Delaware River at Montague Ice Affected Discharge Measurement

Completed

By New Jersey Water Science Center March 26, 2026

On February 11, 2026, a team of scientists from the New Jersey Water Science Center made a discharge measurement at the USGS 01438500 Delaware River at Montague, New Jersey monitoring site during ice cover conditions. This is the first time since February 1999 that this type of measurement was made at this site. Frigid winter weather conditions made the measurement both necessary and possible.

01438500 Delaware River at Montague Water Data

Map of New Jersey with markers showing surface water monitoring site locations

Current conditions for 0138500 Delaware River at Montague, New Jersey Monitoring Site

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01438500 Delaware River at Montague Webcam

Looking out on the tree banked river from a high vantage point.

HIVIS Camera feed from Delaware River at Montague, New Jersey

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How does Ice on Rivers and Streams Affect USGS Streamflow Data

Three side by side images of ice forming overtime on a river surface

During colder winter periods ice can form in rivers and streams altering the natural relationship between stage and discharge (flow).

Learn about Ice

Making a Plan

Measuring the flow under ice is an exploration in logistics. First, the ice needs to be thick enough to safely support the work being done. This does not happen very often in New Jersey, but the arctic surge of January 2026 provided us with optimal conditions in northern New Jersey.

Once it has been determined that ice conditions are likely thick enough for a measurement to be made, a safety plan is put in place because the safety of our scientists is of highest priority. The Local authorities are brought in on the plan for their awareness.

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Starting from the Montague gage house on the right, we fly downstream looking over the frozen river for the best location to work.

Once on site, the location of a cross section for the measurement needs to be determined. An Unmanned Aerial System (UAS) drone is used to survey the local river reach to help identify a potential safe cross section.

Next, boots hit the ground for exploration. The ice cover is tested for stability and to determine uniform conditions. Finally, the measurement cross section is selected. (demarcated on the aerial photograph below).

Aerial view of the Delaware River and the Bridge at Montague, New Jersey with a red line across the river — Aerial view looking downstream at USGS site 01438500 Delaware River at Montague, New Jersey and seeing the bridge over the frozen river with a red highlighted line indicating the intended cross section for the ice measurement.

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Setting up the Measurement

Once the cross section has been selected, USGS scientists navigate onto the ice. A test borehole is drilled, and a wading rod is used to measure the thickness of the ice and verify the safety of the cross section.

After testing the ice thickness, the scientists then proceed to move across the river drilling a series of holes along the way to create a line of typically 15 to 20 holes from near edge to far edge.

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Two scientists standing on a frozen river drilling a hole to check the flow below

Drilling the Delaware Ice

Shoeing the ice flow measuring post's calibrations next to a traditional depth rod

Delaware Ice Measurement Sensor

Scientists taking a reading of the flow under the ice on the river

Delaware Ice Measurement Sampling

Measuring the Flow

Holes are drilled in a straight line across the river roughly along the cross section planned in the previous step. Under ideal conditions, the ice in a cross section should be relatively uniform (the thickness of the ice for this measurement was a consistent 1.2 feet). We also need to account for the thickness of potential slush beneath the ice. Graduation marks on the Acoustic Doppler Current Profiler (ADCP) mount are used to measure the combined ice and slush thickness.

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USGS Scientist Karl Braun pushes the Acoustic Doppler Current Profiler through the ice borehole, pausing due to resistance from the slush layer below. The wind, ice crunching, and a small splash can be heard in the video.

An ADCP, which uses soundwaves to record the movement of particles suspended in the water, is attached to the mount. This unit will be lowered below the ice and slush layers to read the depth and velocity of the flowing waters below.

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Coming Home

Our team of USGS scientists, having completed the long job of collecting the data gather their equipment once more for the trek back to the safety of the shore. There, they will review the collected data to ensure they have collected what they need and pack up for a job well done.

One more UAS Drone pass with a thermal camera is made to look at the site, seeing things in ways we normally don’t see.

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Thermal imagery from a drone looking at the red, warmer water under the ice, and the holes drilled in the frozen Delaware River. As the camera pans to the right, larger red splash zones are seen form the more recent samples, leading to the two USGS scientists working at the most recent site.

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The Final Product

Having collected the data and returned to the warmth of the office, the USGS scientists post process and review the information they collected.

a colored graph showing the flow data collected from the river — Output images from the collected data of the Acoustic Doppler Current Profiler used for the ice measurement at USGS 01438500 Delaware River at Montague, New Jersey.

The top graph shows the velocity direction and magnitude of flow, giving the scientists a quick overview of the flow conditions in each subsection. The lower graph shows the cross-sectional shape of the riverbed with the colored blocks indicating the velocity in each subsection.

An ice affected measurement is not typically used for stage-discharge rating curve development but plotted below shows the amount of backwater created by the ice in the river. The other measurements shown on the graph below are measurements made with clear channel conditions. The ice and slush in the river results in over 1 foot of shift (or backwater) to the normal stage-discharge rating.