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Stream Habitat Measurement Techniques Day 2: Stream Survey

Stream Geometry and Sketch Map

Stream Geometry and Sketch Map Overview

Example sketch map, Figure A-15.

Site Sketch Form

Geometry Instructions

Copyright © 2013 Wildland Hydrology

Stream Habitat Measurement Techniques Day 2: Field Day

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Stream Geometry and Sketch MapThemeasuredgeometryandsketchmapcharacterizeanddocumenttheplanformofthestreamthroughthestudyreach.Sinuosity,beltwidth,streammeanderlength,linearwavelengthandradiusofcurvaturearemeasured.Plan-viewgeometryisbestmeasuredwithrecent,large-scaleaerialphotographs.Allmeasurementsshouldrepresenttherange(minimum,maximum)andaveragevaluesforthegeometryvariables.RecordallgeometryvaluesandratiosinWorksheet A-3.

Table A-7. List of minimum items to include on sketch map.

Sketch Map Items

• Stream name and location• Date• Surveyors• North arrow• Scale of map• Legend • Direction of streamflow• Benchmark locations• Floodplain boundaries• Terrace features• Vegetation

• Landmarks including trees, logs, rocks, debris, dams, etc.

• Valley cross-section (including flood-plain and terrace features)

• Cross-section locations• Longitudinal profile stationing• Pebble count locations or transects• Meander geometry measurements• Bar features and bar sample locations• Abandoned channels

Geometry Instructions1. Developfamiliarityofthedesignatedreachbywalkingtheentirelengthwhilelookingattheaerialphotograph(sometimesitisalsohelpfultoviewthereachfromahighpoint).

2. Observefloodplains,terraces,abandonedchannels,bedrockoutcropsandlaterallyconfininghillslopesorroads.

3. Drawthereachtoscale(Figure A-20).Makesuretonotecross-sectionlocations.Noteanychangesthathaveoccurredsincetheaerialphotographwastaken.

4. Usingtheaerialphotograph,measuresinuosity,beltwidth,streammeanderlength,linearwavelengthandradiusofcurvatureanddelineatethereachandcross-section.Reportthegeometrymeasurementsasranges(minimum,maximum,mean)andasratiostothebankfullwidth(e.g.,Rc /Wbkf).Fieldmeasureanyareaswherethechannelhasshiftedsubstantiallysincethedateoftheaerialphotograph.

5. RecordallgeometrydatainWorksheet A-3andonthesketchmap.

Sketch MapThesketchmapdocumentsthelocationofthestudyreach,cross-sectionandmeasurementsitesinrelationtothelandscapeandverifiesthattheplanformofthestreamhasnotsignificantlychangedsincetheaerialphotographwastaken.Abroad-levelvalleycross-sectionshowingchannel,floodplainsandterracefeaturesinrelationtotheplanviewareincludedonthesketchmap.Table A-7liststheitemsnecessarytoincludeonthesketchmap,andFigure A-20isanexamplesketchmap.



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Figu

re A

-20.

Exa

mpl

e sk

etch

map

.



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AREA-SITE LOCATION....REACH MAP

Drawn By: Date: Stream: Reach:



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Belt Width (Wblt)Belt widthisthelateraldistance(perpendiculartovalley)betweentheoutsideedgesoftwomeandersthatoccupyoppositesidesofthevalley(Figure A-22).Beltwidthisusedasanindexofthelateralcontainmentorconfinementofastreamwhencomparedwiththewidthofthechannel.Meander Width Ratio (MWR)isthebeltwidthdividedbythebankfullwidth.VariousmeanderwidthratiosbystreamtypeareshowninFigure A-23.

Figure A-22. Meander geometry diagram for Belt Width (Wblt) measurements.

Sinuosity (k)Sinuosityistheonlyplan-formparameterusedintheinitialdelineationofstreamtypesatLevelII(Worksheet A-1). Sinuosity describeshowthestreamhasadjusteditsslopeinrelationtotheslopeofitsvalleyandisquantitativelydescribedastheratioofstreamlength(SL)tovalleylength(VL)andalsoastheratioofvalleyslope(Sval) to channelslope(S).Thestreamandvalleylengthsaremeasuredfromtwocommonpointsinadirectionthatisparallelwiththefalllineofthevalley(Figure A-21).Valleyslope(Sval)ismeasuredasthewatersurfaceelevationdifferencebetweenthesamebedfeatures(e.g.,riffletoriffle)alongthefalllineofthevalleydividedbythevalleylengthbetweentheselectedbedfeatures.Athirdmethodcanalsobeusedtoestimatesinuosityforreacheslessthan40bankfullwidths,describedastheratioofStreamMeanderLength(Lm)toLinearWavelength(l).

To Calculate SINUOSITY

Valley Length

A

B

C

D

Valley Length: A B

Stream Length: C D

Sinuosity ( ) =k C DA B

RA

ST

ME

R AST ME

TN

H

LE G

TN

H

LE G

Using measured slope ratios,...divide:

Valley Slope by Stream Slope

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Using an aerial photograph (not a topog. map), measure stream length and related valley length for at least two meander wavelengths; then divide:

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Stream Length by Valley LengthOR

Figure A-21. Sinuosity diagram.



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Figure A-23. Meander Width Ratio (belt width/bankfull width) by stream type.

Stream Type

PlanView

Cross-Section

View

Average Values

Range

A D C

20 – 402 – 101 – 25.3 1.1

A D F C EB

G

4 – 202 – 81 – 324.2 11.4 3.7 1.5

EFB G&

Meander Width Ratio (MWR) by Stream Type Categories

Stream Meander Length (Lm)Stream Meander Lengthisthechanneldistancebetweentheapexoftwosequentialmeanders(Figure A-24) . Meander length ratioisthestreammeanderlengthdividedbythebankfullwidth(Lm /Wbkf).

Figure A-24. Meander geometry diagram for Stream Meander Length (Lm) measurements.



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Linear Wavelength ( l )Linear wavelengthisthelongitudinaldistanceparallelwiththefalllineofthevalleybetweentheapexoftwosequentialmeanders(Figure A-25)andisnegativelycorrelatedwithsinuosity.Linear wavelengthisexpressedasaratiotothebankfullwidth(l/Wbkf).

Figure A-25. Meander geometry diagram for Linear Wavelength (l) measurements.

Figure A-26. Meander geometry diagram for Radius of Curvature (Rc) measurements.

Radius of Curvature (Rc)Radius of curvatureisameasureofthe“tightness”ofanindividualmeanderbendandisnegativelycorrelatedwithsinuosity.Radiusofcurvatureismeasuredfromtheoutsideofthebankfullchanneltotheintersectionpointoftwolinesthatperpendicularlybisectthetangentlinesofeachcurvedeparturepoint(Figure A-26).Measurementstakenincompoundpoolsvs. compoundbendsareshowninFigure A-27.Radiusofcurvatureisexpressedasaratiotothebankfullchannelwidth(Rc /Wbkf).



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Figure A-27. Radius of Curvature (Rc) measurements in a compound pool vs. bend.



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