CHAPTER 6 : SURFACE RUNOFF
Types of streams
1. Perennial streams
This stream always has flow. During dry weather, the flow of the perennial stream is base flow which consists of interflow and groundwater flow intercepted by the stream. Streams that feed from underground water reservoir is called effluent streams. Both perennial and effluent stream are typical of humid region.
2. Ephemeral streams
These streams have flow only in direct response to effective precipitation. The stream does not intercept groundwater flow, so it has no base flow. Streams that feed water into groundwater resevoirs are called influent streams. Both ephemeral and influent streams are typical of arid and semi arid region.
3. Intermittent streams
These streams have mixed charactheristics, acting as perennial stream at some time of the year and as ephemeral stream at other time. Depending on seasonal condition, these streams may feed from or to the groundwater reservoirs.
Flow Measurement
1. Floating Method
A fairly simple method for measuring flow rate through an open channel is the Float method. Although not as accurate as a measuring device such as a flume or a flow probe, the float method can provide an educated estimate.
Briefly put, this method involves measuring the surface velocity of the water with a floating object, and then multiplying this velocity by the width and average depth of the channel.
This method basically apply the discharge equation, Q=Av.
2. Current Meter Method
In this method, the stream channel cross section is divided into numerous vertical subsections. In each subsection, the area is obtained by measuring the width and depth of the subsection, and the water velocity is determined using a current meter. The discharge in each subsection is computed by multiplying the subsection area by the measured velocity. The total discharge is then computed by summing the discharge of each subsection.
Subsection width is generally measured using a cable, steel tape, or similar piece of equipment. Subsection depth is measured using a wading rod, if conditions permit, or by suspending a sounding weight from a calibrated cable and reel system off a bridge, cableway, or boat or through a hole drilled in ice.
Velocity Area Method
The velocity area method is a technique used to investigate the stage and discharge of a river.The discharge of a river is the volume of water which flows through a cross-section in a given time. It is measured in m3/s.
Stream flow is affected by a number of factors including rainfall, temperature and snow melt. Measuring the discharge is important because first and foremost it is crucial in predicting floods. In addition the velocity and flow of a river affects food sources and the migration of fish amongst other wildlife.
1. Perennial streams
This stream always has flow. During dry weather, the flow of the perennial stream is base flow which consists of interflow and groundwater flow intercepted by the stream. Streams that feed from underground water reservoir is called effluent streams. Both perennial and effluent stream are typical of humid region.
2. Ephemeral streams
These streams have flow only in direct response to effective precipitation. The stream does not intercept groundwater flow, so it has no base flow. Streams that feed water into groundwater resevoirs are called influent streams. Both ephemeral and influent streams are typical of arid and semi arid region.
3. Intermittent streams
These streams have mixed charactheristics, acting as perennial stream at some time of the year and as ephemeral stream at other time. Depending on seasonal condition, these streams may feed from or to the groundwater reservoirs.
Flow Measurement
1. Floating Method
A fairly simple method for measuring flow rate through an open channel is the Float method. Although not as accurate as a measuring device such as a flume or a flow probe, the float method can provide an educated estimate.
Briefly put, this method involves measuring the surface velocity of the water with a floating object, and then multiplying this velocity by the width and average depth of the channel.
This method basically apply the discharge equation, Q=Av.
2. Current Meter Method
In this method, the stream channel cross section is divided into numerous vertical subsections. In each subsection, the area is obtained by measuring the width and depth of the subsection, and the water velocity is determined using a current meter. The discharge in each subsection is computed by multiplying the subsection area by the measured velocity. The total discharge is then computed by summing the discharge of each subsection.
Subsection width is generally measured using a cable, steel tape, or similar piece of equipment. Subsection depth is measured using a wading rod, if conditions permit, or by suspending a sounding weight from a calibrated cable and reel system off a bridge, cableway, or boat or through a hole drilled in ice.
Flow Estimation
The velocity area method is a technique used to investigate the stage and discharge of a river.The discharge of a river is the volume of water which flows through a cross-section in a given time. It is measured in m3/s.
Stream flow is affected by a number of factors including rainfall, temperature and snow melt. Measuring the discharge is important because first and foremost it is crucial in predicting floods. In addition the velocity and flow of a river affects food sources and the migration of fish amongst other wildlife.
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