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WATER LEVEL MONITORING

 

LEVEL MONITORING

 

Water on farms is stored in dams and, in surface irrigation, distributed to fields via irrigation channels. Monitoring the amount of water in dams and the level in channels is a vital component in managing this precious resource.
 

 

LEVEL TO VOLUME

 

Every dam has a profile, which expresses  the cross sectional area at each height. Once this information is known, level or height readings can be converted in to an equivalent storage volume. For dams with a uniform profile (square sides and sloping walls) the calculation is simple; but for more complex structures, a polynomial equation or even a look-up table may be needed. If an accurate water level sensor is installed in the dam, data obtained from the sensor can be used to give a continuous, near real time indication of the storage volume.
 

 

LEVEL TO FLOW

 

Although it is simple to measure flow in closed pipes, it is more difficult to measure flow in open channels or partially flowing pipes. If the channel cannot easily be modified, the flow can be obtained using a combination or depth and velocity sensors. The depth sensor gives height readings which, when combined with the channel profile, give the cross sectional area of water at a given time. The velocity measurement tells how fast the water is moving. The two together give the flow. The accuracy of this type of measurement is dependent not just on the  accuracy of the sensors but also on how  accurately the  channel profile can be measured.
Where the channel can be modified a V-Notch weir can be installed. The geometric design of the notch ensures that the flow through the weir is directly proportional to the flow of water through it. So a single level sensor can be used to monitor flow.
 

 

CHANNEL HEIGHT

 

Surface irrigation systems rely for their proper functioning on the strict control over height.: water is pumped from the ground (bores), a stream or from captured overland flow, in to a storage dam. It is kept there until required for irrigation. Water is then released from the dam in to supply channels and then, via a system or gates and valves, delivered to field channels. Getting the right volume of water to  the bay, so that it can advance at  a rate which maximises infiltration and distribution without losses from drainage or runoff, is dependent on maintaining the right “head” or height of water. If the channel level gets too high, there is a risk of spillover, with water over-flowing the channel walls, leading not just to water loss but potentially to damage to the channel walls. The flow which can be obtained from a given pipe is a function of the diameter (and hence cross sectional area) and the pressure of the water.  If the channel level falls, the pressure or head (which is a measure of its height) may be too low to maintain the required flow.  If the flow falls, the advance rate falls, reducing the system’s ability to deliver water efficiently.
 

 

WATER LEVEL RTU

 

The YDOC MLN315ADSPV is the ideal base for a water level monitoring station for dams and channels. For bore hole monitoring, check out the WDL315. The Mln315  can be connected to a wide variety of level sensors, the most common of which are the hydrostatic level sensors. These convert the pressure exerted by the column of water into an electronic signal which is in turn fed to the telemetry unit. To avoid “noise” caused by ripples on the water surface, the sensors are normally installed in a stilling well.
 

 

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The telemetry unit is mounted within a shroud which is fixed to a stainless steel post. The shroud protects the unit from damage during transport and storage. A gauge board is fitted to the base of the pole allowing quick visual checks of the level to be made. The level sensor (a hydrostatic pressure sensor) is fitted inside a stilling well. To install the unit, a post is permanently installed in the channel. The level monitor can then be sleeved on to the post. Installing multiple base posts allows the one monitor to be shifted from channel to channel as they are brought in to use. Readings from the RTU are sent via the mobile data network to a server and can be viewed on any web compatible device. Alarms can be set on the unit and an SMS sent  to 1 or 2 pre-programmed mobile phones if the level goes above or below the preset limits. The telemetry unit can be accessed remotely, enabling suitably trained staff to change the alarm levels without needing to visit the site
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