate.
•••
• •
74
.76
.76
REFERENCES.
D.
E.
Effect
of
Sampler
Alignment
•••
US
Depth-Integrating
Samplers
Fields
Test
of
Samplers
Summary
.88
.91
.94
ii
ABSTRACT
Monthly
suspended
sediment
discharge
measurements,
made
by
the
USGS
as
part
of
the
National
Stream
Quality
Accounting
Network
(NASQAN),
are
analysed
to
assess
the
adequacy
in
terms
of
spatial
coverage,
temporal
sampling
frequency,
accuracy
of
measurements,
as
well
as
~n
determining
the
sediment
yield
in
the
nation's
rivers.
It
is
concluded
that
the
spatial
distribution
of
NASQAN
stations
is
reasonable
but
necessarily
judgemental.
The
temporal
variations
of
sediment
data
contain
much
higher
frequencies
than
monthly.
Sampling
error
is
found
to
be
minor
when
compared
with
other
causes
of
data
scatter
which
can
be
substantial.
The
usefulness
of
the
monthly
measurements
of
sediment
transport
is
enhanced
when
combined
with
the
daily
measurements
of
water
discharge.
Increasing
the
sampling
frequency
moderately
would
not
materially
improve
the
accuracy
of
sediment
yield
determinations.
1
CHAPTER
1
INTRODUCTION
The
purpose
of
this
study
was
to
evaluate
the
usefulness
of
the
sedimentation
data
in
the
National
Stream
Quality
Accounting
Network
(NASQAN).
NASQAN
encompasses
a
wide
variety
of
water
quality
parameters,
including
measurements
of
suspended
sediment
concentra-
tion,
which
is
the
only
component
we
are
considering
in
this
report.
The
overall
objectives
of
NASQAN
are:
(1)
to
define
the
present
conditions
of
water
quality
throughout
the
United
States,
and
(2)
to
identify
changes
or
trends
that
are
taking
place
in
natural
water
quality,
due
to
both
natural
and
human
factors.
The
fully-implemented
NASQAN
program
includes
525
stations
distributed
in
all
hydrologic
regions
in
a
way
which
samples
90
percent
of
the
nation's
surface
water,
except
along
the
seacoasts,
where
many
small
streams
discharge
into
the
ocean.
For
a
more
detailed
description
of
the
NASQAN
network,
its
purposes,
data
analysis
and
evaluation,
see
reports
by
Briggs
and
Ficke
(1979)
and
Controller
General
(1981).
This
study
is
directed
toward
answering
the
following
critical
questions
regarding
the
sediment
data
in
NASQAN:
(1)
With
the
present
NASQAN
system
(sampling
for
the
concentration
of
suspended
sediment
monthly
at
a
network
of
525
fixed
stations),
what
specific
sedimentation
questions
can
be
answered
in
relation
to
primary
NASQAN
objectives
(including
the
computation
of