Form ENG Form 6250 ENG Form 6250 Interim Draft Rapid Ordinary High Water Mark (OHWM) Fiel

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

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Form Approved OMB No. 0710-0024
Expires: 2024-04-30

The proponent agency is Headquarters USACE CECW-COR.

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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 Mark the boxes next to the indicators used to help identify the location of the OHWM.
OHWM is at a transition point, therefore some indicators used to identify the location of the OHWM may be just below or above the OHWM.
Make a slash in boxes next to indicators that are helpful in identifying the OHWM. After the initial assessment, those indicators
identified at the OHWM elevation should be changed from slashes to x's. Note, it is not necessary to mark indicators that are present
but do not help inform identification of the OHWM.
Go to page 2 to describe overall rationale for location of OHWM, write any additional observations, and attach a photo log.
Geomorphic indicators
Break in slope

Channel bar

on the bank

shelving (berms) on bar

undercut bank

unvegetated
vegetation transition (go to veg.
indicators)
sediment transition (go to sed.
indicators)

valley bottom
Other:
Shelving

upper limit of deposition on bar

shelf at top of bank
natural levee
man-made berms or levees
other berms:

lnstream bedforms and other
bedload transport evidence
deposition bedload indicators
(e.g., imbricated clasts,
gravel sheets, etc.)
bedforms (e.g., pools,
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

Weathered clasts or bedrock
Vegetation indicators (Consider the vegetation transition looking from the middle of the channel,
up the banks, and into the floodplain)
Change in vegetation type from

to

Change in density of vegetation.

Other physical indicators
Sediment deposited on vegetation or
structures
Wracking/presence of organic litter

Other vegetation observations
Presence of large wood
Leaf litter disturbed or washed away
Exposed roots below intact soil layer
Other observed indicators?

Vegetation matted down and/or bent:

Water staining

Describe:

ENG FORM 6250, FEB 2024

PREVIOUS EDITIONS ARE OBSOLETE.

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Project ID #:
Step 4 Was additional information used to support identification of the OHWM?

Yes

No

If yes, describe and attach information to data sheet:

Step 5 Is an OHWM present at this site?

Yes

No

Describe rationale for location of OHWM or lack thereof by describing any observed indicators (at, above, and/or below the OHWM location).

Additional observations or notes

Attach an imagery log of the site.
Imagery log attached?

Yes

No

If no, explain why not:

List photographs, or other imagery/sketches, and include descriptions in the table below.
Number photographs in the order that they are taken. Attach imagery and include annotations of features.
Imagery
Number

ENG FORM 6250, FEB 2024

Imagery description

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OHWM Field Identification Datasheet Instructions and Field Procedure
Step 1
visit.

Site overview from remote and online resources (Chapter 5)

Complete Step 1 prior to site

Online Resources: Identify what information is available for the site. Check boxes on data sheet 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. (Chapter 4)
a. Note on the data sheet 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)
iii. Erosional and depositional environments
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) (Chapter 1 and 3)
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 data sheet 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 (Chapter 2 and 3)
Assemble evidence by marking each box with a slash next to each line of evidence.
If using fillable form, then follow the instructions Context is important when assembling evidence. For instance, pool development may be
for filling in the fillable form.
an indicator of interest on the bed of a dry stream, but may not be a useful indicator to take
note of in a flowing stream. On the other hand, if the pool is found in a secondary channel
adjacent to the main channel, it could provide a line of evidence for a minimum elevation of
high flows. Therefore, consider the site context when deciding which indicators provide
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?

Is there vegetation growing on the channel bed?

Other physical
indicators
Is there organic litter
present?

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, FEB 2024

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

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

Is there large wood
deposition?
Is there evidence of
water staining?

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 (Chapter 1 and 3)
*Landscape context from Step 1 (Chapter 4) can help
Consider importance of each indicator by assessing the following:
determine the relevance, strength, and reliability
a. Relevance:
of the indicators observed in the field.
i. Is this indicator left by low, high, or extreme flows? Did recent
extreme events and/or land use affect this indicator?
*Information in Chapter 2 of the OHWM field manual
iI. Consider the elevation of the indicator relative to the channel bed.
provides information on specific indicators that can
assist in putting these in context and determining
What is the current flow level based on season or nearby gages?
relevance, strength, and reliability.
iii. Consider the elevation of the indicator relative to the current flow.
If the stream is currently at baseflow and indicator is adjacent to that,
then it is likely a low-flow indicator. The difference between high-and
extreme-flow indicators can sometimes be difficult to determine.
iv. 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.
v. 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.
vi. Both man-made (e.g., dams, construction, mining activities, urbanization, agriculture, grazing) and natural (e.g., fires, floods, debris
flows, beaver dams) disturbances can alter how indicators are expected to appear at a site. Chapter 6 and Chapter 7 of the
OHWM field manual provide 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 describe each indicator in detail and provide examples of areas
where indicators are difficult to interpret.
Step 4

Was additional information used to support identification of the OHWM? Are other resources used 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 and weighting
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 used 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 data sheet.

Step 5

Describe rationale for location of OHWM: (Chapter 1 and Chapter 3)
a. Weigh body of evidence:
Combine information from Step 3b: Why do the combination of indicators represent the OHWM?
i. Integrate the lines of evidence (relevance, strength, and reliability) of each indicator.
ii. Consider which indicators are high value indicators that co-occur along the stream reach. Which indicators are most relevant to
identifying high flow elevations, which are most persistent across the landscape, and which are most persistent over time?
iii. Which indicators that are found above and below the location of the OHWM were helpful in identifying the elevation of the OHWM?
b. If there is more than one possible location explain why, If there is more than one possible location explain why. 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 or attach additional sketches and field observations to the
data sheet.
d. Take photographs of indicators and attach an imagery log using page 2 of datasheet or another method of logging images.
i. Annotate images with descriptions of indicators.

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