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High-water marks are like footprints left behind by a flood — they show how high the water reached during a flood event. High-water marks serve as valuable data points for both educational purposes and scientific research, helping us understand past and recent flood events. Collecting this information is an essential and time-sensitive task for understanding flood risk and improving public safety.
Flooding along streams, rivers, lakes, and oceans is a natural process. But humans live and work near these bodies of water, and flooding can have significant effects on our communities, including the loss of life and property.
The U.S. Geological Survey (USGS) operates a national network of thousands of streamgages to monitor water levels and streamflow. This real-time data is crucial during floods, providing local communities with timely information about changing stream conditions and fueling flood forecasts by the National Weather Service.
But floods affect areas much broader than where USGS streamgages are located. After floodwaters recede, USGS hydrologists will visit impacted areas to find visual evidence of peak flood-water heights or edges, known as "high-water marks." It's important to find and record high-water marks before nature or human activity destroys the evidence, so teams must act quickly to identify any high-water marks before they disappear. Documenting the maximum height of floodwaters is essential so communities know where to target recovery efforts and plan for future floods.
The U.S. Geological Survey (USGS) often partners with the Federal Emergency Management Agency (FEMA), U.S. Army Corps of Engineers, and other organizations to map high-water marks in flooded areas, providing crucial data on the extent and severity of flooding. Once enough high-water marks have been collected and surveyed, scientists can determine the extent and depth of floodwaters for future planning and mitigation efforts.
Floods can leave behind many types of high-water marks like deposited mud, piles of snagged debris, and erosion scars. Proper identification of high-water marks – and their accuracy - requires experience and an understanding of how floodwaters create them and how surrounding environments influence their appearance. While high-water marks serve as a valuable tool, it is important to recognize that there is a level of uncertainty (usually provided in tenths of a foot) associated with the identification of high-water marks.
High-water marks left behind by relatively calm, low-energy flood waters, creating smooth and even depositions with smaller uncertainty.
Turbid water can leave a "mud line" (or sometimes "foam line" or "stain line") on nonporous surfaces like buildings or paved roads when it recedes after flooding. These lines can be reliable indicators of high-water marks, particularly those found on hard surfaces within structures—especially when deposited by tranquil water. Mud lines on natural features like grasses or shrubs can also serve as high-water marks and are generally easier to identify from a distance.
Porous materials such as wood and concrete can absorb floodwater, leaving a stain line that could indicate a flood peak. However, because these materials can wick water higher than the actual peak water surface, high-water elevation may be overestimated. To ensure accuracy, hydrographers search for corroborating high-water marks, especially those found on nearby nonporous surfaces.
Seed lines, formed when fine materials float on top of tranquil water and remain on objects after floodwaters recede, can be left on tree trunks, bridge piers, buildings, and other objects in the flooded reach of a stream. Seed lines can be more reliable than mud lines because they are not prone to wicking, but they can be easily disturbed by wind or touch.
Debris lines are trails of twigs, grasses, and other small debris left on sloping ground at the edge of a river where calmer water, as it receded, deposited the material. Debris lines can be less reliable than seed lines due to their coarser structure and tendency to sag.
When floods recede during freezing periods, ice sheets may form at the water surface. As the under-surface water recedes, suspended plates of ice, referred to as ice rings, may be left behind around cold objects such as fence posts or vegetation.
Higher-velocity stream reaches are associated with increased sediment transport and high-water marks that signify high-energy flows. It can be more difficult to assess their reliability due to factors like wave action and run-up on obstructions.
When the flow of water erodes a stream bank, a rapid-high-water mark called a cut line or scour line can form.
Wash lines indicate the removal of loose material from the top of the ground surface without carving away significant amounts of soil, revealing a "cleaner" look than the adjacent non-flooded soil. Wash lines can also be identified where leaf litter has been removed or grasses have been folded down in the direction of flow.
Debris snags (sometimes called “trash snags” or “flood trash” in urban settings) are formed when coarse debris collects on an obstruction in the water, such as a structure, pole, fence, guy wire, tree, boulder, or bush.
The USGS relies on high-water marks to verify peak stage at most streamgages. While many of these marks are natural flood deposits, the USGS also uses practical, man-made recorders. These devices consistently and conveniently capture high-water events, preserving the marks for scheduled site visits.
Crest-stage gages (CSG) are the most common engineered high-water mark recorders in the USGS. A CSG contains a long wooden, aluminum, or plastic stick confined in a vertically mounted steel pipe that functions as a mini stilling well. An index point on each CSG is surveyed to a known elevation shortly after installation and periodically re-surveyed to document any shifting over time. During a flood event, water rises inside the pipe, and a floating layer of granulated cork rises with the water surface and clings to the peak level on the stick. The cork line remains on the stick, protected by the surrounding pipe, until a larger flood floats the cork line higher or until a hydrographer retrieves the stick and records the cork-line height.
Some continuous streamgages consist of stilling wells equipped with floats attached to long, graduated steel tapes that have their own high-water marking indicators. As the tape moves up and down with the float, an electronic recorder at the top of the well records the float level. When water rises inside the well during a flood, a high-water indicator clip attached to the steel tape rises with the float. As the clip encounters the underside of the gage platform, the clip is forced to slide down the tape. The float and tape return to a lower position as the floodwaters recede, and the clip remains in the same location on the tape, recording the peak offset.
Modern technology, including improvements in data storage and transmission, makes it feasible to use image-capture devices to record high-water marks. Still images taken at regular intervals, like those at some USGS HIVIS web cameras, and event-triggered video devices document the height and extent of floodwaters.
Understand floods:
Estimate and map risk:
Raise awareness:
High-water mark information for many flood events can be accessed through the USGS Flood Event Viewer.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.
High-water marks are like footprints left behind by a flood — they show how high the water reached during a flood event. High-water marks serve as valuable data points for both educational purposes and scientific research, helping us understand past and recent flood events. Collecting this information is an essential and time-sensitive task for understanding flood risk and improving public safety.
Flooding along streams, rivers, lakes, and oceans is a natural process. But humans live and work near these bodies of water, and flooding can have significant effects on our communities, including the loss of life and property.
The U.S. Geological Survey (USGS) operates a national network of thousands of streamgages to monitor water levels and streamflow. This real-time data is crucial during floods, providing local communities with timely information about changing stream conditions and fueling flood forecasts by the National Weather Service.
But floods affect areas much broader than where USGS streamgages are located. After floodwaters recede, USGS hydrologists will visit impacted areas to find visual evidence of peak flood-water heights or edges, known as "high-water marks." It's important to find and record high-water marks before nature or human activity destroys the evidence, so teams must act quickly to identify any high-water marks before they disappear. Documenting the maximum height of floodwaters is essential so communities know where to target recovery efforts and plan for future floods.
The U.S. Geological Survey (USGS) often partners with the Federal Emergency Management Agency (FEMA), U.S. Army Corps of Engineers, and other organizations to map high-water marks in flooded areas, providing crucial data on the extent and severity of flooding. Once enough high-water marks have been collected and surveyed, scientists can determine the extent and depth of floodwaters for future planning and mitigation efforts.
Floods can leave behind many types of high-water marks like deposited mud, piles of snagged debris, and erosion scars. Proper identification of high-water marks – and their accuracy - requires experience and an understanding of how floodwaters create them and how surrounding environments influence their appearance. While high-water marks serve as a valuable tool, it is important to recognize that there is a level of uncertainty (usually provided in tenths of a foot) associated with the identification of high-water marks.
High-water marks left behind by relatively calm, low-energy flood waters, creating smooth and even depositions with smaller uncertainty.
Turbid water can leave a "mud line" (or sometimes "foam line" or "stain line") on nonporous surfaces like buildings or paved roads when it recedes after flooding. These lines can be reliable indicators of high-water marks, particularly those found on hard surfaces within structures—especially when deposited by tranquil water. Mud lines on natural features like grasses or shrubs can also serve as high-water marks and are generally easier to identify from a distance.
Porous materials such as wood and concrete can absorb floodwater, leaving a stain line that could indicate a flood peak. However, because these materials can wick water higher than the actual peak water surface, high-water elevation may be overestimated. To ensure accuracy, hydrographers search for corroborating high-water marks, especially those found on nearby nonporous surfaces.
Seed lines, formed when fine materials float on top of tranquil water and remain on objects after floodwaters recede, can be left on tree trunks, bridge piers, buildings, and other objects in the flooded reach of a stream. Seed lines can be more reliable than mud lines because they are not prone to wicking, but they can be easily disturbed by wind or touch.
Debris lines are trails of twigs, grasses, and other small debris left on sloping ground at the edge of a river where calmer water, as it receded, deposited the material. Debris lines can be less reliable than seed lines due to their coarser structure and tendency to sag.
When floods recede during freezing periods, ice sheets may form at the water surface. As the under-surface water recedes, suspended plates of ice, referred to as ice rings, may be left behind around cold objects such as fence posts or vegetation.
Higher-velocity stream reaches are associated with increased sediment transport and high-water marks that signify high-energy flows. It can be more difficult to assess their reliability due to factors like wave action and run-up on obstructions.
When the flow of water erodes a stream bank, a rapid-high-water mark called a cut line or scour line can form.
Wash lines indicate the removal of loose material from the top of the ground surface without carving away significant amounts of soil, revealing a "cleaner" look than the adjacent non-flooded soil. Wash lines can also be identified where leaf litter has been removed or grasses have been folded down in the direction of flow.
Debris snags (sometimes called “trash snags” or “flood trash” in urban settings) are formed when coarse debris collects on an obstruction in the water, such as a structure, pole, fence, guy wire, tree, boulder, or bush.
The USGS relies on high-water marks to verify peak stage at most streamgages. While many of these marks are natural flood deposits, the USGS also uses practical, man-made recorders. These devices consistently and conveniently capture high-water events, preserving the marks for scheduled site visits.
Crest-stage gages (CSG) are the most common engineered high-water mark recorders in the USGS. A CSG contains a long wooden, aluminum, or plastic stick confined in a vertically mounted steel pipe that functions as a mini stilling well. An index point on each CSG is surveyed to a known elevation shortly after installation and periodically re-surveyed to document any shifting over time. During a flood event, water rises inside the pipe, and a floating layer of granulated cork rises with the water surface and clings to the peak level on the stick. The cork line remains on the stick, protected by the surrounding pipe, until a larger flood floats the cork line higher or until a hydrographer retrieves the stick and records the cork-line height.
Some continuous streamgages consist of stilling wells equipped with floats attached to long, graduated steel tapes that have their own high-water marking indicators. As the tape moves up and down with the float, an electronic recorder at the top of the well records the float level. When water rises inside the well during a flood, a high-water indicator clip attached to the steel tape rises with the float. As the clip encounters the underside of the gage platform, the clip is forced to slide down the tape. The float and tape return to a lower position as the floodwaters recede, and the clip remains in the same location on the tape, recording the peak offset.
Modern technology, including improvements in data storage and transmission, makes it feasible to use image-capture devices to record high-water marks. Still images taken at regular intervals, like those at some USGS HIVIS web cameras, and event-triggered video devices document the height and extent of floodwaters.
Understand floods:
Estimate and map risk:
Raise awareness:
High-water mark information for many flood events can be accessed through the USGS Flood Event Viewer.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.
High-water marks provide valuable data for understanding recent and historical flood events. The proper collection and recording of high-water mark data from perishable and preserved evidence informs flood assessments, research, and water resource management.