Stream Geometry and Sketch Map. Learn how to take an azimuth on a compass (phone apps can work well too). 3. Lay out a longitudinal tape using chaining pins (note, your stream bag

Stream Habitat Measurement Techniques Day 2: Field Day

Stream Geometry and Sketch Map

Stream Geometry and Sketch Map Overview

Example sketch map, Figure A-15.

Site Sketch Form

Geometry Instructions

Stream Geometry and Sketch Map The measured geometry and sketch map characterize and document the plan form of the stream study reach. The sketch map is very important and documents the plan form (overhead view) of the reach and the locations of cross‐section and measurement sites. As such, sketch maps are useful in reports. Plan form geometry may be best measured initially with recent, large‐scale aerial photographs. All measurements should represent the range (min, max) and average values for the geometry variables.

Day 1 (Monday)

Tasks

1. Review sketch map components, stream geometry measurements, and use an aerial photo to make a radius of curvature geometry measurement.

2. Learn how to take an azimuth on a compass (phone apps can work well too). 3. Lay out a longitudinal tape using chaining pins (note, your stream bag only has 10 chaining pins).

This action will measure the stream length. 4. Each person draws a simple sketch map that includes the

a. stream pattern with “stationing” (distance from upstream site boundary to features taken from longitudinal tape)

b. valley cross‐section c. valley axis in degrees (from azimuth reading on compass)

5. As a group of six, measure stream meander lengths 6. Break into two teams of three. Each team makes all geometry measurements and places the

data on the appropriate places of the sketch map and on the data form. a. Stream Length b. Valley Length c. Sinuosity = SL/VL d. Bankfull Width at a “riffle” (pin flag to pin flag) e. Radius of Curvature f. Arc Lengths g. Linear Wavelengths h. Stream Meander Lengths i. Belt Widths

7. Calculate bankfull ratios (e.g., Radius of Curvature/Bankfull Width)

Equipment

(6) Engineer’s scales

(6) Compasses

(10) Chaining pins

(4) 300’ Longpro tapes (2 for stream length, 2 for valley length)

(6) Clipboards

(6) Pencils

(2) 100’ steel tapes

(2) Pin flags

(2) Calculators


Sketch Map The sketch map documents the location of the study reach, cross-section and measurement sites in relation to the landscape and verifies that the plan form of the stream has not significantly changed since the aerial photograph was taken. A broad-level valley cross-section showing channel, floodplains and terrace features in relation to the plan view are included on the sketch map. Table A-7 lists the items necessary to include on the sketch map, and Figure A-20 is an example sketch map. Note: sometimes a sketch map can become very cluttered with important information that is difficult to read. Consider making two or more copies of the general sketch map and split up the information.

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 floodplain 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

Copyright © 2013 Wildland Hydrology



Figu

re A

-20.

Exa

mpl

e sk

etch

map

.


Geomorphic Map Symbols


Sinuosity (k) Sinuosity is the only plan-form parameter used in the initial delineation of stream types at Level II (Worksheet A-1). Sinuosity describes how the stream has adjusted its slope in relation to the slope of its valley and is quantitatively described as the ratio of stream length (SL) to valley length (VL) and also as the ratio of valley slope (Sval) to channel slope (S). The stream and valley lengths are measured from two common points in a direction that is parallel with the fall line of the valley (Figure A-21). Valley slope (Sval) is measured as the water surface elevation difference between the same bed features (e.g., riffle to riffle) along the fall line of the valley divided by the valley length between the selected bed features. A third method can also be used to estimate sinuosity for reaches less than 40 bankfull widths, described as the ratio of Stream Meander Length (Lm) to Linear Wavelength (λ).

Figure A-21. Sinuosity diagram.

Belt Width (Wblt) Belt width is the lateral distance (perpendicular to valley) between the outside edges of two meanders that occupy opposite sides of the valley (Figure A-22). Belt width is used as an index of the lateral containment or confinement of a stream when compared with the width of the channel. Meander Width Ratio (MWR) is the belt width divided by the bankfull width. Various meander width ratios by stream type are shown in Figure A-23.

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


1. Using an aerial photograph (not a topog. map), measure stream length and related valley length for

C

OR

2. Using measured slope ratios, ...divide:

B


Meander Width Ratio (MWR) by Stream Type Categories

Stream Type A D B & G F C E

Plan View

Cross- Section View

A D G F C E B

Average Values 1.5 1.1 3.7 5.3 11.4 24.2 Range 1 – 3 1 – 2 2 – 8 2 – 10 4 – 20 20 – 40

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

Stream Meander Length (Lm) Stream Meander Length is the channel distance between the apex of two sequential meanders (Figure A-24) . Meander length ratio is the stream meander length divided by the bankfull width (Lm / Wbkf).

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



Linear Wavelength ( λ ) Linear wavelength is the longitudinal distance parallel with the fall line of the valley between the apex of two sequential meanders (Figure A-25) and is negatively correlated with sinuosity. Linear wavelength is expressed as a ratio to the bankfull width ( λ / Wbkf).

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

Radius of Curvature (Rc) Radius of curvature is a measure of the “tightness” of an individual meander bend and is negatively correlated with sinuosity. Radius of curvature is measured from the outside of the bankfull channel to the intersection point of two lines that perpendicularly bisect the tangent lines of each curve departure point (Figure A-26). Measurements taken in compound pools vs. compound bends are shown in Figure A-27. Radius of curvature is expressed as a ratio to the bankfull channel width (Rc / Wbkf).

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

6 Copyright © 2013 Wildland Hydrology


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



Arc Length (AL) Arc Lengthis the distance along the outside bend from the point of curvature to the point of tangency (Figure A-28)

Figure A-28. Arc length measurements

Arc Length


AREA-SITE LOCATION....REACH MAP Stream: Reach: Drawn By: Date:



AREA-SITE LOCATION....REACH MAP Stream: Reach: Drawn By: Date:


Geo

metry M

easuremen

ts

Stream

nam

e/location: _

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Date: ___

____

____

__ Tea

m m

embers: ___

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Attribute

Mea

suremen

t 1

Mea

suremen

t 2

Mea

suremen

t 3

Mea

suremen

t 4

Mea

suremen

t 5

Ran

ge

Average

Radius of

Curvature

(Rc)

Arc Leng

th

(AL)

Line

ar

Wav

elen

gth

(λ)

Stream

Mea

nder

Leng

th

(Lm)

Belt Width

(Wblt)

Sinuosity

Stream

length =

Valley length

=

Sinuosity

=

Ban

kful R

atios

Stream

nam

e/location: _

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Date: ___

____

____

__ Tea

m m

embers: ___

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Ban

kful w

idth (W

bkf) in a riffle: ___

____

____

_

Attribute

# 1

# 2

# 3

# 4

# 5

Min

Max

Average

Rc/ W

bkf

λ/ W

bkf

Mea

nder

Leng

th Ratio

L m/ W

bkf

Mea

nder

Width Ratio

(Wblt/ W

bkf)

Rc

= radius of curvature

λ

= Linear wavelength

L m

= Stream

mean

der length

Wblt =

Belt width

Geo

metry M

easuremen

ts

Stream

nam

e/location: _

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Date: ___

____

____

__ Tea

m m

embers: ___

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Attribute

Mea

suremen

t 1

Mea

suremen

t 2

Mea

suremen

t 3

Mea

suremen

t 4

Mea

suremen

t 5

Ran

ge

Average

Radius of

Curvature

(Rc)

Arc Leng

th

(AL)

Line

ar

Wav

elen

gth

(λ)

Stream

Mea

nder

Leng

th

(Lm)

Belt Width

(Wblt)

Sinuosity

Stream

length =

Valley length

=

Sinuosity

=

Ban

kful R

atios

Stream

nam

e/location: _

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Date: ___

____

____

__ Tea

m m

embers: ___

____

____

____

____

____

____

____

____

____

____

____

____

____

____

Ban

kful w

idth (W

bkf) in a riffle: ___

____

____

_

Attribute

# 1

# 2

# 3

# 4

# 5

Min

Max

Average

Rc/ W

bkf

λ/ W

bkf

Mea

nder

Leng

th Ratio

L m/ W

bkf

Mea

nder

Width Ratio

(Wblt/ W

bkf)

Rc

= radius of curvature

λ

= Linear wavelength

L m

= Stream

mean

der length

Wblt =

Belt width

Documents

Stream Geometry and Sketch Map. Learn how to take an azimuth on a compass (phone apps can work well too). 3. Lay out a longitudinal tape using chaining pins (note, your stream bag