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
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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
2.
Using an aerial photograph (not a topog. map), measure stream length and related valley length for at least two meander wavelengths; then divide:
1.
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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