bank erosion hazard index (behi)

8/17/2019 Bank Erosion Hazard Index (Behi)

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STANDARD OPERATING PROCEDURE

ASSESSING BANK EROSION POTENTIAL USING ROSGEN’S BANK

EROSION HAZARD INDEX (BEHI)

1.0 Overview

While stream bank erosion is a natural process that occurs in every watershed, excessiveerosion has serious adverse consequences for the physical and biological function of

rivers. Eroding stream banks can be a major source of sediment to a stream (up to !"

of the annual load# $imon and %horne, &''), and human activities such as urbani*ation

or dam construction can accelerate bank erosion rates by more than an order ofmagnitude. +t is often difficult, however, to distinguish between stream banks that are

eroding at a natural rate from those that are or have the potential to erode at unnaturally

high rates due to altered watershed hydrology or sediment loads. %he ank Erosion

-a*ard +ndex (E-+), created by ave /osgen of Wildland -ydrology, +nc. (/osgen,0!!&), is one of several procedures for assessing stream bank erosion condition and

potential. +t assigns point values to several aspects of bank condition and provides anoverall score that can be used to inventory stream bank condition over large areas,

prioriti*e eroding banks for remedial actions, etc. %his standard operating procedure

($12) describes two versions of the E-+ technique.

.0 Pr!"e#$re

elow are descriptions of two E-+ procedures. %he first describes the complete E-+ procedure created by /osgen, including identification of bankfull width. %he second

describes a modified E-+ procedure, which does not require identification of bankfullwidth. %he modified E-+ procedure is intended for use by workers who lackexperience in identifying bankfull indicators, including volunteer monitors. 3orrectly

identifying appropriate bankfull indicators requires considerable experience, and is the

most subjective step in the original E-+ procedure.

+n truth, both procedures described below are 4modified5, in that the step of calculating

E-+ scores has been simplified such that there is only a single score for each metric,

rather than the range of possible scores provided in /osgen5s original paper. %hissimplification is intended to remove some unnecessary subjectivity from the field

observations, without overly reducing the utility of the procedure.

A. C!%&'ee BEHI Pr!"e#$re

%he complete E-+ procedure consists of five metrics# four observational and onerequiring some measurements. %hey are6

&. /atio of bank height to bankfull height

0. /atio of root depth to bank height

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9. /oot density, in percent

and not make

> the observations.

/atio of bank height to bankfull height. %his is the most challenging of the E-+

metrics, as it requires accurate identification of bankfull indicators. ? full discussion of

different bankfull indicators is beyond the scope of this $12, but it is thoroughly

discussed in Williams (&';), and a useful free video is available from the @.$. Aorest$ervice (0!!9). 3ommon bankfull indicators in stable southern Bichigan streams

include top of bank, top of point bars, and other changes in channel slope. =egetativeindicators are seldom useful in southern Bichigan streams. ankfull indicators in

unstable streams (i.e., incising or aggrading streams) can be more difficult to identify, but

are usually less than top of bank.

/atio of root depth to bank height. /oot depth is the ratio of the average plant root depth

to the bank height, expressed as a percent (e.g., roots extending 05 into a


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i*$re 1. Si%&'e +,# -!re E&e,/ive ( 100) I,"'i,!%eer/

B. -!#i2ie# BEHI Pr!"e#$re

+f the field staff lack experience with identifying bank full indicators, it is recommended

that the bank height7bankfull height ratio metric be dropped from the E-+ calculation,

leaving four metrics6

&. /atio of root depth to bank height

0. /oot density, in percent

9. $urface protection, in percent


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T+4'e 1. S"!re/ 2!r 5e C!%&'ee BEHI.

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i*$re . BEHI S"!re E+%&'e

stream

reaches in portions of the same watershed, or an adjacent watershed, that are believed to be (relatively) undisturbed by urban development, stream channeli*ation, etc. ? good

document describing how to choose and document conditions at a reference site is the@.$. Aorest $ervice report by -arrelson, et al. (&''


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( even in geomorphically stable streams.

• $tream banks in 4high traffic5 areas (parks, livestock crossings, etc.) are

not representative of average conditions and should be avoided > unless

they are the specific focus of the study.

While volunteers can collect large amounts of useful E-+ data with adequate training

and supervision, experience has shown that they are prone to overemphasi*ing small,

atypical bank erosion Dhot spots, even when asked to score more representative banks.

=.0 Re2ere,"e/

-arrelson 3. 3., /awlins, 3. J. and 2otyondy L. 2. &''


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(:&;) 9;9G rathbunjPmichigan.gov



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-!#i2ie# B+,7 Er!/i!, H++r# I,#e (BEHI) ie'# !r%

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(Av*. 9)

ank ?ngle

(degrees)

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A&&e,#i . E+%&'e/ !2 Di22ere, B+,7 C!,#ii!,/ i, S!$5er, -i"5i*+, Sre+%/

i*$re A. Tri4$+r6: K+'+%+!! River w+er/5e#

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BEHI S"!re M .= (;er6 '!w)

i*$re B. K+'+%+!! River

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&re6 *!!# /5+&e.



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i*$re C. R!$*e River

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R!! De&58B+,7 Hei*5 J 0.>1.0

R!! De,/i6 J =1

bank erosion hazard index (behi)

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