quantity and quality changes during episodic events. Real-time and continuous
water monitoring programs can provide broader temporal and spatial coverage
than discrete monitoring programs and allow for the collection of data during
times when it is impractical (e.g., night) or dangerous (e.g., during storm events)
to send sampling crews into the field. Some noted applications of real-time water
monitoring technologies include flood forecasting, drinking water source protection, nonpoint source pollution control, ecosystem management, and real-time
response to potentially catastrophic events.
This chapter presents an overview of advances in water sensor and real-time
monitoring technologies. Topics discussed include various types of sensors for
water quantity and water quality measurements, examples of commercially available water quantity and water quality monitoring devices, data collection and
telemetry platforms, and data management and quality assurance/quality control
for water monitoring.
2 Monitoring Water Quantity
Streamflow, also known as discharge, is one of the most commonly reported
parameters in watershed monitoring programs and has origins dating to the late
1800s. Direct measurement of continuous streamflow is not practical. However,
streamflow (Q) can be calculated from parameters that can be measured directly,
i.e., water velocity (V ) and stream cross-sectional area (A). Discrete water velocity
in the stream cross section is measured using a velocimeter. The stream geometry
(depth and width) is also measured at the same points to calculate the stream crosssectional area. From these measures, discrete discharge can be calculated using the
equation: Q ¼ A Â V. In order to estimate streamflow continuously, these discrete
discharge measurements need to be related to a parameter that can easily be
measured continuously such as water level. Measurements of discrete discharge
and water level are made over the entire flow regime in order to establish a good
relationship between stage (surface water elevation above a datum) and streamflow
(discharge). This relationship is known as a stage–discharge relationship or a rating
curve. Once established, a rating curve can be applied to a station to continuously
estimate discharge based on continuously measured water level (stage).
Stage–discharge relationships work well for unidirectional streamflows. However, when there are tidal influences, bidirectional flow or backflow, an accurate
stage–discharge relationship cannot be established by water level measurements
alone, and an index velocity rating needs to be developed. To establish an index
velocity rating, continuous velocity and water level measurements are made with a
deployed velocimeter and water level sensor at a stable location on a stream or
river. Computing discharge using the index velocity method differs from the
discrete stage–discharge method by separating velocity and area into two ratings—the index velocity rating and the stage-area rating. The outputs from each
of these ratings, mean stream velocity (V ) and cross-sectional area (A), are then
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173
water monitoring programs can provide broader temporal and spatial coverage
than discrete monitoring programs and allow for the collection of data during
times when it is impractical (e.g., night) or dangerous (e.g., during storm events)
to send sampling crews into the field. Some noted applications of real-time water
monitoring technologies include flood forecasting, drinking water source protection, nonpoint source pollution control, ecosystem management, and real-time
response to potentially catastrophic events.
This chapter presents an overview of advances in water sensor and real-time
monitoring technologies. Topics discussed include various types of sensors for
water quantity and water quality measurements, examples of commercially available water quantity and water quality monitoring devices, data collection and
telemetry platforms, and data management and quality assurance/quality control
for water monitoring.
2 Monitoring Water Quantity
Streamflow, also known as discharge, is one of the most commonly reported
parameters in watershed monitoring programs and has origins dating to the late
1800s. Direct measurement of continuous streamflow is not practical. However,
streamflow (Q) can be calculated from parameters that can be measured directly,
i.e., water velocity (V ) and stream cross-sectional area (A). Discrete water velocity
in the stream cross section is measured using a velocimeter. The stream geometry
(depth and width) is also measured at the same points to calculate the stream crosssectional area. From these measures, discrete discharge can be calculated using the
equation: Q ¼ A Â V. In order to estimate streamflow continuously, these discrete
discharge measurements need to be related to a parameter that can easily be
measured continuously such as water level. Measurements of discrete discharge
and water level are made over the entire flow regime in order to establish a good
relationship between stage (surface water elevation above a datum) and streamflow
(discharge). This relationship is known as a stage–discharge relationship or a rating
curve. Once established, a rating curve can be applied to a station to continuously
estimate discharge based on continuously measured water level (stage).
Stage–discharge relationships work well for unidirectional streamflows. However, when there are tidal influences, bidirectional flow or backflow, an accurate
stage–discharge relationship cannot be established by water level measurements
alone, and an index velocity rating needs to be developed. To establish an index
velocity rating, continuous velocity and water level measurements are made with a
deployed velocimeter and water level sensor at a stable location on a stream or
river. Computing discharge using the index velocity method differs from the
discrete stage–discharge method by separating velocity and area into two ratings—the index velocity rating and the stage-area rating. The outputs from each
of these ratings, mean stream velocity (V ) and cross-sectional area (A), are then
Advances in Water Sensor Technologies and Real-Time Water Monitoring
173