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Application of the Continuous Slope-Area Method for Determining Stream Discharge and
Development of Rating Curves in Ephemeral Channels
Navajo Nation Hydroclimate Measurement, Data Storage and Processing Workshop
Window Rock, Arizona
Jeff CordovaJune 12, 2008
Introduction
• The USGS typically develops rating curves and infers streamflow based on measurements of stage at one cross section.
• This method requires a large installation of equipment and may require significant manpower beyond the budget of USGS projects.
• Existing gaging stations may lack infrastructure to measure high flows.
Introduction• These streamgages can be significantly
damaged or completely destroyed during large events.
• New methods to measure streamflow with relatively inexpensive equipment and that are rapidly deployable are needed.
Introduction
Rincon Creek
Objective
• To develop a stage-discharge rating using the Continuous Slope-Area (CSA) method at the Babocomari and San Pedro River.
Theory
• The Slope Area-Method is commonly used to measure peak discharge indirectly.
• The Slope Area-Method indirectly measures peak discharge from high water marks and/or debris lines after the event.
TheoryWater Surface Profile At Peak Discharge
Distance
Sta
ge
Theory
• The water surface profile is input into the SAC program to compute the discharge between the reaches based on the fall between each cross section.
Theory
• Originally conceived in not too far from here.
• The Continuous Slope-Area (CSA) method applies the same principles as the standard Slope-Area Method but at multiple locations and times along a stream reach.
TheoryWater Surface Profile At time = 0
Distance
Sta
ge
TheoryWater Surface Profile At time = 1
Distance
Sta
ge
TheoryWater Surface Profile At time = 2
Distance
Sta
ge
TheoryWater Surface Profile At Peak time = 3
Distance
Sta
ge
TheoryWater Surface Profile At time = 4
Distance
Sta
ge
TheoryWater Surface Profile At time = 5
Distance
Sta
ge
Field Area 1
• The Babocomari River is a tributary into the San Pedro River.
• The Babocomari River is mostly an ephemeral stream with some perennial reaches.
• Summer monsoon storms can cause significant streamflow.
Babocomari River
• The existing gage (09471400) is best suited for low to medium wading measurements.
• There is no cableway at the gage.
• An off road vehicle is needed to access the site.
Babocomari River
Babocomari River
• In July 2002, a CSA gage was constructed approximately .15 miles downstream of the gaging station.
• The CSA gage consists of eight crest-stage gages (CSG) installed on the left and right banks of four cross sections.
Babocomari River
Babocomari River
4920
4940
4960
4980
5000
5020
5040
5060
5080
5100
5120
4900 4950 5000 5050 5100 5150 5200 5250 5300
EASTING, IN FEET
NO
RT
HIN
G, I
N F
EE
T
CSG2
CSG1
CSG4
CSG3CSG5
CSG6
CSG7
CSG8X1
X2X3
X4
Babocomari River
Babocomari River
0
2000
4000
6000
8000
10000
12000
7/25
/02
10/25
/02
1/25
/03
4/25
/03
7/25
/03
10/25
/03
1/25
/04
4/25
/04
7/25
/04
10/25
/04
1/25
/05
4/25
/05
7/25
/05
10/25
/05
1/25
/06
4/25
/06
7/25
/06
DATE
DIS
CH
AR
GE
, IN
CF
S
• Since 2002, there have been five major flow events in the Babocomari River measured with the continuous slope-area method.
Babocomari River
40.00
42.00
44.00
46.00
48.00
50.00
52.00
54.00
56.00
58.00
7/26
/06 19
:12
7/27
/06 0:
00
7/27
/06 4:
48
7/27
/06 9:
36
7/27
/06 14
:24
7/27
/06 19
:12
7/28
/06 0:
00
TIME
ST
AG
E A
BO
VE
DA
TU
M,
IN F
EE
T
CSG1
CSG5
CSG7
Stage Hydrograph for 07/27/2006 Flow Event
Babocomari River
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
7/26
/06
19:1
2
7/27
/06
0:00
7/27
/06
4:48
7/27
/06
9:36
7/27
/06
14:2
4
7/27
/06
19:1
2
7/28
/06
0:00
TIME
DIS
CH
AR
GE
, C
FS
X1-X4
Discharge Hydrograph for 07/27/2006 Flow Event
Babocomari River
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
7/26
/06 19
:12
7/27
/06 0:
00
7/27
/06 4:
48
7/27
/06 9:
36
7/27
/06 14
:24
7/27
/06 19
:12
7/28
/06 0:
00
7/28
/06 4:
48
TIME
DIS
CH
AR
GE
, C
FS
X1-X4
9471400
Total Gage Volume4261 AF
Total ContinuousSlope-Area Volume3451 AF
-19 % Difference
Gage vs. CSA 07/27/2006 Flow Event
Babocomari River
40.00
42.00
44.00
46.00
48.00
50.00
52.00
54.00
56.00
58.00
0 2000 4000 6000 8000 10000 12000
DISCHARGE, IN CFS
EL
EV
AT
ION
AB
OV
E D
AT
UM
, IN
FE
ET
Rating based on the 07/27/2006 Flow Event (n = 235)
Babocomari River
Babocomari River
Babocomari River
Field Area 2 The San Pedro River
The San Pedro RiverOne CSA gage was installed consisting of three CSGs.
Each CSG consists of• Five feet of channel iron• One six foot t post• CSG brackets and pipe• One Pressure Transducer• Cemented into channel
One CSG per cross section.
The San Pedro RiverOne CSA gage was installed consisting of three CSGs.
Each CSG consists of• Five feet of channel iron• One six foot t post• CSG brackets and pipe• One Pressure Transducer• Cemented into channel
One CSG per cross section.
The San Pedro River
The San Pedro River
61400
61420
61440
61460
61480
61500
61520
38620 38630 38640 38650 38660 38670 38680 38690
EASTING, IN FEET
NO
RT
HIN
G, I
N F
EE
T
X1CSG1
CSG2
CSG3
X2
X3
The San Pedro River
Looking upstream from cross-section three.
Looking downstream from cross-section two.
The San Pedro River
The San Pedro River
The San Pedro River
The San Pedro River
42.00
44.00
46.00
48.00
50.00
52.00
54.00
7/27/2007 0:00 8/1/2007 0:00 8/6/2007 0:00 8/11/2007 0:00 8/16/2007 0:00TIME
ST
AG
E A
BO
VE
DA
TU
M,
IN F
EE
T
TL1
TL2
TL3
Stage Hydrograph 07/27/2007 through 08/15/2007
The San Pedro River
0
500
1000
1500
2000
2500
3000
3500
4000
7/27/2007 0:00 8/1/2007 0:00 8/6/2007 0:00 8/11/2007 0:00 8/16/2007 0:00
TIME
DIS
CH
AR
GE
, CF
S
X1X3
9471800
Total Gage Volume14470 AF
Total ContinuousSlope-Area Volume16444 AF
14 % Difference
The San Pedro River
40.00
42.00
44.00
46.00
48.00
50.00
52.00
54.00
0 500 1000 1500 2000 2500 3000 3500
DISCHARGE, IN CFS
EL
EV
AT
ION
AB
OV
E D
AT
UM
, IN
FE
ET
Conclusions
• The CSA method can be used to develop rating curves in ephemeral streams.
• The volume comparisons showed that the gage and CSA volumes were within 20 percent.
• The CSA method can be applied to all ranges of flow.
• The CSA method can supplement existing streamflow gages.
Future Work
• Incorporate LIDAR scans to monitor channel changes.
• LIDAR = LIght Detection And Ranging
• Accurate Scans up to 1 Km
• Very high resolution
Future Work
LIDAR unit
Future Work
LIDAR Scan of the Santa Cruz River near Congress
Future Work
• Install scour chains to measure scour/ deposition of channel sediments during a flow event.
ALERT GAGEWITH
PRESSURE TRANSDUCER
THREE CROSS-
SECTION CONTINUOUS SLOPE AREA
ALERT GAGEWITH
PRESSURE TRANSDUCER
THREE CROSS-SECTION
CONTINUOUS SLOPE-AREA
VEKOL WASH CONTINUOUS SLOPE-AREA
USGS GAGE
THREE CROSS-SECTION
CONTINUOUS SLOPE-AREA
SAN PEDRO CONTINUOUS SLOPE-AREA
THREE CROSS-SECTION
CONTINUOUS SLOPE-AREA
SAN PEDRO CONTINUOUS SLOPE-AREA
MONITORING WELL
ST
AG
E,
IN F
EE
T
DISTANCE DOWNSTREAM, IN FEET
X1 X2 X3
CONTINUOUS SLOPE AREA REACH AT TIME ZERO
ST
AG
E,
IN F
EE
T
DISTANCE DOWNSTREAM, IN FEET
X1 X2 X3
CONTINUOUS SLOPE AREA REACH AT LATER TIME
Why Measure Peak Streamflow Indirectly?
• Flashy Events
• Remoteness of Sites
• No Cableway or Bridge
• Just too Hazardous
The Middle San Pedro Basin
The Continuous Slope Area (CSA) method will be used foridentifying the spatial distribution of recharge and discharge alongthe San Pedro River
• Measure stage of the river to infer streamflow rate
• Monitor progression and duration of flows along channel reaches
Ultimately leading to a refinedwater budget of the basin
