USGS Fact Sheet 009-01 March 2001
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Evaluation of Missing Gage-Height Record for Streams and Lakes in Kansas
by Seth E. Studley
Table of Contents
An evaluation of the occurrence and causes of missing gage-height record from stream- and
lake-gaging stations in Kansas from 1987 through 1999 shows that there has been a 40-percent
reduction in the amount of missing gage-height record during the past 13 years. Real-time
gage-height and streamflow data are important to Kansas and the Nation for planning and
decisions related to agriculture, industry, urban water supplies, navigation, riverine and
riparian habitat, and flood-hazard identification. Long-term records from gaging stations are
a cornerstone for national, regional, and local efforts to understand the Nation's water
resources. Any gaps in those long-term records of streamflow and lake levels can mean a gap
in the essential understanding and management of water resources. Reducing the amount of
missing gage-height records, which are used to monitor and manage water resources in Kansas,
is a major concern for the U.S. Geological Survey (USGS).
Collection of flow data for streams and water-level data for lakes is a principal component
of the USGS mission in providing reliable, impartial, and timely information needed to
understand the Nation's water resources. Because gage-height data are used to compute daily
streamflow and lake content, any missing gage-height data affects the quality of the computed
record. As part of ongoing efforts to continually improve the quality and timeliness of
streamflow and lake water-level data, the USGS evaluated the occurrence and causes of missing
gage-height record in Kansas for 1987-99. This summary of the results of that evaluation was
done in collaboration with the USGS Office of Surface Water in Reston, Virginia.
A previous evaluation of the occurrence and causes of missing gage-height record in Kansas
for 1971-81 indicated that the stream- and lake-gaging stations had missing gage-height
record an average of about 15 days per year (about 4 percent of the time) per station during
the 11-year study period (Livingston, 1983). Faulty timers on digital recorders were the
primary cause of missing gage-height record during this period, closely followed by silting
and freezing of the orifice lines and well intakes.
Another evaluation of missing gage-height record (Wahl and Shields, 1989) analyzed data for
USGS offices in Colorado, Iowa, Kansas, Missouri, Montana, Nebraska, New Mexico, North Dakota,
Oklahoma, South Dakota, Texas, Utah, and Wyoming for 1982-86. This evaluation showed a
substantial reduction from 1982 to 1983 in the amount of missing gage-height record caused by
malfunctions of the digital recorder timers resulting from the replacement of the faulty
timers with new solid-state timers beginning in 1982. The total amount of missing gage-height
record, however, remained about the same as that of the 1971-81 evaluation (about 4 percent)
due to increases in other problem categories. Comparison of the occurrence and causes of
missing gage-height record in Kansas from 1987 to 1999 with data from previous evaluations
will help determine whether the occurrence of missing gage-height record in Kansas has changed
with the use of advanced technology equipment such as electronic data recorders and pressure
transducers.
The USGS currently (2001) collects gage-height data at approximately 160 continuous-record
gaging stations in Kansas. Since the mid-1960's, gaging stations generally have been equipped
with bubbler systems for the collection of gage-height record (fig. 1).
In a bubbler system, an orifice is attached securely below the water surface and connected to
a pressure-sensing device by a length of plastic tubing. Pressurized gas (usually nitrogen or
air) is forced through the tubing and out the orifice. Because the pressure in the tubing is a
function of the depth of water above the orifice, a change in the water level of a stream or
lake produces a corresponding change in the pressure in the tubing. Pressure sensors, such as
mechanical manometers or electronic pressure transducers, convert the pressure in the tubing
into height of water above a set datum level referred to as gage height. Graphic recorders,
digital punch-tape recorders, or electronic data loggers record the gage height either
continuously or at preset time intervals, usually 15 minutes. Solar-recharged batteries power
the electrical equipment. Failure of any one of these components can cause missing gage-height
record.
Gaging-station operation changed significantly in 1982 with the introduction of
data-collection platforms (DCP's). The DCP collects gage-height data and transmits it to the
Geostationary Operational Environmental Satellite (GOES) that relays the data to a ground
station and then to USGS offices for dissemination (fig. 2). The data enters the computer system within a few
seconds after satellite transmission. This information then is made available to the public on
the USGS "Current Gage-Height and Streamflow Conditions" Internet site at URL:
http://ks.water.usgs.gov
Station descriptions, updated each year for each gaging station, include installation dates
for new equipment. In 1987, nearly one-half of the gaging stations in Kansas were equipped
with DCP's and by 1997, all of the gaging stations had DCP's (fig. 3). The new technology permits USGS offices to monitor the
operation of the gaging stations continuously and allows them to time visits to gaging
stations to coincide with those times when the need for data is greatest, such as during
floods and to repair or service equipment at the gaging stations.
The introduction of the electronic pressure transducer also has reduced the gaps in
gage-height data. Beginning in 1993, the pressure transducer replaced the mechanical manometer
as the primary gage-height sensor (figs. 3 and
4). Installation and maintenance
of the electronic pressure transducer takes less time than for manometers, and the transducers
are more reliable, resulting in fewer days of missing data.
A few gaging stations currently (2001) are equipped with a new, compact, air
compressor-bubbler system that replaces the compressed-gas cylinder and conoflow (a mechanical
device that regulates the orifice-line pressure and bubble rate). This new device also has the
advantage of a programmable orifice-line purge that can periodically clear the orifice at
gaging stations that have a persistent problem with the blocking of an orifice with silt or
organic growth. The purging of the orifice line at these stations can greatly improve the
accuracy of the gage-height data.
The advances in gaging-station equipment technology have helped to decrease the occurrence of
missing gage-height record by reducing the amount of equipment that can malfunction and by
allowing a quicker response time in repairing or replacing equipment. In addition, hydrologic
technicians have fewer routine tasks to perform during visits to the station, and the
maintenance of the equipment is less time consuming. Technicians no longer need to retrieve
and process digital punch tapes and graphic strip charts. Now, all of the gage-height record
is sent directly to USGS offices by satellite or downloaded onsite to a laptop computer, thus
reducing the opportunity for mechanical malfunctions or human error that can lead to missing
gage-height record.
Station analyses written by the USGS at the end of the water year for each gaging station
include information for determining the occurrence and causes of missing gage-height record
for each year of operation. Any day having less than 12 hours of gage-height data that cannot
be reasonably recovered was considered a day of missing gage-height record. The causes of
missing gage-height record were divided into six problem categories:
Orifice-included problems associated with the orifice line or well-intake systems,
including silted or frozen orifice lines and intakes.
Gage-Height Sensor-included manometer problems and pressure transducer problems
excluding battery problems. Gas leaks were included in this category.
Power-included problems due to a weak or dead battery or power outage.
Recorder-included graphic, digital, electronic data recorder, and timer problems. DCP
problems also were included in this category.
Vandalism and Animal Damage-included human destruction and animal damage.
Oversight-included technician errors such as leaving a graphic recorder pen off the
chart, leaving a timer unplugged, leaving intake or gas valves closed, permitting a strip
chart or digital tape to run out, or incorrectly programming electronic equipment.
These categories are slightly different from those used by Wahl and Shields (Sensor,
Manometer, Timer, Power, Recorder, Vandalism, Oversight, and Other) in their 1989 report. In
the 1987-99 evaluation, the orifice category replaced the sensor category of Wahl and Shields
(1989), the gage-height sensor category replaced the manometer category, and the timer
category was included in the recorder category. The vandalism and animal damage category
included the "Other" category of Wahl and Shields (1989) because most of the other reasons for
missing gage-height record for 1987-99 involved either human vandalism or animal damage of
gaging equipment.
A comparison of the average number of days of missing gage height record for 1971-86 with the
average number of days of missing record for 1987-99 shows an overall decrease of 40 percent.
An average of about 15 days (about 4.1 percent) per year per station for 1971-86 was reduced
to an average of about 9 days (about 2.5 percent) per year per station for 1987-99
(fig. 5). The average yearly
number of days of missing gage-height record ranged from 6.5 to 26.1 days per station for
1971-81 and from 4.7 to 13.9 days per station for 1987-99.
The orifice system used by the USGS has not changed significantly since the 1960's, and
orifice problems continue to be the major cause (46 percent) of missing gage-height record for
1987-99 (fig. 6).
In 1999 alone, orifice problems were the cause of nearly 80 percent of the missing gage-height
data in Kansas (fig.
7). The gage-height sensor caused 29 percent of the missing gage-height record for 1987-99
but was responsible for only 4 percent of the missing gage-height record in 1999
(fig.
8), mainly due to the replacement of manometers with electronic pressure transducers.
An increase in the number of DCP's located at gaging stations across the State from 1982 to
1999 most likely was responsible for most of the 40-percent decrease in missing gage-height
record from 1987 to 1999. DCP's played a major role in decreasing the duration of problems
that caused missing gage-height record. Problems were detected and corrected more quickly
because of immediate access to real-time data from the gaging stations.
There was an increasing trend in missing gage-height record caused by the gage-height sensor
from 1991 to 1994 (fig. 8). The manometer had been the preferred gage-height sensing
instrument used by the USGS in Kansas since its introduction to stream-gaging stations in the
early 1960's. Many of these units still had their original parts, and by the early to
mid-1990's, they began failing. The replacement of manometers with electronic pressure
transducers, beginning in 1993, greatly reduced the number of days of missing gage-height
record due to problems with the gage-height sensor.
The pressure transducer requires less maintenance than the manometer, eventually resulting in
a reduced risk of missing gage-height record due to human oversight. A relatively high
percentage of missing gage-height record due to oversight during 1996-98
(fig. 9) coincides
with the period of the installation of electronic pressure transducers. However, a part of the
higher percentage of missing gage-height record caused by gage-height sensor problems during
1997-98 (fig. 9) can
be attributed to technicians learning the operation of the electronic pressure transducers. By
1999, the amount of missing gage-height data due to oversight was reduced to 0 percent.
The orifice continues to be the largest contributor to missing gage-height record. The
occurrence of missing gage-height record could be reduced considerably with the development of
a viable replacement for the bubbler system. Currently (2001), the development of radar,
laser, and acoustic-doppler devices that can sense gage height or measure discharge directly
without direct contact with the water show some promise.
Continuing evaluation shows the importance of tracking the occurrence and causes of missing
gage-height record to help minimize the loss of valuable information from USGS gaging stations
and to evaluate the effectiveness of improved equipment technology. An annual evaluation of
the data can indicate the need for operational changes, additional training, and research and
development of advanced sensing and recording equipment for the continued reduction of missing
gage-height record. The USGS will continue to evaluate its record of providing high-quality,
impartial environmental data and to seek improvements in data-collection techniques and
equipment for the Nation's benefit.
- Livingston, R.K., 1983, Lost gage-height record in Kansas--its cause and
occurrence: U.S. Geological Survey WRD Bulletin, May-December 1983, p. 52-56.
- Wahl, K.L., and Shields, R.R., 1989, Net gage-height record loss in the Central
Region, WRD: U.S. Geological Survey Hydrologic Instrumentation Facility, Instrument News,
December 1989, p. 12.
For more information, contact:
District Chief
U.S. Geological Survey
4821 Quail Crest Place
Lawrence, Kansas 66049-3839
(785) 842-9909
email: waucott@usgs.gov
http://ks.water.usgs.gov
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