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

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.

Theory Water Surface Profile At Peak Discharge Stage Distance

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.

Theory Water Surface Profile At time = 0 Stage Distance

Theory Water Surface Profile At time = 1 Stage Distance

Theory Water Surface Profile At time = 2 Stage Distance

Theory Water Surface Profile At Peak time = 3 Stage Distance

Theory Water Surface Profile At time = 4 Stage Distance

Theory Water Surface Profile At time = 5 Stage Distance

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 09471400) Continuous slope-area site at lower Babocomari River (.15 miles downstream of USGS Gaging Station 09471400)

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 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

Babocomari River

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

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

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

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

Babocomari River 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 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.

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.

The San Pedro River

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

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 Stage Hydrograph 07/27/2007 through 08/15/2007

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

The San Pedro River

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.

Questions jcordova@usgs.gv

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

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

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

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

CONTINUOUS SLOPE AREA REACH AT TIME ZERO X1 X2 X3 STAGE, IN FEET DISTANCE DOWNSTREAM, IN FEET

CONTINUOUS SLOPE AREA REACH AT LATER TIME X1 X2 X3 STAGE, IN FEET DISTANCE DOWNSTREAM, IN FEET

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 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