channel cross-section methods

Channel Cross-section MethodsPurpose/Objective: Channel cross-sections provide useful information on the 3D development and geomorphological changes to tidal channels over time. A line is stretched from bankfull to bankfull perpendicular to the channel flow, and depths from the line to the channel bottom are measured every 0.5 meters along the line. Measurements can also be made with a laser level (Hood 2010, Roegner et al. 2008) or with an RTK GPS.

August 2009 March 2010

Photos by Jesse Barham

Field MethodsEquipment Needed:2 – 4 to 5 foot lengths

of 1.5“ PVCRubber Mallet or

Hammer2 – Wooden stake

FlaggingLong line

Torpedo line levelerMeasuring TapeMeasuring Stick

Data BookGPS

WadersIf needed: boat and life

vestsLaser level (optional)RTK GPS (optional)

XS West Marker XS East Marker

Tl. Channel width5 m to Endpoint Marker

Field Methods – Determine bankfull of channel and add 5 meters to each side

Field Methods – install endpoint markers

Field Methods – stretch level line and measuring tape across channel

XS West Marker XS East MarkerLevel Line

Field Methods – measure distance from channel bed to level line every 0.5 meters

XS West Marker XS East MarkerLevel Line

Measure distance from level line to channel bed

Field Methods – measure total width of channel

XS West Marker XS East Marker

Tl. Channel width

Field Methods – survey top of each endpoint marker so data can be converted to elevation

Field Methods Option 2. - measure channel cross-section using laser level (Hood 2010, Roegner et al. 2008)

Photo from Roegner et al. 2008

Field Methods Option 3. - measure channel cross-section with RTK GPS

1.1

1.3

1.5

1.7

1.9

2.1

2.3

522225 522230 522235 522240 522245 522250

Elev

atio

n (m

) NA

VD88

UTM Easting

Unit 3 North

Elevation (m) 2009 Elevation (m) 2010 Elevation (m) 2011

Data Entry and Analysis:Channel development (i.e. scour or fill) is determined by comparing measurements at channel cross sections over time.

References:Hood W. G. 2010. Tidal channel meander formation by depositional rather than erosional processes: examples from the prograding Skagit River Delta. Earth Surface Processes and Landforms 35: 319 – 330.

Roegner, G.C., H.L. Diefenderfer, A.B. Borde, R.M. Thom, E.M. Dawley, A.H. Whiting, S.A. Zimmerman, and G.E. Johnson. 2008. Protocols for Monitoring Habitat Restoration Projects in the Lower Columbia River and Estuary. PNNL-15793. Report by Pacific Northwest National Laboratory, National Marine Fisheries Service, and Columbia River Estuary Study Taskforce submitted to the U.S. Army Corps of Engineers, Portland District, Portland, Oregon.

For a detailed, pdf version of these methods, use the links on the right to download the Channel Cross-section SOP , Datasheet and Database Template.