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A New Hydrological Regimen for the Atchafalaya River to Enhance Fisheries and Coastal Accretion

Authors:

Abstract

PROPOSAL: To increase the discharge to the Atchafalaya River during intermediate flow conditions No change in discharge is proposed under high-flow or low-flow conditions This modification from the current control strategy will divert a long term average additional flow of 48,000 cfs This represents a 20% increase in Atchafalaya River discharge and a 29% increase in diversion discharge over present conditions. BENEFITS OF PROPOSED INTERMEDIATE AUGMENTATION STRATEGY: Additional coastal land protection and accretion Increase basin .commercial and recreational fisheries production Increase length of season for access to basin resources Help maintain a "wet and wild" Atchafalaya Basin * These are slides from meeting presentation. Also see manuscript titled "A New Hydrological Regime for the Atchafalaya River to Enhance Fisheries and Coastal Accretion."
A New Hydrological Regime for the Atchafalaya River
to Enhance Fisheries and Coastal Accretion
C.
Frederick Bryan, Ph.D.
Leader and Professor Adjunct, Louisiana Cooperative Fish and Wildlife Research Unit,
National Biological Service, Louisiana State University
Michael Gene Waldon, Ph.D., P.E.
Associate Professor-Research, Center for Louisiana Inland Water Studies, Department of
Civil Engineering, University of Southwestern Louisiana
ACKNOWLEDGMENTS: Published and pre-publication discharge and stage data utilized
in this study were provided by the New Orleans District Office of the U.S. Army Corps
of
Engineers, and by the Louisiana District
of
the U.S. Geological Survey. Their
assistance and cooperation are gratefully acknowledged. Opinions and conclusions
expressed in this paper are solely those
of
the authors.
CR (Constant Ratio) Strategies: Maintain a constant ratio
of
daily discharge,
currently 70/30
The lA (Intermediate Augmentation) Strategy
PROPOSAL:
To increase the discharge to the Atchafalaya River during intermediate flow
conditions
No change in discharge is proposed under high-flow or low-flow conditions
This modification from the current control strategy will divert a long term average
additional flow
of
48,000 cfs
This represents a 20% increase in Atchafalaya River discharge and a 29% increase
in
diversion discharge over present conditions.
BENEFITS OF lA STRATEGY:
Additional coastal land protection and accretion
Increase basin .commercial and recreational fisheries production
Increase length
of
season for access to basin resources
Help maintain a "wet and wild" Atchafalaya Basin
.
MISSISSIPPI RIVER CONSTRAINTS:
Water supply/saltwater intrusion
Transportation
ATCHAFALAYA RIVER CONSTRAINTS:
Flooding near coast
Agriculture
Channel scour/effeciency
Sedimentation
.
.
s:
iii"
"'
"'
"'
"0.
"0
;u
<'"
(D
~
Qr=QA+QM
---
·--------
-----
OA
~
OM
s:
~
iii"
.,
"'
-
iii"
~
"'
~
"0
?'
""0
~.
;u
~
<'"
(D dl
~
~
Diagram
of
flows
in
the Mississippi and Atchafalaya Rivers.
600
~-~-----------~60%
500
50%
12
4bd
u
g
....
o 0
~300
0
40%""
~
f2
200
""
30%
100
0
20%
0
~
~
~ ~
1~1~1~1~
TOTAL
Q
(1000
CFS)
""
Present (CS-70/30) and proposed (lA) strategies for
Atcl1afal<iYa
River
discl19rge
and
disc::harge
ratio
..
500
,.....-:---.,.---,-----,----,.-----,
400
+----------------+----------------i---------------""i·''
...
·---"-·"·-l
~
·1'3<;;·
300
+--··------------+---------------+--.-~
~-o
.,g
E'm
;i
!200
+--------------·+--···-::
o,~----+-----~----~----~
0 5
10 15
20
Stage
at
Butte
La
Rose
(feet)
X
1987
1992
Discharge at Simmesport versus stage
at
Butte
La
Rose. Solid reference lines bracket
upper and lower limits for proposed
lA
discharge augmentation.
100%,--------------,-----,
90%
80%·-
""
70%
60%
-~
oo%L
20%
10%
0%
1 2
DAYS
+-~~-+--!~--~~~
3 4 5 6 7 8 9
10
11
12
MONTH
Percent increase in monthly average Atchafalaya River discharge, and average percent of
daysby
month with increased discharge to the Atchafalaya River.
2500
.--------------,
2000
E'
§
1500
TOTAL
t5
~
1000
~
500
0%
20%
40%
60%
80%
100%
PERCENTILE
Percent of time that discharge is exceeded for the Atchafalaya River (AR), Mississippi
River, and total discharge. Bothpresent CS-70/30 (thin line) and proposed
lA
(thick line)
values are shown.
500
,-----.---
.....
---,------,
400
+····---·----·
---;-----·--------··-r------··---------•-~""'--------··--1
0-r------+------,_------~----~
0 5
10
15
20
Sloge
al
Butte
lo
Rose
(feel)
X
1987
1992
Discharge at Simmesport versus stage at Butte
La
Rose. Solid reference lines bracket
upper and lower limits for proposed
lA
discharge augmentation.
Under the
lA
strategy, during intermediate discharges, diversion to the
Atchafalaya River will be augmented. Specifically, it
is
proposed that:
QA=0.30r
QA=0.30za+(QT-02a)
QA=0.30
80
QA=Q.3QT
QT<Oza,
0
20
<QT<(0.30
80
+0.
70
20
),
(0.30
80
+0.
70
20
)<0
1
<0
80
,
Or>Oaa,
Discharge
statistics
(1000
cfs).
TOTAL
CR-70/30
lA
(PRESENT)
(PROPOSED)
DISCHARGE
MISS
ATCH
MISS
ATCH
MEAN
790
553
237
504
285
MAX
2100
1470
630
1470
630
MIN
159
111
48
111
48
STD
430
301
129
315
131
.•
HARMONIC
560
392
168
348
196
MEAN
MEDIAN
717
502
215
364 353
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