ENG 6250 Rapid Ordinary High Water Mark (OHWM) Field Identificati

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U.S. Army Corps of Engineers (USACE)
RAPID ORDINARY HIGH WATER MARK (OHWM) FIELD IDENTIFICATION DATA SHEET

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From Approved OMB No. 0710-OHWM
Expires: xx-xx-xxxx

The proponent agency is Headquarters USACE CECW-CO-R.

AGENCY DISCLOSURE NOTICE
The public reporting burden for this collection of information, 0710-OHWM, is estimated to average 30 minutes per response, including the time for
reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of
information. Send comments regarding the burden estimate or burden reduction suggestions to the Department of Defense, Washington Headquarters
Services, at whs.mc-alex.esd.mbx.dd-dod-information-collections@mail.mil. Respondents should be aware that notwithstanding any other provision of
law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control
number.
Project ID #:

Site Name:

Date and Time:

Location (lat/long):

Investigator(s):

Step 1 Site overview from remote and online resources
Check boxes for online resources used to evaluate site:
gage data

LiDAR

geologic maps

climatic data

satellite imagery

land use maps

aerial photos

topographic maps

Other:

Describe land use and flow conditions from online resources.
Were there any recent extreme events (floods or drought)?

Step 2 Site conditions during field assessment. First look for changes in channel shape, depositional and erosional features, and changes in
vegetation and sediment type, size, density, and distribution. Make note of natural or man-made disturbances that would affect flow and
channel form, such as bridges, riprap, landslides, rockfalls etc.

Step 3 Check the boxes next to the indicators used to identify the location of the OHWM.
OHWM is at a transition point, therefore some indicators that are used to determine location may be just below and above the OHWM. From
the drop-down menu next to each indicator, select the appropriate location of the indicator by selecting either just below `b', at `x', or
just above `a' the OHWM.
OHWM. Go to page 2 to describe overall rationale for location of OHWM, write any additional observations, and to attach a photo log.
Geomorphic indicators
Channel bar:

Break in slope:
on the bank:

shelving (berms) on bar:

undercut bank:

unvegetated:

valley bottom:
Other:
Shelving:
shelf at top of bank:
natural levee:
man-made berms or levees:
other
berms:

vegetation transition
(go to veg. indicators)
sediment transition
(go to sed. indicators)
upper limit of deposition
on bar:
lnstream bedforms and other
bedload transport evidence:
deposition bedload indicators
(e.g., imbricated clasts,
gravel sheets, etc.)
bedforms (e.g., poofs,
riffles, steps, etc.):

erosional bedload indicators
(e.g., obstacle marks, scour,
smoothing, etc.)
Secondary channels:
Sediment indicators
Soil development:
Changes in character of soil:
Mudcracks:
Changes in particle-sized
distribution:

to

transition from

upper limit of sand-sized particles
silt deposits:

Vegetation Indicators
Change in vegetation type
and/or density:
Check the appropriate boxes and select
the general vegetation change (e.g.,
graminoids to woody shrubs). Describe
the vegetation transition looking from
the middle of the channel, up the
banks, and into the floodplain.
vegetation
absent to:
moss to:
Other observed indicators?

forbs to:
graminoids to:
woody
shrubs to:
deciduous
trees to:
coniferous
trees to:
Vegetation matted down
and/or bent:

Exposed roots below
intact soil layer:
Ancillary indicators
Wracking/presence of
organic litter:
Presence of large wood:
Leaf litter disturbed or
washed away:
Water staining:
Weathered clasts or bedrock:

Describe:

ENG FORM 6250, SEP 2021

PREVIOUS EDITIONS ARE OBSOLETE.

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Project ID #:
Step 4 Is additional information needed to support this determination?

Yes

No

If yes, describe and attach information to datasheet:

Step 5 Describe rationale for location of OHWM

Additional observations or notes

Attach a photo log of the site. Use the table below, or attach separately.
Photo log attached?

Yes

No

If no, explain why not:

List photographs and include descriptions in the table below.
Number photographs in the order that they are taken. Attach photographs and include annotations of features.
Photo
Number

Photograph description

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OHWM Field Identification Datasheet Instructions and Field Procedure
Step 1

Site overview from remote and online resources
Complete Step 1 prior to site visit.
Online Resources: Identify what information is available for the site. Check boxes on datasheet next to the resources used to
assess this site.
a. gage data
e. topographic maps
b. aerial photos
f. geologic maps
c. satellite imagery
g. land use maps
d. LiDAR
h. climatic data (precipitation and temperature)
Landscape context: Use the online resources to put the site in the context of the surrounding landscape.
a. Note on the datasheet under Step 1:
i. Overall land use and change if known
ii. Recent extreme events if known (e.g., flood, drought, landslides, debris flows, wildfires)
b. Consider the following to inform weighting of evidence observed during field visit.
i. What physical characteristics are likely to be observed in specific environments?
ii. Was there a recent flood or drought? Are you expecting to see recently formed or obscured indicators?
iii. How will land use affect specific stream characteristics? How natural is the hydrologic regime? How stable has the landscape been
over the last year, decade, century?

Step 2

Site conditions during the field assessment (assemble evidence)
a. Identify the assessment area.
b. Walk up and down the assessment area noting all
the potential OHWM indicators.
c. Note broad trends in channel shape, vegetation,
and sediment characteristics.
i. Is this a single thread or multi-thread system?
Is this a stream-wetland complex?
ii. Are there any secondary and/or floodplain channels?
iii. Are there obvious man-made alterations to the system?
iv. Are there man-made (e.g., bridges, dams, culverts) or
natural structures (e.g., bedrock outcrops, Large Wood
jams) that will influence or control flow?

d. Look for signs of recurring fluvial action.
i. Where does the flow converge on the landscape?
ii. Are there signs of fluvial action (sediment sorting,
bedforms, etc.) at the convergence zone?
e. Look for indicators on both banks. If the opposite bank is not
accessible, then look across the channel at the bank.
f. In Step 2 of the datasheet describe any adjacent land use or
flow conditions that may influence interpretation of each line of
evidence.
i. What land use and flow conditions may be affecting your ability
to observe indicators at the site?
ii. What recent extreme events may have caused changes to the
site and affected your ability to observe indicators?

Step 3a List evidence
Assemble evidence by checking the boxes next to each line of evidence:
a. If needed, use a separate scratch datasheet Context is important when assembling evidence. For instance, pool development may be
to check boxes next to possible indicators,
an indicator of interest on the bed of a dry stream, but may not be a useful indicator to take
or check boxes of possible indicators in
note of in a flowing stream. On the other hand, if the pool is found in a secondary channel
pencil and use pen for final decision.
adjacent to the main channel, it could provide a line of evidence for a minimum elevation of
b. If using fillable form, then follow the
high flows. Therefore, consider the site context when deciding which indicators provide
instructions for filling in the fillable form.
evidence for identifying the OHWM. Explain reasoning in Step 5.
Questions to consider while making observations and listing evidence at a site:
Geomorphic indicators
Where are the breaks in slope?
Are there identifiable banks?
Is there an easily identifiable
top of bank?
Are the banks actively eroding?
Are the banks undercut?
Are the banks armored?
Is the channel confined by
the surrounding hillslopes?
Are there natural or man-made
berms and levees?
Are there fluvial terraces?
Are there channel bars?

Sediment and soil indicators
Where does evidence of
soil formation appear?

Ancillary indicators
Is there organic litter
present?

Is there vegetation growing on the channel bed?
Are there mudcracks present?
Is there evidence of sediment
sorting by grain size?

Are the following features of fluvial transport present?
Evidence of erosion: obstacle marks, scour, armoring
Bedforms; riffles, pools, steps, knickpoints/headcuts
Evidence of deposition: imbricated clasts, gravel sheets, etc.
ENG FORM 6250, SEP 2021

Vegetation Indicators
Where are the significant transitions in
vegetation species, density, and age?

Is there any leaf litter
If no, how long does it take for the non-tolerant
disturbed or washed
vegetation to establish relative to how often flows away?
occur in the channel?
Where are the significant transitions in
vegetation?

Is there large wood
deposition?

Is the vegetation tolerant of flowing water?

Is there evidence of
water staining?

Has any vegetation been flattened by flowing
water?

In some cases, it may be helpful to explain why an indicator was NOT at
the OHWM elevation, but found above or below. It can also be useful to
note if specific indicators (e.g., vegetation) are NOT present. For instance,
note if the site has no clear vegetation zonation.
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OHWM Field Identification Datasheet Instructions and Field Procedure
Step 3b Weight each line of evidence and weigh body of evidence
Weight each indicator by considering its importance based upon:
a. Relevance:
i. Is this indicator left by low, high, or extreme flows?

*Landscape context from Step 1 can help
determine the relevance, strength, and reliability
of the indicators observed in the field.

Tips on how to assess the indicator relative to type of flow:
Consider the elevation of the indicator relative to the channel bed.
*Information in Chapter 2 of the OHWM field manual
provides information on specific indicators which can
assist in putting these in context and determining
If the stream is currently at baseflow and indicator is adjacent to that, relevance, strength, and reliability.
then it is likely a low flow indicator. The difference between high and
What is the current flow level based on season or nearby gages?

Consider the elevation of the indicator relative to the current flow.

extreme flow indicators can sometimes be difficult to determine.
ii. Did recent extreme events and/or land use affect this indicator?
1. Recent floods may have left many extreme flow indicators, or temporarily altered channel form.
Other resources will likely be needed to support any OHWM identification at this site. Field evidence of
the OHWM may have to wait for the site to recover from the recent flood.
2. Droughts may cause field evidence of OHWM to be obscured, because there has been an extended time since the last high flow
event. There can be overgrowth of vegetation or deposition of material from surrounding landscape that can obscure indicators.
3. Both man-made (e.g., dams, construction, mining activities, urbanization, agriculture, grazing) and natural (e.g., fires, floods, debris
flows, beaver dams) disturbances can all alter how indicators are expected to appear at a site. Chapter 6 and Chapter 7 of the
OHWM field manual provides specific case-studies that can help in interpreting evidence at these sites.
b. Strength:
i. Is this indicator persistent across the landscape?
1. Look up and downstream and across the channel to see if you see the same indicator at multiple locations.
2. Does the indicator occur at the same elevation as other indicators?
c. Reliability:
i. Is this indicator persistent on the landscape over time? Will this indicator still persist across seasons?
1. This can be difficult to determine for some indicators and may be specific to climatic region (in terms of persistence of vegetation)
and history of land use or other natural disturbances.
2. Chapter 2, Chapter 6, and Chapter 7 of the OHWM field manual describes each indicator in detail and provides examples of areas
where indicators are difficult to interpret.
d. Weigh body of evidence:
i. Combine weights: integrate the weighted line of evidence (relevance, strength, reliability) of each indicator.
ii. For each of the observed indicators, which are more heavily weighted? Where do high value indicators co-occur along the stream
reach? Do they co-occur at a similar elevation along the banks relative to water surface (or channel bed if there is no water).
iii. On datasheet, select the indicators used to identify the OHWM. Information in Chapter 2 of the OHWM field manual provides
descriptions of specific indicators which can assist in putting these in context and determining relevance, strength, and relieability.
e. Take photographs of indicators and attach a log using either page 2 of datasheet or another method of logging photos.
i. Annotate photos with descriptions of indicators.
Step 4

Is additional information needed? Are other resources needed to support the lines of evidence observed in the field?
a. If additional resources are needed, then repeat steps 3a and 3b for the resources selected in Step 1 of assembling, weighting, and
weighing evidence collected from online resources. Chapter 5 of the OHWM field manual provides information on using online resources.
b. Any data collected from online tools have strengths and weaknesses. Make sure these are clear when determining relevance, strength,
and reliability of the remotely collected data. Clearly describe why other resources were needed to support the lines of evidence observed
in the field, as well as the relevance, strength, and reliability of the supporting data and/or resources.
c. Attach any remote data and data analysis to the datasheet.

Step 5

Describe rationale for location of OHWM:
a. Why do the combination of indicators represent the OHWM?
b. If there are multiple possibilites for the OHWM, explain why there are two (or more) possibilities. Include any relevant discussion on why
specific indicators were not included in the final decision.
c. If needed, add additional site notes on page 2 of the datasheet under Step 5.

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