12

of hydrologic processes that occur at a duration greater than 1 day and
less than 1 month. Examination of these errors between different basins
or between different time periods at one site can provide insight into the
dynamics of hydrologic processes that operate for a duration of less than
1 month.

The concept can be expanded to generate synthesized daily flows based
on many different time durations. The error between each of the synthe-
sized daily flows and the measured daily flows represents the relationship
between the different hydrologic processes that blend together to generate
a hydrograph. Long-term trends in these errors indicate changes in the rel-
ative contribution of different hydrologic processes to the site hydrograph
and can provide valuable information for CIA of wetlands by providing a
partial hydrologic explanation for the results obtained using the simple in-
dices and the harmonic analysis.

Root mean square error (RMSE) calculated as

2 WZ
LE - 8)
RMSE = Noss
- where
S = synthesized daily discharge based on successive time
scales .
NOBS = number of observations

RMSE is used to measure errors between recorded and synthesized daily
flows based on different durations. An increase in RMSE beginning in the
decade prior to 1951 is apparent in the decade-by-decade comparisons in
which each decade begins in a year ending in “1.”

The RMSE between pairs of time scales generally increases each de-
cade for the period of record. The shorter time intervals (1 to 3 days, 1 to
7 days) are not as affected over time as the longer intervals. When the de-
cades are offset by 5 years (i.e., the last year of each decade ends in “5”),
the curves change slightly; but the overall increase in decade-by-decade
RMSE for the longer time intervals remains. The same consistent pattern
Temains when the analysis is performed at 5-year instead of decade intervals.
Figure 16 presents an expansion of the time-scale analysis in which error
trends are generated based on daily , 3-, 7-, 15-, 29-, and 59-day average
discharges. In each case, the time series was begun on 1 January of each
year, reset at the end of each year, and restricted to monthly discharges less
than 200 cfs. The analysis was restricted to lower flows based on findings
from the harmonic analysis and discharge-duration curves showing changes
between decades being primarily during low flows. Average daily discharge
values between time increments for each time span were obtained by linear
interpolation (e.g., average daily discharges at Days 2-7 are estimated

Chapter 2 Methods and Results


1961-70

1931-40

4 ‘4

Ce OT

jac ee}

: a ne ae md :

é. be

Fy @

g g

1 1

es a a TTT Ss eT se on
Month Month
1941-50

4

—

a = Bane

oa 2 rer eres

i.

2

&

1

fe ones «6 6 7 8 8 10 1 12
Month Month
1951-60

°

10916 (Flow, cts)

1 2 39 4 § 6 7 6 9 10 1 12

1 2 39 4 5 6 7 8 8 0M 1

Figure 14. Harmonic analysis of the Eleven Point River near Bardley, MO, using two different

scales (Continued)



ELEVEN POINT RIVER NEAR BARDLEY MO

FLOW, CFS

© S$ 10 7S 20 2 3M 35 40 45 30 55 60 8S 70 75 80 85 80 85 100
PERCENTILE

1934-40 yy 1941-50 yg 1951-60
ww as 1961-70 «© 1977-80 «+4 1981-88

Figure 9. Flow distribution for the Eleven Point River near Bardiey, MO

LITTLE RED RIVER NEAR HEBER SPRINGS AR

FLOW, CFS

* :
oO 5 1-43 M2 2S BO SS 40 45 30 5S GD GS 70 75 0 85 BO 8S 100
PERCENTILE

— 1934-40 1944-50 + 1951-60
-=2+-1961-70 gg 1977-80 1981-85

Figure 10. Flow distribution for the Little Red River near Heber Springs, AR


Cache River at Patterson, AR Eleven Point River Near Bardley, MO
w00 1000
& 1200 8 ‘
gm SS y pas
i - eee 3 Ny Se
: een Eo SSE,
“00
ae
200 20
Sees taste ewan aie arian tastao asia) wonrgo_wosao evo
—— RMSEN 1S days -—— RMSER ET days ——— AMSES 1-15 deys RMSE 1S.days mmm RISER 1-7 days oma RMSES 1-15 days,
—————" AIMSE4 1-29 days “""""" RMSES 160 days momen PMSES 1-29 days onnnn> RMSES 1-59 days
Buffalo River Near St. Joe, AR Little Red River Near Heber Springs, AR
- 00 = —
 sx00 t. [Scam
y 0 q ee \
§ scxo
1.00
100
0
avian verso evan wets tan eta ena Sowise warty este tata vote foot
——— PMSEL 1S days —m— PMSEZT-Tdeys ——— AMSES1-15 cays PMSET 13 days: RMSE 1-7 days PMSES 1-15 cays.
PSEA 1.20 days nome POSES 1.00 dave crnmne PMSEA 129 dayn eeens RMSES 1.60 6070

Figure 17. Comparison of respective root-mean-square errors (RMSE) of streams examined with
time-scale analysis. All recorded flows are considered for each stream


or characterizing the effects of wetland alteration on hydrologic patterns.
The 75- or 90-percent exceedance discharge range conveniently describes
low discharges in a system while not overemphasizing single extreme low
values. The 10- or 25-percent exceedance discharge can be used to describe
high discharges without being overly influenced by a single extremely
high measurement. The effect of a particular wetland modification on wet-
land hydrology can often be initially described using discharge-duration
curves. However, changes in hydrologic patterns using discharge-duration
curves are difficult to discern because so many curves are required

(60 curves - 12 months times 5 decades) to describe long-term trends.
Flow-frequency trends of the Cache River at Patterson for the decades of
interest are summarized in Figure 6, while distribution of flows of the
Cache River at Patterson is compared with three other streams in close
geographic proximity and with median flows of about the same magnitude
in Figure 7. Flow distributions of the Buffalo River, the Eleven Point
River, and the Little Red River are found at Figures 8, 9, and 10.

Complex indices and summary methods

The indices that follow are formulated to describe temporal patterns in
a series of hydrologic data such as are commonly available from long-term
gauge records. They may be more difficult to employ than the simple indi-
ces, but they can depict subtle changes in hydrologic trends with potential
biological significance. Because many wetland biota require different hy-
drologic conditions at each of their life stages, understanding long-term
hydrologic patterns as well as focusing on specific months is critical. Con-
sequently, it is important to view the effects of a wetland alteration in /
terms of its overall effect on annual hydrologic patterns. Assessing the ef-
fect of a wetland alteration using annual or monthly summaries restricted
to 1 or a few years or months may result in misleading conclusions. |

Advanced hydrologic methods (e.g., spectrum analysis using Fast Fou-
rier Transformation) are also available, but are not generally employed in
cumulative impact analysis because of resource or training limitations and
difficulty of interpretation. The following methods have been adapted or
developed because they are mathematically simple and easy to apply, and
the results are relatively easy to interpret. More importantly, they have a
resolution and scale selected to facilitate relating biological processes to
hydrologic patterns. While the focus of this paper is riverine wetlands,
harmonic analysis and time-scale analysis can also be used to describe or
assess changes in water surface elevation patterns in lacustrine (lake)
wetlands.

The results obtained for the Cache River are compared with other sites
in the region because of changes in the procedures used to collect stage
data that could affect the results of the analysis. The effect of changes in
data recording or confounding effects of global climate change would be
inferred if similar trends are observed across multiple basins.

Chapter 2 Methods and Results


16

of groundwater levels indicate a gradual and consistent reduction in
groundwater levels (Tighe, in preparation). This same relationship be-
tween alteration of drainage characteristics in a basin and wetland hydrology
has been observed at other sites (Roulet 1990). However, it may be im-
possible to determine the effects of altered hydrologic patterns on the
fauna and flora of the unimpacted Cache River wetlands because ongoing
studies can only document present wetland conditions.

The CIA studies conducted on the Cache River have demonstrated that
changes in the basin and wetlands have probably contributed to specific
changes in hydrologic patterns in the wetlands. The computational tools
identified in this report may be useful for characterizing hydrologic pro-
cesses producing impacts likely to affect wetland vegetation, wildlife, and
aquatic biota in the Cache River System. However, these changes may be
unique to the Cache River and should not be extrapolated to other wet-
lands. Each wetland should be analyzed individually.

This technical report presents a suite of hydrologic indices and sum-
mary variables with potential for describing and exploring the effects of
hydrologic perturbations that can contribute to impacts on wetlands.
These indices range from intuitively simple but generally insensitive indi-
ces such as means, medians, ranges, and discharge-duration curves to indi-
ces that are sensitive to subtle changes in hydrologic patterns. One such
sensitive index, provided in harmonic analysis, is relatively simple to per-
form and useful to explore changes in the pattern of discharges or stages
in wetlands. The time-scale analysis can be employed to provide a rela-
tively high resolution quantification of changes in hydrology that can be
related to long-term changes in land or water use patterns linked to the
changes in wetlands. ,

The hydrologic analyses presented here can be used as the basis of
CIA. From a cumulative impact assessment standpoint, any alteration of
the wetland that causes the low flow hydrograph of the Cache River to be
more “flashy” by eliminating base flow or increasing runoff rates will con-
tribute to the further degradation of the historical hydrologic pattern of
the wetland and should either be avoided, mitigated, or minimized. Con-
versely, any activity that shifts these patterns towards 1930-1940 patterns
should be encouraged. If cause-and-effect linkages between land use pat-
terns, hydrologic time scales, and biotic response can be determined, then
determination of cumulative impacts resulting from hydrologic changes on
wetlands is possible.

Chapter 3 Conclusions and Summary


1931-40

Sa EE SE,
a

1941-50

‘
°
bad o o
°

§) oo.
flea 2 te
é °
£ <a

40910 (Flow, et)

1961-70

1 2 8 « 8 6 7 8 8 © 1 1

rt
1971-80
ca
ae “os °
e
° - ae ea
. °
eT
Fa on

Figure 14. (Concluded)



Corps of Engineers Research Report Summary, Sep. 1994

Wetlands:
Impact Assessment

WY

Cumulative Impact Analysis of Wetlands:

(TR WRP-SM-3)

ISSUE:

In order to make informed decisions concerning
cumulative impact analysis of wetlands, the
Corps of Engineers Districts and other wetlands
professionals need data often not directly avail-
able. Cumulative impact assessment of wet-
lands includes relating historic patterns of flow,
derived from the stream’s flow record, to
changes in the watershed associated with that
stream. Harmonic analysis and time-scale anal-
ysis were applied to selected stream records to
ascertain their potential for describing cumula-
tive impacts.

RESEARCH:

The study area chosen included selected streams
in the White River basin, Arkansas/Missouri.
The Cache River received particular emphasis
because a significant amount of information was
readily available concerning it and its surround-
ings. Daily flow values were retrieved from
each of the streams. Using nonlinear, harmonic
analysis as well as time-scale analysis (a tech-
nique adapted from fractal geometry) to reveal
the time-dependent patterns in the respective

Hydrologic Indices

samples, the results were compared decade-by-
decade to discern changes in the historic, seasonal
patterns. Other streams in the White River basin
were analyzed in the same manner and compared
with the Cache River, noting historic changes in
land use and stream regulation.

SUMMARY:

The study identifies methods with the potential to
differentiate historic time frames in which disrup-
tions were likely to have occurred. The methods
appear to be translatable to other geographic areas
where streamflow is typically seasonal.

AVAILABILITY OF REPORT:

The report is available on Interlibrary Loan Ser-
vice from the U.S. Army Engineer Waterways
Experiment Station (WES) Library, 3909 Halls
Ferry Road, Vicksburg, MS 39180-6199, or
telephone (601) 634-2355.

To purchase a copy, call National Technical
Information Service (NTIS) at (703) 487-4650.
For help in identifying a title for sale, call (703)
487-4780. NTIS report numbers may also be
requested from the WES librarians.



Cache River at Patterson, Arkansas

‘00000

Log CRange, cfs)

00

1 2 3 or er er er Tr, cs
Month

— 1827-40 9 1847-50 ig 1951-50
1957-709 1977-80 4. 1981-88

Figure 5. Decade-by-decade comparison of monthly ranges.of flows

CACHE RIVER AT PATTERSON AR
‘sp0000

FLOW, CFS

0 5 1 15 20 25 30 35 40 45 50 55 60 85 70 75 80 8S 80 85 100
PERCENTILE

—— 1921-40 ge 1947-50 yg 1954-60
wo=+1961-70 gg 1877-80 +. 1981-88

Figure 6. Decade-by-decade comparison of flow distribution


from Week 1 discharge of 100 cfs and a Week 2 discharge of 170 cfs as
110, 120, 130, 140, 150, and 160 cfs). Comparisons are made between dis-
charges at 5 intervals: (a) daily to 3 days, (b) 1 to 7 days, (c) 1 to 15

days, (d) 1 to 29 days, and (e) 1 to 59 days to characterize changes in hy-
drologic patterns in the Cache River at low discharges.

The time-scale analysis on the Cache River at Patterson was repeated
using discharges exceeding 40 cfs because the methods used to collect
stage-discharge information prior to October 1949 may have used default
values of 40 cfs for low flows. Regression analysis of the respective root
mean squares of data including and not including flows 40 cfs or less re-
vealed that the two sets of data were significantly correlated (p < 0.01)
and that the inclusion or rejection of the suspect data did not change the
conclusions obtained from the analysis (Figure 16), i.e., that flow was
more uniform before 1950 than afterward.

Other gauges in the area were examined in like fashion to determine if
they were similar to the Cache River. These were Buffalo River near St.
Joe, AR, Eleven-Point River near Bardley, MO, and Little Red River near
Heber Springs, AR. Characteristics of various streams at/near the speci-
fied gauge locations are given at Table 2. The flow limits of the Buffalo
River and Eleven Point River were set to the same upper and lower
bounds—200 and 40 cfs, respectively—as were applied to the Cache
River at Patterson. When these results failed to show “definition,” the
analyses were rerun using all flows in the RMSE calculations. The RMSE
values of each of the streams compared with the Cache River at Patterson
(all flows considered) are graphed in Figure 17.

Table 2
Characteristics of Streams/Gauges Considered
Daily Flow, cts
Drainage
Gauge Area, sq mi| River Mile | Maximum | Mean Minimum
Cache River
at Egypt 701 143 8,940 827 0
at Patterson 1,037 772 12,100 1,257 o
at Cotton Plant 1,172 10,900 1,351 25
Buffalo River near St. Joe 829 58.3 158,000 1,026 6.6
Eleven Point near Bardley 793 53.7 26,800 771 152
(1921-1992)
Little Red River near 1,648 31.7 35,300 2,459 to)
Searcy
Little Red River near 1,153 78.8 117,000 1,764 to)
Heber Springs (1927-1980)

In the analysis of the Buffalo River, all of the respective intervals
(RMSEI-5) seem uncharacteristically low in the decade of 1931-40 when

‘Chapter 2 Methods and Results


Technical Report EL-93-3, U.S. Army Engineer Waterways Experi-
ment Station, Vicksburg, MS.

Peitgen, H.-O., and Richter, P. H. (1986). The beauty of fractals.
Springer-Verlag, New York.

Roulet, N. T. (1990). “Hydrology of a headwater basin wetlands:
Groundwater discharge and wetland maintenance,” Hydrological Pro-
cesses 4, 387-400.

SAS Institute, Inc. (1988). “PROC NLIN” (computer program), IBM-PC,
SAS Institute, Inc., Cary, NC.

Schlosser, K. J. (1991). “Stream fish ecology: A landscape perspective,”
BioScience 41(10), 704-712.

Shedloc, R. J., Wilcox, D. A., Thompson, T. A., and Cohen, D. A.
(1993). “Interactions between ground water and wetlands, southern
shore of Lake Michigan, USA,” Journal of Hydrology 141, 127-155.

Spaling, H., and Smit, B. (1993). “Cumulative environmental change:
Conceptual frameworks, evaluation approaches, and institutional per-
spectives,” Environmental Management 17(5), 587-600.

Stakhiv, E. Z. (1988). “An evaluation paradigm for cumulative impact
analysis,” IWR 88-PS-3, U.S. Army Engineer Institute for Water Re-
sources, Fort Belvoir, VA.

Sumner, R. (1991). “Wetlands research update,” U.S. Environmental Pro-
tection Agency, Environmental Research Laboratory, Corvallis, OR.

Suso, J., and Llamas, M. R. (1993). “Influence of groundwater develop-
ment on the Dofiana National Park Ecosystems (Spain),” Journal of
Hydrology 141, 239-269.

Tighe, B. “Groundwater conditions in the Cache River basin,” Technical
Report in preparation, U.S. Army Engineer Waterways Experiment Sta-
tion, Vicksburg, MS.

Trémoliéres, M., Eglin, I., Roeck, U., and Carbiner, R. (1993). “The ex-
change process between river and groundwater on the Central Alsace
floodplain (Eastern France),” Hydrobiologia 254, 133-148.

Trost, N. (1991). “Approximation of data-rich time series by harmonic
analysis,” Ecological Modelling 56, 259-266.

Turcotte, D. L. (1992). Fractals and chaos in geology and geophysics.
Press Syndicate of the University of Cambridge, New York.

19


3 Conclusions and Summary

The hydrological analyses presented herein, particularly the harmonic
analysis and time-scale analysis, all indicate that patterns in low flows
(less than 200 cfs) at the Patterson gauge of the Cache River have changed
gradually and consistently from the decade of the 1950s to the present. This
analysis suggests that low discharges during the decades prior to 1950
were dominated by hydrologic processes (possibly groundwater recharge,
water stored within the watershed by forested land, or water stored within
the wetland; but since appropriate records are unavailable, this can only
be inferred on the basis of literature findings from other wetlands) that
provided a generally stable base discharge. Consequently, during periods
of prolonged drought, the low discharge hydrograph was dominated by a
generally persistent and stable hydrologic process prior to 1950. After
1950, the error between daily flows based on different time scales in-
creased. The timing and duration of low discharges from the decade of
the 1950s to the present are probably increasingly dominated by some hy-
drologic process operating over a short time period and not by ground-
water recharge or recharge from stored water within the basin or wetland.
Armstrong and Garwood (1991) describe the effects of drainage on runoff
characteristics. Similar links between groundwater and wetland hydrol-
ogy have been observed at other sites (Lloyd et al. 1993; Armstrong and
Garwood 1991; Gehrels and Mulamoottil 1990; Suso and Llamas 1993;
Shedlock et al. 1993; Bernaldez, Rey Benayas, and Martinez 1993), and
the interplay between groundwater and streamflow is well known
(Trémoliéres et al. 1993; Bickerton et al. 1993). Clear-cutting of forest or
conversion to grassland also alters flow frequencies (Burt and Swank
1992; Anderson et al. 1993; Gustard and Wesselink 1993; Calder 1993).

The effect of changes in the low flow hydrograph on spatial patterns
and wetlands fauna are presently the topic of ongoing work and will be
documented in another report. Preliminary analyses suggest that ground-
water pumping, as indicated by acreage planted of crops requiring irriga-
tion, has increased at a rate that corresponds to the loss of pattern indicated
by the harmonic and time-scale analysis. Relatively short duration records

1 Preliminary analysis of other data indicates there is sufficient head to cause the wetland to be a
groundwater discharge area during much of the year (Kleiss 1993).

Chapter3 Conclusions and Summary 15


Distribution of Flows from Respective Perlods of Record
‘10000
1000
o
¢
o
el
a
ob
‘4 a
3 40 45 20 2 3 35.40 45 SO SS 60 85 70 75 GO BS AO MS
Percentite
ae Eleven Point River near Gardley MO @- Littie Red River peer Heber Sorings AR
a Buffalo River near St. Joe AR —— Cache Biver at Patterson AR

Figure 7. Distribution of flows of comparable streams in the White River basin,
Arkansas/Misssouri

BUFFALO RIVER NEAR ST. JOE AR

‘1000000

FLOW, CFS

© 5 1 15 20 25 90 35 40 45 30 35 @0 G5 7 75 @O BS MO 95 100
PERCENT ILE

1931-40 ye 1944-50 yg 1951-60
1961-70 ¢ 1977-80 + 1981-90

Figure 8. Flow distribution for the Butfalo River near St. Joe, AR


10

not begin until September 1927. Moreover, the station was discontinued
as a continuous-record station and converted to a crest-stage partial-record
station in September 1980. Most importantly, the flow has been com-
pletely regulated since March 1962 by Greers Ferry Dam, with some regu-
lation from October 1960 to February 1962 by the construction of Greers
Ferry Dam. River regulation has had a profound effect on harmonic pat-
terns of flow in the Little Red River. In the decade prior to regulation, the
minimum monthly mean reached an extreme low (<10 cfs) near the end of
the year, but the decade of the regulation showed a very constant minimum
for all months of the year (~100 cfs). In the decade of 1971-80, the mini-
mum exceeded 100 cfs for all months, varying in a markedly different
way from the mean and the maximum.

To explore further which part of the flow range was affected, correla-
tion analysis among minimum, maximum, and mean monthly discharges
was performed for each stream. High correlations between mean, mini-
mum, and maximum discharges for a single site imply that extremes in
wet and dry periods tend to fall within the same general hydrologic pat-
tern as the mean monthly discharge summary, whereas low correlations
suggest that extended (monthly) extreme discharge conditions occur ran-
domly or in a pattern different from mean monthly discharges. Conse-
quently, trends in correlation coefficients among decades can be used to
deduce in which part of the hydrograph changes in flow patterns have oc-
curred. Correlation statistics by decade and among mean, minimum, and
maximum monthly (weekly) means for the gauges on the Buffalo River
near St. Joe, AR, the Eleven Point River near Bardley, MO, the Little Red
River near Heber Springs, AR, as well as on the Cache River at Patterson,
AR, are given in Table 1.

It is reasonable to expect the changes in hydrology identified by har-
monic analysis to affect aquatic and/or wetland biota requiring certain sea-
sonal hydrologic patterns for successful completion of their propagation
and/or early life stages (Bayley 1991). Harmonic analysis was useful in
detecting changes in hydrologic patterns in the Cache River, particularly
in the behavior of minimum mean flows. However, its usefulness was
limited by not providing enough insight into the factors responsible for
the decade-to-decade changes. From the standpoint of cumulative impact
analysis, the harmonic analysis did not generate sufficient information to
correlate with land-use changes or other long-term changes in the basin
that could, in turn, be used to understand why the hydrologic patterns may
have changed. To supplement the harmonic analysis, comparative time-
scale analysis was performed on the Cache River discharge data.

Comparative time-scale analysis. Many time series exhibit pro-
nounced time-scale dependent behavior. For example, tide gauge informa-
tion can be decomposed into a number of different harmonic patterns,
each based on a different period and each representing the effects of sepa-
rate influences on tide dynamics (i.e., diel, lunar, solar, localized, and in-
teractive influences). Similarly, stream gauge readings can also exhibit
pronounced time-scale dependent behavior because many of the separate

Chapter 2 Methods and Results


describe long-term changes in wetland hydrology relative to a single action
will allow the effects of that action to be assessed against historical trends
and patterns, thereby facilitating an understanding of the single impact
within the context of past impacts on wetland hydrology.

Purpose

The CE, like the other agencies involved in wetlands preservation, is
unable to consider cumulative impacts in its environmental assessments of
wetlands impacts because of the unavailability of appropriate evaluation
tools. Finding a simple means to describe, quantify, and isolate the historic
H&H influences on a wetland would enable planners to deduce the hydraulic
and hydrologic (H&H) processes responsible for current and perhaps future
wetland conditions. Applications of relatively simple indices and summaries
derived from flow and/or stage records, referred to as “hydrologic indices,”
to the Cache River wetlands are presented in this technical report as a
case study of CIA. The concepts and methods presented in this report are
most applicable to riparian wetlands. However, they can be easily modi-
fied for application to other wetland types. Where possible, suggestions
are provided regarding how these modifications could be made.

A comparison document dealing with the climatic and agricultural
impacts is in preparation.

Chapter 1 Introduction


(p30 yeeys) “py eunBi4

‘Be-186t G16). OL-196) Oo ts6h Osby) orizst, 8s-186 Likeaad 02-1961 O-1S6) ‘OSby6$ Or-tz6L
7 r +

T T T T THF

[eepen-—wowpey.... unum =--— —_Usey ===]
det den

a
42
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3 s
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. 4zse
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: ees oes _oxises __opusa__opspsi_ ores
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ast qs

(619 "moa) 0180}
(}0 ‘mots) 0160



BUFFALO RIVER NEAR ST. JOE, ARKANSAS

~ AN ia
seoee |
veo
g
3
“exo 7e20 7e00 Taso Feo 7370 Te00 7380
‘veor
ae MEAN me MEDIAN |g MINIMUM a MAXIMUM
ELEVEN POINT RIVER NEAR BARDLEY, MISSOURI
seo0ee
soooo
:
2
‘20 Je30 730 7350 Ta00 7370 7960 Ta00
‘reer
a MEAN We MEDIAN a MINIMUM ge MAXIMUM
LITTLE RED RIVER NEAR HEBER SPRINGS, ARKANSAS
soscen
sooo b
coe -\
‘
&
aed
. LNA
| i\ {
‘azo 1930 1940 1950 1960 1970 7990
veer
we MEAN we MEDIAN La MINIMUM og MAXIMUM

Figure 3. Simple annual statistics of stream flows of the Buffalo River, the
Eleven Point River, and the Little Red River


vi

Preface

The work described in this report was authorized by Headquarters, U.S.
Army Corps of Engineers (HQUSACE), as part of the Stewardship and
Management Task Area of the Wetlands Research Program (WRP). The
work was performed under Work Unit 32757, Cumulative Impact Analysis,
for which Dr. John M. Nestler, Environmental Laboratory (EL), U.S. Army
Engineer Waterways Experiment Station WES, was the Principal Investiga-
tor. Mr. Sam Collinson (CECW-OR) was the WRP Technical Monitor for
this work. :

Mr. David Mathis (CERD-C) was the WRP Coordinator at the Directorate
of Research and Development, HQUSACE; Dr. William L. Klesch (CECW-
PO) served as the WRP Technical Monitors’ Representative; Dr. Russell F.
Theriot, WES, was the Wetlands Program Manager. Mr. Chester O. Martin,
WES, was the Task Area Manager.

Participants in the study, in addition to the authors, included Mr. Daniel
Thompson, who provided assistance in the collection and processing of
the historical data, and Drs. L. Jean O’Neil, Dara Wilber, and Mr. Bob Tighe
who provided insight through discussion of their work pertaining to this
effort and who offered critical review and suggestions regarding inclusion
of other locations to analyze in draft versions of this report. This report
was written by Dr. Nestler, Water Quality Modeling Branch (WQMB),
Ecosystem Processes and Effects Division (EPED), EL, and Ms. Katherine
S. Long, EPEB, under the direct supervision of Dr. Mark Dortch, Chief,
WQMB, Dr. Richard E. Price, Acting Chief, EPEB, and Mr. Donald
Robey, Chief, EPED, and under the general supervision of Dr. John
Keeley, Assistant Director, EL, and Dr. John Harrison, Director, EL.

At the time of publication of this report, Director of WES was
Dr. Robert W. Whalin. Commander was COL Bruce Howard, EN.


Contents

Preface... ee ee ee tee vi
J—Introduction .. 1... 6 ee ee ees 1
Background ... 2... 2. eee eet ee eee eet 1
Purpose 2... eee ee tee 2
2—Methods and Results... 6... eee ee ee ee 3
Hydrologic Indices... 1. ee et eee 3
Cache River Site Description... . 1... 66+ steerer eee 4
Simple indices and summary variables .......---+-+++- 5
Complex indices and summary methods ......-------> 6
3—Conclusions and Summary ......- 2-2 - eee eee eee 15
References... 0. ee eee ee eee 17

Figures 1-17
SF 298


hydrologic factors that blend together to generate a characteristic pattern
at a gauge each have an associated unique time scale. For example, snow-
melt can increase summer flows for a period of a month to several months
(Changnon, McKee, and Doesken 1991). Groundwater recharge can pro-
vide a relatively constant base flow. Seasonal rainfall patterns associated
with the passage of fronts will result in periods of increased flows lasting
several months during a seasonal wet period. Conversely, synoptic rainfall
events associated with localized summer rain storms occur more or less ran-
domly and will influence gauge records for a period of up to 1 week, depend-
ing upon the duration and intensity of precipitation, runoff characteristics
of the basin, and the area of the basin covered by the storm. Changes in
the importance of different hydrologic factors in a long period of record
can be assessed by evaluating changes in time-scale behavior at intervals
along the record. A variety of methods, most based on application of
arithmetic moving average methods (e.g., ARMA—auto-regression moving
average), are available to assess time-scale behavior. However, these
methods have limited usefulness for CIA because they require advanced
training, the results are often difficult to interpret, and their primary utility

is to synthesize data instead of providing direct insight into changes in
hydrologic processes. .

Studies in fractal geometry (Peitgen and Richter 1986; Turcotte 1992)
suggest that seemingly complex physical features, such as stream net-
works, mountain ranges, and clouds, and complex physical processes,
such as turbulence and stream flow patterns, exhibit the same pattern re-
peatedly; but over increasingly smaller distances or time scales, they ex-
hibit “fractal properties.” For example, the margins of a cloud, when
viewed from a distance, exhibit gentle billows. However, as the observer
moves closer to the cloud, the large billows are seen to be comprised of
smaller billows comprised of still smaller billows until a limiting scale is
approached.

An important fractal property, the fractal dimension, is commonly ob-
tained using a “method of rulers.” In this approach, progressively larger
tulers are used to measure the perimeter of physical feature. A straight-
line relationship between the common logarithm of both ruler length and
perimeter is indicative of strong fractal properties (the slope of this line
is termed the “fractal dimension”). This relationship implies that a single
underlying pattern is being repeated, but at different scales, within the
feature.

Hydrologic time series are also known to exhibit fractal properties. For
the Cache River application, these properties were described using discharge
averages (“time dimension”) based on different durations instead of rulers of
different lengths (“distance dimension”). However, the concept of evaluating
information lost as a function of the resolution of measure is similar. Mean
monthly flows were calculated for each month for the period of record. Syn-
thesized daily flows were obtained by linear interpolation between adjacent
months. The error between the synthesized daily flows based on monthly
means and the measured daily flows represents primarily the contribution

Chapter 2 Methods and Results

11


1 Introduction

LS

Background

The accumulated effect of many individual development activities,
none of which is large or damaging by itself, may collectively produce
major changes in wetlands functions, thereby degrading environmental
quality. The importance of cumulative impacts on wetlands integrity is
well-documented and is great enough that the National Environmental
Policy Act requires that the Corps of Engineers (CE) and other agencies
having a regulatory or stewardship responsibility for wetlands consider
cumulative impacts in their environmental assessments of wetlands. Syn-
ergistic effects of several different individual impacts may collectively
produce a different impact from the sum of the individual impacts (Stakhiv
1988; Granholm et al. 1988; Gosselink et al. 1990; Sumner 1991; Leibowitz
et al. 1992; Davies 1991; Spaling and Smit 1993).

Cumulative-impact assessments and single-impact assessments of wet-
lands differ. Single impact assessments usually focus on a specific activity
that affect wetlands, such as draining, filling, or channelization, with the
specific nature of the impact helping to direct and to focus the activities
of regulatory and stewardship agencies. In contrast, cumulative impact as-
sessment of wetland integrity is more difficult because the many impacts
that have accumulated to characterize the present state of a wetland may
be widely dispersed over many decades, occur throughout a river basin,
and often are difficult to define or characterize because necessary data on
present and historical land use or water use practices are lacking (Cocklin,
Parker, and Hay 1992). In addition, cumulative impact assessment (CIA)
must not summarize and synthesize only individual impacts over time and
space, but must also address interactions of individual impacts (Spaling
and Smit 1993).

The CIA approach described in this technical report uses hydrologic in-
dices to describe changes in long-term discharge patterns of rivers. These
hydrologic indices may be linked with other information (e.g., spatial pat-
terns in wetlands) to form cause-and-effect sequences between wetland hy-
drology, wetland spatial patterns, and wetlands functions, affecting habitat
value (Croonquist and Brooks 1991). Developing and applying indices to

Chapter 1 Introduction


References

Anderson, H. A., Miller, J. D., Gauld, J. H., Hepburn, A., and Stewart, M.
(1993). “Some effects of 50 years of afforestation on soils in the
Kirkton Glen, Balquhidder,” Journal of Hydrology 145, 439-451.

Armstrong, A. C., and Garwood, E. A. (1991). “Hydrological conse-
quences of artificial drainage of grassland,” Hydrological Processes 5,
157-174.

Bayley, P. B. (1991). “The flood pulse advantage and the restoration of
river-floodplain systems,” Regulated Rivers: Research & Management
6, 75-86.

Bern4ldez, F. G., Rey Benayas, J. M., and Martinez, A. (1993). “Ecologi-
cal impact of groundwater extraction on wetlands (Duoro Basin,
Spain),” Journal of Hydrology 141, 219-238.

Bickerton, M,, Petts, G., Armitage, P., and Castella, E. (1993). “Assess-
ing the ecological effects of groundwater abstraction on chalk streams:
Three examples from eastern England,” Regulated Rivers: Research &
Management 8, 121-134.

Burt, T. P., and Swank, W. T. (1992). “Flow frequency responses to
hardwood-to-grass conversion and subsequent succession,” Hydrological
Processes 6, 179-188.

Calder, I. R. (1993). “The Balquhidder Catchment water balance and pro-
cess experiment results in context—What do they reveal?,” Journal of
Hydrology 145, 467-477.

Changnon, D., McKee, T. B., and Doesken, N. J. (1991). “Hydroclimatic
variability in the Rocky Mountains,” Water Resources Bulletin 27(5),
733-743.

Cocklin, C., Parker, S., and Hay, J. (1992). “Notes on cumulative envi-
ronmental Change I: Concepts and issues,” Journal of Environmental
Management 35, 31-49.

References

17


US Army Corps

of Engineers
Waterways Experiment
Station

nl

Wetlands Research Program Technical Report WRP-SM-3

Cumulative Impact Analysis of Wetlands
Using Hydrologic Indices

by John M. Nestler, Katherine S. Long

September 1994 — Final Report F
Approved For Public Release; Distribution Is Unlimited


13. (Concluded).

The study identifies methods with the potential to differentiate historic time frames in which disruptions
were likely to have occurred. The methods appear to be translatable to other geographic areas where
streamflow is typically seasonal.

14, (Concluded)

Cache River Cumulative impact assessment
Daily values Environmental impact
Harmonic analysis Hydrology

Nonlinear regression Root-mean-square error
Streamflow Time-scale analysis

White River


Cache River Site Description

The Cache River basin, located in northeastern Arkansas 162 km up-
stream from the mouth of the White River (Figure 1), has been designated
as a Ramsar! site. The gauging station of particular interest in the Cache
River basin is located at Patterson, AR, and measures the primary inflow
to the Cache River study area. The Patterson gauge has recorded the flow
of the Cache River from a drainage basin of approximately 2,685 sq km
for more than 60 years from January 1928 to the present. Because of the
extensive coverage throughout time and the ready availability of comple- .
mentary data, the Patterson gauge data were chosen to illustrate the hydro-
logic indices presented in this paper. Other gauges on the Cache River are
at Egypt (draining an area of 1,815 sq km) and Cotton Plant (draining an
area of 3,036 sq km), the location where primary outflow is measured.
The Patterson and Cotton Plant gauges are approximately 49 river km
apart. The location of the wetland of ptimary interest occupies about
350 sq km of the lower part of the drainage basin, with about 60 sq km
of this area in bottomland hardwood forest. The wetlands upstream have
undergone extensive channelization in the 1920s and 1930s to permit
agricultural development in the area.

Questions concerning consistency of data collection methods or con-
founding effects from global climate change or decades-long drought cycles
commonly arise during evaluation of long-term gauge data. Methods of
data collection commonly change as technologies mature or change. In
the case of the Cache River, the Patterson gauge was manually read at
0700 hours each morning until October 1949. Consequently, the pre-1949
gauge records are instantaneous measurements based on one daily observa-
tion. All subsequent readings are based on average daily stages from auto-
matic stage recorders. Additionally, gauge readings collected prior to
1950 were characterized by flow values consistently above 40 cfs.
Whether or not these readings represent inadequate calibration of the gaug-
ing sites or reflect actual flows in the river is uncertain. To address these
data uncertainties, the results of some of the more innovative indices were
compared with and without the suspect data included.

The effects of global climate change or long-term drought cycles are ad-
dressed by including in the analysis several other complementary gauging
sites within the same basin or in nearby basins. Long-term results from
these supplementary gauges were compared with results from the Cache
River site to determine if hydrologic patterns in the Cache River were af-
fected by alteration of internal hydrologic processes or external changes
in climate, such as global warming or drought.

1 This site has been designated by the U.S. Fish and Wildlife Service to receive special study as
‘one of a group of internationally recognized wetlands of critical ecological significance.

Chapter 2 Methods and Results


2 Methods and Results

Hydrologic Indices

The hydrologic pattern for a specific riverine wetland is based on a
complex interplay of numerous factors that determine timing and magnitude
of discharges in rivers. Understanding hydrologic patterns is important be-
cause nearly all significant wetland processes can.be wholly or partially
described in hydrologic terms. Similarly, many alterations to wetlands
(e.g., filling, draining, and stream regulation) can be characterized in
terms of their alterations on the prevailing hydrologic regime (Schlosser
1991; Ehrenfeld and Schneider 1991). Thus, long-term changes in hydro-
logic patterns of wetlands may be used as a template upon which cumula-
tive impacts can be identified, interpreted, and assessed. In addition,
changes in spatial patterns of wetlands vegetation, described using tools
such as the geographic information system (GIS), may be interpreted rela-
tive to changes in wetlands hydrology. Changes in hydrology and spatial
patterns may be further linked to associated changes in other wetland values
and functions to complete a CIA.

A variety of indices and summaries are available to describe hydrologic
patterns in streams. They can be used to describe hydrologic patterns or to
describe the hydrologic effects of wetland alteration on stream discharge pat-
terns. The hydrologic indices presented here are based on long-term
stream gauge data. Stream gauges record water elevations at specific loca-
tions, usually at specific intervals in river basins. These records of water
elevation can usually be converted to estimates of mean daily flow. Stream
gauges are deployed by a number of agencies, including the CE. The
United States Geological Survey (USGS) maintains the most extensive net-
work of stream gauges in terms of areas and times covered. Combined
with runoff and drainage area information, synthesized gauge information
for ungauged sites may be deduced from patterns in gauged streams
within the basin.

Chapter 2 Methods and Results


40 cfs < Flows < 200 cfs

(E-=RMSET —--RMSE2_°+ RMSE3_—-RMSE4 ——RMSES]

1921-40 1941-60 1951-60 1961-70 1971-80 1981-90
‘Time Period

Cache River at Patterson, All Flows Less Than 200 cfs

800
[---RMSE1_--- RMSE2_——RMSE3_—--RMSE4 —-RMSES] _/
700+ /
00 |
g
§ sot
‘400 |
E 300
i 200
100 +
0
1921 1941 1951 1961 1971 1981
‘Time Period beginning in Year _

Figure 16. Root-mean-square error (RMSE) of flows of the Cache River at Patterson, AR,
showing effects of different recording methods


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This report should be cited as follows:

Nestler, J. M., and Long, K. S. (1994). “Cumulative
impact analysis of wetlands: Hydrologic indices,”
Technical Report WRP-SM-3, U.S. Army Engineer
Waterways Experiment Station, Vicksburg, MS.

The contents of this report are not to be used for advertising, publication, or
promotional purposes. Citation of trade names does not constitute an official
endorsement or approval of the use of such commercial products.

vii


14

compared with the other decades. The range of RMSE is from ~100 cfs in
the 1961-70 decade to over 3,000 cfs in the decade of 1941-50. .

Throughout the decades considered in the analysis of the Eleven Point
River, all RMSE intervals had roughly equivalent trends. The highest val-
ues for each RMSE interval was found in the 1941-50 decade, with the
lowest in 1931-40.

The time-scale analysis of the Little Red River flows shown in Figure 17
reveals the decade in which the river was impounded, with resulting
stabilization of flows. Each time period for which the root-mean-square
error was calculated (3-day periods to 2-month periods) reflected marked
damping of flow fluctuation. All flows were considered in the analysis in
order to detect and to demonstrate the abrupt change wrought by regula-
tion, whereas time-scale analysis of the Cache River at Patterson (Figure 16)
was restricted to flows less than 200 cfs in an attempt to discern suspected
changes to base flow conditions. When all flows are considered for the
Cache River at Patterson as for the other three streams (Figure 17), the
RMSE intervals from decade to decade are essentially flat, with RMSE1
less than 200 cfs, and RMSES greater than 1,200 cfs. This pattern offers
sharp contrast to the Cache River at Patterson analyzed with only flows
less than 200 cfs.

Chapter 2. Methods and Results


1921-40

‘
Sa a
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3 a4 gt

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dale > ° “

g a

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1 1

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+1 2 8 4 § 6 7 8 8 OM  W 1 2 8 4 6 6 7 8 9 0 1 12

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9

1981-88
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Month Month

Figure 12. Harmonic analysis of the Cache River at Patterson, AR


1941-50 1971-80

‘ Benn, o o o
= a ;
; ce a? ook
u a4 ss e ‘
H a tase i
H Nee i :
re ey ont zs + s 6 7 . 9 oO MW B
a oe

Figure 13. Harmonic analysis of the Buffalo River near St. Joe, AR


MISSOURI
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Figure 1. Cache River Study area


teal

US Army Corps

of Engineers
Waterways Experiment = Loa 7 N
rt
Station .
‘TECHNOLOGY

hey ‘ FOR FORRUATION CONTACT
2RORNMENTAL \g PUBLIC AFFAIRS OFFICE
LABORATORY H U.S. ARMY ENGINEER
\ WATERWAYS EXPERIMENT STATION
1000 HALLS FERAY ROAD

STRUCTURES
o UABORATORY
oe
0 ° oom

Waterways Experiment Station Cataloging-in-Publication Data

Nestler, John M.

Cumulative impact analysis of wetlands : hydrologic indices / by John
M. Nestler, Katherine S. Long ; prepared for U.S. Army Corps of Engineers.

45 p. : ill. ; 28 cm. — (Technical report ; WRP-SM-3) (Wetlands.

Research Program technical report : WRP-SM-3)

Includes bibliographic references.

1. Wetlands — Environmental aspects. 2. Hydrology — White River
(Ark. and Mo.) 3. Stream measurements — Illinois — Cache River.
4. Hydrologic cycle. |. Long, Katherine S. I. United States. Army. Corps
of Engineers. Ill. U.S. Army Engineer Waterways Experiment Station.
IV. Wetlands Research Program (U.S.) V. Title. VI. Title: Hydrologic
indices. VII. Series: Technical report (U.S. Army Engineer Waterways
Experiment Station) ; WRP-SM-3. VIII. Series: Wetlands Research
Program technical report ; WRP-SM-3.
TA7 W34 no.WRP-SM-3



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Cumulative Impact Analysis of Wetlands: Hydrologic Indices

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Available from National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161.

12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release; distribution is unlimited.

13. ABSTRACT (Maximum 200 words)

In order to make informed decisions concerning cumulative impact analysis of wetlands, the Corps of
Engineers Districts and other wetlands professionals need data often not directly available. Cumulative im-
pact assessment of wetlands includes relating historic patterns of flow, derived from the stream’s flow re-
cord, to changes in the watershed associated with that stream. Harmonic analysis and time-scale analysis
were applied to selected stream records to ascertain their potential for describing cumulative impacts.

The study area chosen included selected streams in the White River basin, Arkansas/Missouri. The
Cache River received particular emphasis because a significant amount of information was readily available

: concerning it and its surroundings. Daily flow values were retrieved from each of the streams. Using non-
linear, harmonic analysis as well as time-scale analysis (a technique adapted from fractal geometry) to re-
veal the time-dependent patterns in the respective samples, the results were compared decade-by-decade to
discern changes in the historic, seasonal patterns. Other streams in the White River basin were analyzed in the
same manner and compared with the Cache River, noting historic changes in land use and stream regulation.

. (Continued)
14, SUBJECT TERMS 15. NUMBER OF PAGES
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Cumulative Impact Analysis of Wetlands: Hydrologic Indices

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'6. AUTHOR(S)
John M. Nestler, Katherine S. Long

. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Army Engineer Waterways Experiment Station
3909 Halls Ferry Road
Vicksburg, MS 39180-6199

8. PERFORMING ORGANIZATION
REPORT NUMBER

Technical Report
WRP-SM-3

g }. SPONSORING/ MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Army Corps of Engineers
Washington, DC 20314-1000

10. SPONSORING / MONITORING
AGENCY REPORT NUMBER

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Available from National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161.

j2a. DISTRIBUTION / AVAILABILITY STATEMENT
Approved for public release; distribution is unlimited.

12b, DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The study area chosen included selected streams in the White River

same manner and compared with the Cache River, noting historic changes

In order to make informed decisions concerning cumulative impact analysis of wetlands, the Corps of
Engineers Districts and other wetlands professionals need data often not directly available. Cumulative im-
pact assessment of wetlands includes relating historic patterns of flow, derived from the stream’s flow re-
cord, to changes in the watershed associated with that stream. Harmonic analysis and time-scale analysis
were applied to selected stream records to ascertain their potential for describing cumulative impacts.

Cache River received particular emphasis because a significant amount of information was readily available
i concerning it and its surroundings. Daily flow values were retrieved from each of the streams. Using non-
linear, harmonic analysis as well as time-scale analysis (a technique adapted from fractal geometry) to re-

veal the time-dependent patterns in the respective samples, the results were compared decade-by-decade to

discern changes in the historic, seasonal patterns. Other streams in the White River basin were analyzed in the

basin, Arkansas/Missouri. The

in land use and stream regulation.

(Continued)

SUBJECT TERMS

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15. NUMBER OF PAGES
45

16. PRICE CODE

+] 18. SECURITY CLASSIFICATION
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Prescribed by ANSI Std. 239-18


Harmonic analysis. Harmonic analysis evaluates the fit of a time series
of data to a harmonic (usually cosine or sine) function. Harmonic analysis
typically generates four coefficients—mean, period, phase, and amplitude—
that can be used to describe a process that approximates a harmonic func-
tion. Each of the coefficients provides reasonably well-defined information
about complex hydrologic time series (Trost 1991). These coefficients
can be used singly or in various combinations to describe hydrologic pat-
terns. For example, the mean provides information about the central ten-
dency of the pattern; the phase (usually expressed as an angle in radians)
provides information about the seasonality of the discharge pattern, and
the amplitude provides information on the range of hydrologic conditions
to be expected over a single period (usually 1 year).

The underlying pattern in monthly discharges at different streams can
be explored and summarized using harmonic analysis of log-transformed
mean monthly discharge data when the underlying annual discharge pat-
tern of the river system approximates a cosine function (with period = 1
year). Log-transformed data are more meaningful surrogates of habitat
quality than untransformed data (i.e., gauged discharge data) because both
water depth and water velocity in streams can usually be expressed as sim-
ple power functions of discharge at a given cross section. Thus, stage
changes in wetlands over long time periods can be inferred by harmonic
analysis, even when stage information (water surface elevation) may not
be available directly.

Harmonic analyses of the Cache River gauge data were based on
stream gauging records as displayed in “National Water Conditions” pub-
‘lished by the U.S. Geological Survey. Patterns in mean (minimum, maxi-
mum) monthly discharges at 10-year (and 5-year) intervals were evaluated
by fitting them to a cosine function employing nonlinear regression (SAS
Institute, Inc. 1988) using

LMEANQ;, = AMP x cos[(MONTH + PHS) x PER x pi]

where
LMEANQ = log-transformed mean (minimum, maximum) monthly
discharge (standardized to a mean of 0.0)
AMP = amplitude
MONTH = coded such that 0.0 < MONTH < 1.0
PHS = phase
PER = period

The above procedure was applied to weekly mean discharges as well.
For each gauge location, harmonic analysis allows one to infer the prob-

able dominant hydrologic factors (e.g., groundwater, winter rain, and
snowmelt) that determine hydrologic patterns by evaluating the values of

Chapter 2 Methods and Results


Table 1
Pearson Correlation Coefficient Values for Flow Parameters of

Selected Area Streams

Pearson Correlation Coefficients Log-Transformed Discharge, cfs

Weekly Monthly

Minimum Minimum
Mean to to Mean to Mean to to Mean to
Decade Minimum =| Maximum | Maximum | Minimum | Maximum -| Maximum

Buffalo River near St. Joe, AR

1941-50 0.84" 0.92" 0.65" 0.93" 0.92" 0.80°
1951-60 0.88" 0.96" 0.77" 0.92" 0.96° 0.86"
1961-70 0.74* 0.95° 0.57" 0.77" 0.97* 0.69*
1971-80 0.79" 0.95" -0.66" 0.84" 0.99* 0.80"
1981-90 0.68" 0.96" 0.54* 0.69* 0.92* 0.46

Eleven Point River near Bardley, MO

1941-50 0.62" 0.92" 0.48" 0.66 . 0.93" 0.65
1951-60 0.76" 0.91" 0.56" 0.83" 0.93" 0.68"
1961-70 0.60* 0.88" 0.31 0.74" 0.88* 0.51
1971-80 0.61" 0.93" 0.52" 0.68" 0.94° 0.59
1981-90 0.28 0.91* 0.10 0.24 0.93" 0.03

Little Red River near Heber Springs, AR

1921-30 0.84" 0.99° 0.76" 0.94" 0.99" 0.91"
1931-40 0.87" 0.98" 0.81" 0.90" 0.98" 0.87"
1941-50 0.72" 0.93" 0.54" 0.66 0,92" 0.56
1951-60 071° 0.96" 0.56" 0.77* 0.95" 0.50
1961-70 071° 0.95" 0.60° 0.83" 0.97" 0.76*
1971-80 0.20 0.89" 0.05 0.01 0.90° 0.03
1981-90 0.48" 0.97" 0.25 0.27 0.92* 0.13

Cache River at Patterson, AR

1921-40 0.77" 0.96" 0.62" 0.86" 0.93" 0.64
1941-50 0.78" 0.92* 0.66" 0.78* 0.91" 0.75*
1951-60 0.67" 0.96" 0.55 0.76" 0.96" 0.63
1961-70 0.36 0.93* 0.25 0.31 0.93* 0.25
1971-80 0.39 0.86" 0.11 0.41 0.89* 0.17
1981-90 0.00 0.87" 0.34 0.09 0.89" 0.22

Note: * means P = <0.02.

The Eleven Point River near Bardley, MO (Figure 14), exhibits a mini-
mum mean discharge of small amplitude, not varying with the mean and
maximum except for the decades of 1951-60 and 1961-70, in which the
minimum seem to be in phase with the mean and maximum. The minimum
again appears to be out of phase in the decades of 1971-80 and 1981-90.
In all decades, however, the fluctuation of the minimum throughout all
months is limited.

In the case of the Little Red River (Figure 15), only four decades (1931-
1990) should be considered since the record of the decade of 1921-30 did

Chapter 2 Methods and Results


Wetlands Research Program Technical Report WRP-SM-3
September 1994

Cumulative Impact Analysis of Wetlands
Using Hydrologic Indices

by John M. Nestler, Katherine S. Long

U.S. Army Corps of Engineers
Waterways Experiment Station
3909 Halls Ferry Road
Vicksburg, MS 39180-6199

Final report
Approved for public release; distribution is unlimited

Prepared for U.S. Army Corps of Engineers
Washington, DC 20314-1000


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18

Croonquist, M. J., and Brooks, R. P. (1991). “Use of avian and mammalian
guilds as indicators of cumulative impacts in riparian-wetland areas,”
Environmental Management 15(5), 701-714.

Davies, K. (1991). “Cumulative environmental effects: A compendium,
Ecosystems Consulting Inc., Orleans, Ontario. For Federal Environ-
mental Assessment Review Office. (First Draft).

Ehrenfeld, J. G., and Schneider, J. P. (1991). “Chamaecyparis thyoides
wetlands and suburbanization: Effects on hydrology, water quality and
plant community composition,” Journal of Applied Ecology 28, 467-
490.

Gehrels, J., and Mulamoottil, G. (1990). “Hydrologic processes in a
southern Ontario wetland,” Hydrobiologia 208, 221-234.

Gosselink, J. G., Sasser, C. E., Creasman, L. A., Hamilton, S. C., Swen-
son, E. M., and Shaffer, G. P. (1990). “Cumulative impact assessment
in the Pearl River Basin, Mississippi and Louisiana,” LSU-CEI-90-03,
Louisiana State University, Baton Rouge, LA.

Granholm, S., Kelly, P., Miller, K., and Sorenson, P. (1988). “Cumula-
tive impacts on seasonal wetlands in the South and Central San Fran-
cisco Bay Area.” Proceedings of the National Wetland Symposium,
Urban Wetlands. Association of Wetland Managers, Inc., Omnipress,
Madison WI, 56-64.

Gustard, A., and Wesselink, A.J. (1993). “Impact of land-use change on
water resources: Balquhidder Catchments,” Journal of Hydrology 145,
389-401.

Kleiss, B. A. (1993). “Cache River, Arkansas: Studying a bottomland
hardwood (BLH) wetland ecosystem.” The Wetlands Research Pro-
gram Bulletin, 3 (1), U.S. Army Engineer Waterways Experiment Sta-
tion, Vicksburg, MS.

Leibowitz, S. G., Preston, E. M., Arnaut, L. Y., Detenbeck, N. E., Hagley,
C. A., Kentula, M. E., Olson, R. K., Sanville, W. D., and Sumner, R. R.
(1992). “Wetlands Research Plan FY 1992-1996: An integrated risk-
based approach.” EPA/600/R-92/060, U.S. Environmental Protection
Agency, Environmental Research Laboratory, Corvallis, OR.

Lloyd, J. W., Tellam, J. H., Rukin, N., and Lerner, D. N. (1993). “Wet-
lands vulnerability in East Anglia: A possible conceptual framework
and generalized approach,” Journal of Environmental Management 37,
87-102.

Nestler, J. M. (1993). “Instream flow incremental methodology: A syn-
opsis with recommendations for use and suggestions for future research,”


‘The following two letters used as part of the number designating technical reports of research published
under the Wetlands Research Program identify the area under which the report was prepared:

Task Task
cp Critical Processes RE Restoration & Establishment
DE Delineation & Evaluation SM Stewardship & Management

The contents of this report are not to be used for advertising,
publication, or promotional purposes. Citation of trade names
does not constitute an official endorsement or approval of the use
of such commercial products.

CAA
a PRINTED ON RECYCLED PAPER


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Simple indices and summary variables

These indices, defined in hydrology textbooks, describe measures of
central tendency and dispersion. They provide a relatively low-resolution
description or summary of complex hydrologic patterns. These indices are at-
tractive primarily because of their intuitive simplicity, but they usually are
not sensitive enough to reveal the sometimes subtle shifts in hydrologic
patterns that often must be described when assessing cumulative impacts.
Figure 2 shows the mean, maximum, and minimum annual flows for the
Cache River at Patterson, AR, followed by corresponding values for the
Buffalo River, the Eleven Point River, and the Little Red River (Figure 3).
Annual summary statistics cannot describe time-dependent discharge
changes critical to many wetland processes.

Mean annual discharge. Mean annual discharge (expressed as volume
per unit time) is defined as the average of individual daily mean dis-
charges (for 1 year) at a specific location on a river. This variable.is com-
monly used to summarize the magnitude of discharge in a river; its
applicability to assess impact is limited because the mean is heavily influ-
enced by high discharge events that can mask effects of wetland alter-
ations. Effects of impacts on wetlands that disrupt critical low discharge
patterns are not usually well-described by this variable.

Median annual discharge. Median annual discharge is defined as the
average daily discharge that is exceeded 50 percent of the time at a spe-
cific river location over a long period of record. Median annual discharge
is less influenced by high discharge events and is, therefore, better for
summarizing discharge patterns than is the mean annual discharge.

Mean/median monthly discharges. Mean/median monthly discharges
are the mean/median of daily discharges by month. Mean or median
monthly discharges can sometimes depict the effects of wetland alterations
on system hydrology during the dry season. However, describing long-
term effects of a wetland alteration in terms of changes in monthly median
flows often is inadequate because such analyses may not accurately detect
or adequately describe changes in patterns between months, particularly if
lower flows are assessed. Figure 4 presents decade-by-decade median
monthly flows for the Cache River. Note that pattern changes in median
flows between decades are difficult to detect. Succeeding figures show
each month as changes in median, mean, and maximum occurring decade-
by-decade.

Ranges of discharge. Ranges of discharge are used to describe the ex-
treme values that may be recorded by the stream gauge. Ranges are typi-
cally defined on a monthly, seasonal, or annual basis. Figure 5 shows
trends for each decade by month.

Discharge-duration curves. Discharge-duration curves give the duration

of occurrence of particular ranges of discharges in the river. Discharge-
duration curves are often a useful means of describing hydrologic patterns

_ Chapter 2 Methods and Results


the coefficients produced by the nonlinear regression. For example, a
“seasonality index,” the absolute value of the ratio of amplitude of mean
monthly discharges to mean of monthly discharges (assuming that the dis-
charges follow a sinusoidal pattern), can be used to estimate the degree of
seasonality in mean monthly discharges. This index has been defined here
such that low values of this ratio indicate that discharges occur randomly
(or in nonannual periods), whereas high values indicate that discharges
fall within distinct seasonal patterns. Western streams receiving substan-
tial amounts of snowmelt (e.g., Changnon, McKee, and Doesken 1991)
typically exhibit high seasonality indices (Nestler 1993).

Seasonality indices based on monthly mean flows (also minimum mean
monthly flows, maximum mean monthly flows, and median mean monthly
flows) for periods of record examined for the Cache River at Patterson and
the other rivers are compared in Figure 11. This analysis reveals that (a) the
Buffalo and the Eleven Point rivers exhibit little change in seasonality pat-
tern of mean and maximum over their respective periods of record; (b) the
Little Red River, under complete regulation by Greers Ferry Dam since
March of 1962, appears to take an abrupt plunge in the seasonality index
of the minimum mean in the decade beginning in 1961; (c) the Cache
River at Patterson exhibits an erratic trend in the seasonality. index of the
minimum; (d) the minima exhibit higher levels of seasonality for each of
the rivers examined except for the Eleven Point River, although this high
value is most pronounced in the Little Red River prior to impoundment in
the 1960s; and (e) the Eleven Point River showed least differences among
its means, minima, and maxima. From the analysis, these authors con-
clude that hydrological processes in the Cache River basin that operate on
a monthly time scale have been altered to the extent that the seasonal dis-
charge pattern in the Cache River wetlands has been affected.

After the decade of the 1950s, the disruption in the seasonal pattern of
monthly minimum mean discharges is characterized by a reduction in the
lowest monthly mean discharges and a loss in the seasonal pattern of low
discharges evidenced by minimum means not following the general pattern

" of the means or the maximum means (see Table 1). Each decade shows
increased winter and spring discharge probably related to the effects of in-
creased winter and spring rainfall (Figure 4). The harmonic analysis for
the Cache River maxima, mean, and minima of monthly mean discharges
(Figure 12) indicates that a disruption in the pattern of the lowest of the
mean discharges occurred in the decade of the 1950s (the individual
points do not conform as closely to the curve of best fit).

A comparison of the harmonic patterns observed for the Cache River
with the other sites indicated that the patterns in the Cache River were
unique and could not be attributed to regional drought patterns or global
warming. The Buffalo River near St. Joe, AR (Figure 13), had monthly
mean discharges with minima, means, and maxima appearing to be in
phase for all decades examined (1941-90). Seemingly uncharacteristic
late year lows occurred in the decades of 1951-60 and 1961-70.

Chapter 2 Methods and Results