FLOODPLAIN HARVESTING

In New South Wales, the extraction of water from floodplains is controlled by the Department of Industry and Environment, through Water NSW. The whole process is undergoing change to ensure the process is managed in a sustainable fashion which is in turn fair for all water users. Under the new rules, those who take water from a floodplain under license, must measure their take. NSW Water collect the data from all storages and can then aggregate it up to gain a picture for what is happening across a region or catchment.
 

STORAGE VOLUME

Life is simple for farmers who have water delivered to their door in a pressurised pipe. The amount of water used can be measured accurately and economically using any of a wide range of flow meters.
 But where irrigation water is collected from  a river, stream or floodplain and then pumped into an on-farm storage for subsequent use, the picture is far more complex.
 In a swimming pool, with a uniform rectangular shape and vertical sides, it is easy to calculate the quantity of water it contains: multiple the width by the length and then multiply the result by the depth. When the water is in an on-farm storage the principle is the same, but the process is more involved: the sides are not vertical and the length and width change with level.
 The solution traditionally used has been to use a surveyor to accurately measure the profile of the storage, giving the dimensions at specific heights and saving them - along with the amount of water calculated in each slice - in a rating table. The rating table may also be called a storage curve. Rather than rely on traditional surveying techniques, the storage curve can also be obtained using LIDAR.
 In another simplification, rather than rely on a lookup table with hundreds or thousands of lines, the storage curve can be expressed as a formula formulas usually as an exponential equation.

STORAGE METERS

The term Storage Meter is used to describe what is normally  called a water level sensor. But in this application it must be a sensor which can perform at the accuracy required to give a reliable volume figure. Water NSW has a process under which manufacturers can submit their sensors for approval as storage meters. The list of approved storage meters can be viewed on the DPIE web site or on the sites of Irrigation Australia Limited (IAL) and the Australian Hydrographers Association (AHA).
 

Although there are a wide variety of level sensors, those which can offer the accuracy required for use in this application typically come from the following families:
 Radar Level Sensors: these are mounted above the water surface on a gantry or platform. The sensor sends short bursts of high frequency signals down to the water and these are reflected back when they reach the surface.  If the time the pulse takes to travel out and back is measured, it can be used to determine the distance to the water. As wind will create ripples on the water surface, radar sensors must employ averaging to get rid of the noise produced by the ripples: the sensors will take a series of measurements and then take the average.
 Submersible Sensors: these may also be called hydrostatic level sensors. They are installed on the bottom of the storage and employ a pressure sensor to measure the weight of the column of water sitting above the sensor. The pressure can then be converted to an equivalent height. Submersible sensors are not impacted to the same degree by ripples. Regular maintenance is needed to ensure the sensing ports in the sensor do not become blocked.
 Pressure sensors may be one of two different types: vented and un-vented.  Vented sensors have a breather tube which vents to atmosphere, via  a small tube which runs through the cable. The vent ensures atmospheric pressure is applied to one side of the sensor element and water pressure to the other. The difference between the two is the pressure exerted by the column of water above the sensor. This is then converted to an equivalent depth. The breather tube makes the cable bulkier and more expensive.
 Un-vented sensors, although easy to work with, are not permitted under the project guidelines.

LOCAL INTELLIGENCE DEVICES

On its own, the storage meter or sensor is of no use - a bit like having a seat but no car. What is needed is something which can power the sensor, take the level measurement and store it. In the past, this was the job of a data logger. But today, these have been replaced by Remote Telemetry Units or RTUs - which in the language of the DPIE have become a Local Intelligence Device or LID. This unit will have its own power supply to drive the sensor, have electronics to read the sensor and memory to store the readings taken over time. It will then have some communications which is capable of sending the data to a remote computer system for analysis and display.  The most common - and most useful - method for data transmission is to send the data over the mobile telephone network. The computer system to which the level readings are sent, is referred to as the Data Acquisition System or DAS.
 Just as vendors of storage meters must submit sensors for approval against the standards laid down by DPIE, LIDs must too be tested against a set of strict rules. These govern the type of sensors which can be connected, how long the unit can run without charge, how many readings can be stored and how and when they are sent.
 LID vendors can take one of two approaches: firstly by offering an integrated package of LID and storage meter or secondly by offering a flexible LID which can be used with a range of storage meters.
 Regardless of which approach is taken, the LID must be installed by a Duly Qualified Person (DQP) who has been certified as competent by either IAL or AHA.

ML417M1 LID

TOIP has developed its ML417M1 solution as a flexible LID, which can be used with all of the approved storage meters. This approach allows you to sit down with your chosen installer and talk through the process of choosing the storage meter which will work best in your environment. We will then pre-configure the LID to suit that specific sensor.( Download brochure for ML417M1).
 

The ML417M1 is a rugged, reliable unit which takes advantage of our years of experience in the field of telemetry. Power comes from a high-tech lithium iron phosphate (LiFePO4 or LFP) battery. These are typically half the size of an equivalent sealed lead acid cell and, unlike Lithium Ion cells, are completely safe. The battery is charged via a 5W solar panel and is capable of running the unit for 2 months without charge. The heart of the unit is a YDOC ML417 telemetry unit. It’s fitted with enough non-volatile memory (it won’t be lost if the power fails) to hold decades of readings. The unit is fitted with a wide range of sensor interfaces, allowing it to work with any of the sensor technologies used on the storage meters. We build the unit in to a polycarbonate case which is in turn protected from the elements by an aluminium shield. The shield in turn provides a base for the “puck” antenna. Should your site be in a location with poor signal, we can opt for an external high gain or directional antenna

Anyone who has been around for a while will remember the glory days of CDMA, when mobile phones had a range of over 60km. The replacement of CDMA with 3G was indeed a sad occasion for rural communities, as the range to which the service could operate was hard limited to 35km. Whilst the current 4G network is still limited to the same range as the 3G service, there has been one significant development in recent years with the release of the “narrow band internet of things services” which are also called NB IoT. These have been developed specifically for applications like floodplain harvesting and remote metering and have been fitted to every 4G Telstra tower. Whilst the normal 4G data service exists so you can use the internet, watch movies and listen to music while mobile, the NB IoT services are pitched at a different market: for moving small amounts of data for battery power monitoring systems. But while they are sent over the same 4G network as the voice and high speed data services, there is one significant difference: there is no range limit. So if you are on a hill 100km from the nearest tower and have signal, your NB IoT device will work. There are currently two competing NB IoT services: NB1, which offers slightly lower power consumption and longer range and Cat M1. We prefer Cat M1 as it allows us to create a fast, bi-directional communications session to the unit, which is a must for remote firmware and configuration updates. Whilst the service is currently limited to data communications, Cat M1 will be expanded to allow for emergency voice calls and later offered as an alternative for remote users for all voice calls. You can set the units to use Cat M1, NB1 or Cat M1 with NB1 fallback.

OPTIONS

In addition to choice from all of the approved sensors, you can also nominate to purchase your ML417M1 LID with the following options:

- Antenna: Puck (standard), High Gain Dipole, or Directional Yagi

- Lightning Protection: optional module for use in areas with high lightning incidence

- Local Display: this adds a 75mm x 50mm TFT display to the front of the LID and allows you to view the current water level at the push of a button. Press your finger on the level display and it will switch to a graphical view, which allows you to scroll back through the  historic readings.  The display can be added to the standard LID or can be used to make the LID into a Secondary Device, for use in sites with no mobile data network coverage. Historic readings will still be captured in the unit’s memory for access by NRAR, but you can use the display to read the current level at the start and end of a pumping event, so you can enter it in to the portal.

WHERE TO BUY

The ML417M1 LID is available through distributors who have their CSV certification:

AgFlow Solutions       ryan@agflowsolutions.com.au    agflowsolutions.com.au  PH 0400 092 171

Groundwater Imaging     david@groundwaterimaging.com.au     groundwaterimaging.com.au     PH 02 6882 7465

Irritek                        service@irritek.com.au  irritek.com.au  PH 02 6752 6766

Jims Water Metering Solutions      jimsheldrake@outlook.com PH 04 6081 8567

SierraTek                 jcondon@sierratek.com.au     sierratek.com.au     PH 02 6792 5526