1. 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 Cordova
June 12, 2008

2. 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.

3. 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.

4. Introduction
Rincon Creek

5. Objective
To develop a stage-discharge rating using the Continuous Slope-Area (CSA) method at the Babocomari and San Pedro River.

6. 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.

7. Theory
Water Surface Profile At Peak Discharge
Stage
Distance

8. 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.

9. 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.

10. Theory
Water Surface Profile At time = 0
Stage
Distance

11. Theory
Water Surface Profile At time = 1
Stage
Distance

12. Theory
Water Surface Profile At time = 2
Stage
Distance

13. Theory
Water Surface Profile At Peak time = 3
Stage
Distance

14. Theory
Water Surface Profile At time = 4
Stage
Distance

15. Theory
Water Surface Profile At time = 5
Stage
Distance

16. 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.
Continuous slope-area site at lower
Babocomari River (.15 miles downstream of USGS Gaging Station )
Continuous slope-area site at lower
Babocomari River (.15 miles downstream of USGS Gaging Station )

17. Babocomari River
The existing gage ( ) 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.

18. Babocomari River

19. 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.

20. Babocomari River

21. Babocomari River CSG2 CSG1 CSG4 CSG3 CSG5 CSG6 CSG7 CSG8 X1 X2 X3 X4
4920
4940
4960
4980
5000
5020
5040
5060
5080
5100
5120
4900
4950
5050
5150
5200
5250
5300
EASTING, IN FEET
NORTHING, IN FEET
CSG2
CSG1
CSG4
CSG3
CSG5
CSG6
CSG7
CSG8 X1 X2 X3 X4

22. Babocomari River

23. Babocomari River
Since 2002, there have been five major flow events in the Babocomari River measured with the continuous slope-area method.

24. Babocomari River
Stage Hydrograph for 07/27/2006 Flow Event

25. Babocomari River
Discharge Hydrograph for 07/27/2006 Flow Event

26. Babocomari River Gage vs. CSA 07/27/2006 Flow Event Total Gage Volume
Total Continuous
Slope-Area Volume
3451 AF
-19 % Difference

27. Babocomari River
Rating based on the 07/27/2006 Flow Event (n = 235)

28. Babocomari River

29. Babocomari River

30. Babocomari River

31. Field Area 2 The San Pedro River

32. The San Pedro River One 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.

33. The San Pedro River One 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.

34. The San Pedro River

35. The San Pedro River CSG1 X1 X2 X3 CSG3 CSG2 61400 61420 61440 61460
61480
61500
61520
38620
38630
38640
38650
38660
38670
38680
38690
EASTING, IN FEET
NORTHING, IN FEET X1
CSG1
CSG2
CSG3 X2 X3

36. The San Pedro River Looking upstream from cross-
section three.
Looking downstream from cross-
section two.

37. The San Pedro River

38. The San Pedro River

39. The San Pedro River

40. The San Pedro River
Stage Hydrograph 07/27/2007 through 08/15/2007

41. The San Pedro River Total Gage Volume 14470 AF Total Continuous
Slope-Area Volume
16444 AF
14 % Difference

42. The San Pedro River

43. 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.

44. Future Work Incorporate LIDAR scans to monitor channel changes.
LIDAR = LIght Detection And Ranging
Accurate Scans up to 1 Km
Very high resolution

45. Future Work
LIDAR unit

46. Future Work
LIDAR Scan of the Santa Cruz River near Congress

47. Future Work
Install scour chains to measure scour/ deposition of channel sediments during a flow event.

48. Questions

51. THREE CROSS-SECTION CONTINUOUS SLOPE AREA
ALERT GAGE
WITH
PRESSURE
TRANSDUCER
THREE CROSS-SECTION CONTINUOUS SLOPE AREA

52. THREE CROSS-SECTION CONTINUOUS SLOPE-AREA
VEKOL WASH CONTINUOUS SLOPE-AREA
ALERT GAGE
WITH
PRESSURE
TRANSDUCER
THREE CROSS-SECTION CONTINUOUS SLOPE-AREA

53. THREE CROSS-SECTION CONTINUOUS SLOPE-AREA
SAN PEDRO CONTINUOUS SLOPE-AREA
USGS GAGE
THREE CROSS-SECTION CONTINUOUS SLOPE-AREA

54. THREE CROSS-SECTION CONTINUOUS SLOPE-AREA
SAN PEDRO CONTINUOUS SLOPE-AREA
MONITORING
WELL
THREE CROSS-SECTION CONTINUOUS SLOPE-AREA

55. CONTINUOUS SLOPE AREA REACH AT TIME ZEROX1 X2 X3
STAGE, IN FEET
DISTANCE DOWNSTREAM, IN FEET

56. CONTINUOUS SLOPE AREA REACH AT LATER TIMEX1 X2 X3
STAGE, IN FEET
DISTANCE DOWNSTREAM, IN FEET

57. Why Measure Peak Streamflow Indirectly?
Flashy Events
Remoteness of Sites
No Cableway or Bridge
Just too Hazardous

58. The Middle San Pedro Basin
The Continuous Slope Area
(CSA) method will be used for
identifying the spatial distribution
of recharge and discharge along
the 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 refined
water budget of the basin