U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3136

June 2006

A CSG is a 2-inch-diameter steel casing with intake holes in 

the bottom cap and a vent hole in the top cap. A wooden lath 

is placed inside the casing and shredded cork is placed in the 

bottom cap. As the water rises and enters the casing, the cork 

floats on the surface. As the water recedes, bits of cork adhere 

to the lath, forming a line at the water’s highest level. The peak 

stage is then measured from the lath by field personnel during 

the next site visit.

An ACSG is a self-contained data-logging pressure transducer. 

The transducer is installed in a CSG pipe (fig. 2). During a 

flood, the transducer measures the hydrostatic pressure of the 

water column from which the peak stage is measured. The 

data logger records the stage and time of occurrence during the 

streamflow event as long as the ACSG is installed low enough 

to record the lower flows. 

Two types of pressure transducers have been used: a 

differential-pressure transducer and an absolute-pressure 

transducer.

Differential-pressure transducers correct for barometric 

pressure and require vent tubes. The vent opening cannot be submerged; thus, the vent tube must be installed 

higher than the estimated maximum possible flood. An 

example of a differential-pressure transducer with the 

attached cable is shown in figure 3.

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Introduction

The measurement of highly transient streamflow in ephemeral streams in the desert southwest (fig. 1) presents many 

challenges. Most streamflow data for ephemeral streams are 

collected using a traditional crest-stage gage (CSG). However, 

CSGs are limited in the data that can be collected because only 

the peak stage of the highest streamflow event that occurred 

since the previous site visit is measured. This results in incomplete documentation of streamflow at the site.

Streamflow data in ephemeral channels are used for floodfrequency analysis (Waltemeyer, 1996). Flood-frequency 

estimates are necessary for design of hydraulic structures such 

as bridges, culverts, dams, levees, and channels; thus, the 

more data collected, the better the analysis. In 2002, the 

U.S. Geological Survey (USGS), in cooperation with the New 

Mexico Department of Transportation, began installing submersible pressure transducers at CSG sites to better measure 

and record streamflow in ephemeral streams. Since 2002, 35 of 

the 80 CSGs in New Mexico have been converted to automated 

crest-stage gages (ACSGs).

This fact sheet describes the advantages of using an ACSG. 

Included is a brief discussion of the differential-(vented) and 

absolute-pressure transducers that are used for the ACSGs. 

Selected peak-stage data collected using a CSG cork-line 

measurement and peak-flow data collected using an ACSG are 

compared for 12 sites.

Figure 1.  Near peak flow in an ephemeral stream near Variadero,

N. Mex. (Garita Creek at Highway 104 Bridge), September 9, 2002.

In cooperation with the New Mexico Department of Transportation

Automated Crest-Stage Gage Application 

in Ephemeral Streams in New Mexico

Traditional Crest-Stage Gage and 

Automated Crest-Stage Gage

Figure 2.  The 2-inch-diameter steel casing of a traditional creststage gage in which a transducer is installed. The gage is attached

to a wooden lath and secured with nylon ties.
The pressure transducer measures and records stage for a 

user-selected time interval and is event-activated at 0.15 foot 

after submergence of the transducer begins. The transducer 

measures and records the stage as long as the water level 

continues to increase or decrease 0.15 foot. During periods 

of no flow, the transducer measures and records at 8.25-hour 

intervals. 

A hydrograph of data collected by a pressure transducer during 

a streamflow event in an ephemeral channel is shown in figure 

4. The data recorded by the transducer include date, time, and 

continuous stage data during each event.

At each site where an ACSG is installed, the CSG is retained 

so that the peak stage measured by the pressure transducer 

can be verified with the peak stage indicated by the cork-line 

measurement of the CSG. The accuracy of a cork line is 0.01 

foot. The CSG is retained as a backup measurement of peak 

stage if the transducer fails (since 2002, no transducers have 

failed).

A pressure transducer has the capacity to store 1 megabyte 

of data; thus, a site can be visited once per year if desired. A 

potential problem of one site visit per year, however, is that 

the data record can be lost if the transducer experiences 

internal problems, is damaged during a streamflow event, 

or is vandalized.

Absolute-pressure transducers are completely enclosed 

and also respond to changes in barometric pressure. 

An absolute-pressure transducer acts as a barometer 

prior to and during streamflow events; therefore, if the 

barometric pressure at the site is known, the pressure 

can be factored out of the measurement. Because an 

absolute-pressure transducer is enclosed, submergence is 

not a concern. This transducer measures water depth to 

as much as 69 feet. Only absolute-pressure transducers 

are now used in New Mexico.

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Figure 3.  Example of a differential-pressure

transducer. Note the cable extended above

the transducer on the wooden lath.

Figure 4. Hydrograph showing peak flow and a smaller peak during one streamflow event at the crest-stage gage site

Yeso Creek near Fort Sumner, N. Mex., July 3, 2002.
An ACSG allows easy installation of the data-logging 

pressure transducer (fig. 5);

An ACSG records date, time, and continuous-stage data 

during each streamflow event;

An ACSG allows the user to determine the number of 

streamflow events between site visits, not just one peak 

flow as with a CSG;

An ACSG does not require field calibration;

An ACSG requires fewer site visits than a CSG;

An ACSG allows the user to select the recording 

time interval;

An ACSG is streamflow-event activated;

An ACSG is more expensive than a CSG; and

An ACSG with a differential (vented) transducer must 

be installed higher than the estimated maximum possible 

flood because the cable attached to the transducer cannot 

be submerged more than 30 minutes without failure and 

damage to the transducer.

Data collected at 11 sites using CSG cork-line peak-stage 

measurements and ACSG peak-stage measurements are compared in table 1. The difference in peak stage measured by the 

CSG and peak stage measured by the ACSG for 16 separate 

storms ranged from +0.07 to -0.42 foot.

All data listed in table 1 were recorded at 5-minute intervals by 

the ACSGs. Most discrepancies listed are within acceptable limits given the type of streamflow measured in ephemeral streams. 

Some of the larger discrepancies (for example, Burro Canyon 

near Lindrith; -0.42 foot) indicate that the 5-minute recording 

interval was too great. The factor exerting the greatest influence is storm intensity, but additional factors include basin size, 

shape, and area. Thus, a recording interval less than 5 minutes 

may be required to record the peak stage.

Waltemeyer, S.D., 1996, Analysis of the magnitude and frequency of peak discharge and maximum observed 

peak discharge in New Mexico: U.S. Geological Survey 

Water-Resources Investigations Report 96–4112, 79 p. 

Moore, S.J., Stewart, A.E., Constantz, J., and Sarma, L., 

2000, Instrumentation of two ephemeral streams in central 

New Mexico to improve understanding of streamflows and 

ground-water exchanges [abs.]: EOS, Transactions, American 

Geophysical Union, v. 81, no. 48, p. 485.

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A CSG is inexpensive;

A CSG has a sturdy, rugged design that can withstand 

flash floods and destructive streamflow;

A CSG can measure peak stage to within 

0.01-foot accuracy;

A CSG only measures peak stage of the highest 

streamflow event;

A CSG does not record date, time, or continuous 

stage data;

A CSG does not record all streamflow events between 

site visits; and

A CSG may not measure a subsequently higher peak 

stage if sediment (sand, silt, and clay) is deposited on 

the shredded cork in the bottom cap of the gage during

a streamflow event.

An ACSG uses the same external housing as a 

traditional CSG;

An ACSG can be used as an outside reference for 

verification at a regular streamflow-gaging station;

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Automated Crest-Stage Gage

Traditional Crest-Stage Gage

Figure 5. USGS hydrologist attaching an absolute-pressure

transducer to a bridge piling at Arroyo Hondo near Santa Fe,

N. Mex.

Selected References

Traditional Crest-Stage Gage in 

Comparison to Automated 

Crest-Stage Gage

Comparison of Data 
U.S. Geological

Survey station

name

U.S. Geological

Survey station

number

Traditional

crest-stage

gage observed

stage, in feet

Automated

crest-stage

gage recorded

stage, in feet

Stage

difference,

in feet

Accuracy,

stage

difference as

percentage of

transducer

range (30 psi),

0–69 feet

Type of

transducer

Raton Creek at

Raton

07201000 1.08 0.83 -0.25 -0.36 Absolute

Sand Draw near

Clayton 

07227300 4.57 4.48 -0.09 -0.13 Absolute

Running Water

Draw near

Clovis

08080600 2.72 2.76 +0.04 0.06 Absolute

San Cristobal

Arroyo near

Galisteo

08317600 1.72

1.94

1.03

1.12

1.73

1.94

0.91

1.03

+0.01

+0.00

 -0.12

 -0.09

 0.01

 0.00

-0.17

-0.13

Absolute

San Pedro

Creek near

Golden

08318900 1.28 1.01 -0.27 -0.39 Absolute

Tecolote Creek

at Tecolote

08379600 1.92 1.71 -0.21 -0.30 Absolute

Yeso Creek

near Fort 

Sumner

08385600 5.14

4.40

3.57

5.10

4.47

3.52

-0.04

+0.07

-0.02

-0.06

0.10

-0.03

Differential

(vented)

Absolute

Big Draw near

Mountainair

08489000 2.35 2.33 -0.02 -0.03 Absolute

Gobernador

Canyon near

Gobernador

09355799 1.24 0.95 -0.29 -0.42 Absolute

Burro Canyon

near Lindrith

09356520 1.92 1.50 -0.42 -0.61 Absolute

Galestena Canyon

tributary

near Black

Rock

09387050 0.59 0.64 +0.05 0.07 Absolute

Table 1. Comparison of traditional and automated crest-stage gage data in New Mexico.

[psi, pounds per square inch]

For more information:

Scott D. Waltemeyer

sdw@usgs.gov

505-830-7953