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Harbinger

CASE STUDY

Kumeū Flash Floods

30-31 August 2021

According to NIWA's Monthly Climate Summary for August 2021, "Kumeū (West Auckland) received 201 mm of rain during a 14-hour period from 30-31 August. The daily total of 208 mm represents 149% of the normal August monthly rainfall total at Kumeū.".

Extreme flooding occurred in places that were never inundated before, at least not to living memory.

There were no warnings or news bulletins to alert residents and businesses about the risk of abnormally high rainfall and the impending disaster.

The heavy rain fell in the dark, up in the catchment area of the Kumeū river, while most people were asleep.

The water formed overland flow paths where no-one in living memory ever saw flowing water during previous floods.

One of the residents, for example, woke up when the power in his residence tripped out. Mains power was still available but the RCD prevented a restoration to some circuits. Upon investigation he discovered that his house was surrounded by rising flood water - eventually breaching and running through his house. Several neighbouring houses and properties suffered similar devastation. Some animals drowned while others were saved by their owners.

The combined damage to businesses and residences in the area was estimated to be in the millions of dollars.

27 January 2023

Sadly, with climate change and more energetic weather systems a flood, like the one described above, happened again on Friday 27 January.

At the time, NIWA wrote on twitter: "We can confirm that Auckland, Kumeu has observed 79% of its normal *summer* rainfall in just 15 hours today (166 mm)."

However this time the whole upper North Island including larger Auckland and the Coromandel was devastated by the weather event and floods.

Just like with the August 2021 event, there was no advance warning for the January 2023 event.

If people had received some advance warning, even if it was less than an hour, before a flash flood, they could have taken steps to protect their valuable possessions, move their vehicles to higher ground, and evacuate the area to avoid being caught in the flooding.

13-14 February 2023

Cyclone Gabriel barrelled down the east coat of the North Island with strong winds and heavy rain over several days.

Similar flooding and devastation was expected in Auckland, but the rivers did not rise to the same levels as during the two evens described above. People were alerted through media channels which allowed people to prepare for the expected flooding.

The Coromandel, Bay of Plenty, East Cape, and Hawkes Bay suffered utter devastation. Many people were surprised and overwhelmed by severe flash flooding that trapped people and destroyed homes and infrastructure.

HARBINGER - FLOOD EARLY WARNING SYSTEM

An affordable early warning system is now available to provide flood alerts based on the water level at strategic points in a river's catchment area or that of a stream.

The system uses building blocks linked together to provide the necessary surveillance for a specific application scenario.

The basic building blocks of the surveillance system are field terminals and base stations.

A simple installation consists of a field terminal communicating with a base station. (i.e. A 1-to-1 configuration.) In this configuration, the system can operate autonomously without an Internet connection. However, when connected to the Internet, the collected data is logged remotely, and flood alerts can be relayed to a broader audience. (Using, for example, Twitter or other platforms.)

Multiple field terminals can also communicate with one base station. (i.e. A many-to-one configuration.)

More complex configurations are possible where single-terminal and multiple-field-terminal installations share information via the Internet.

Where base stations are connected to the Internet, the gateway to the Internet must be connected to battery backup to ensure that it will remain operational during power outages.

A block diagram of the simple 1-to-1 installation is shown below:

Field Terminal Attributes

The battery-powered field terminal is typically mounted on a pole or other structure where it cannot be submerged during a flood. The field terminal is equipped with a solar panel and a charge controller to maintain battery power. The primary purpose of the field terminal is to measure water level, and different types of level transducers can be used with the field terminal. The low-cost version of the field terminal is supplied with a floating arm equipped with an angle sensor. As the float follows the water level, the boom angle changes, and the angle is converted by the field terminal to a the medical value in reflecting the water level. In cases where the floating arm cannot be used, the more expensive submersible pressure transducer can also be used to measure the water level.

The field terminals also equipped with a rain gauge, which can be excluded if not required for a specific application. A tipping bucket rain gauge provides valuable rainfall information in addition to the water level.

The field terminal also transmits the battery voltage and the enclosure door switch state to the base station.

The field terminal communicates with the base station through a LORA transceiver.

Field Terminal Specifications

Radio technology used: LORA Transceiver. Tx power 100mW

Parameters: 3 Analogue equivalent, 4 digital

Update rate: Programmable (On the default setting it will send a data packet every 5 minutes and instantaneously for a level change larger than 20mm since the previous transmission, and also every 30s for 5 minutes after a level change larger than the threshold value.

Rain gauge: Tipping bucket

Level sensor: Accelerometer (Angle sensor) or optionally a pressure transducer.

Resolution: bits/mm increases with water level. (Sin θ where 0° corresponds with a horizontal boom and approx. 45° as show in the photo.)

Accuracy: Depends on engineering unit conversion equation and EUC parameter values used.

Repeatability: Very high, with ± 1 bit noise deviation.

Range: Dependent on radio path. (Antenna type, height, terrain and obstacles. Line of sight) Typically, 3km.

Power: 10W solar with MPPT controller

Battery: 2 x 12V 7Ah

Base Station Attributes

The base station is battery powered. The battery is charged through a mains-powered adaptor. In the absence of a mains power supply, a solar panel with a charge controller can be supplied with the base station.

The base station has a programmable processor and is equipped with a LoRa transceiver, Wi-Fi, and a wired Ethernet connection. The base station can be interfaced to the Internet for data logging, but doesn’t rely on the Internet connection for local alarms.

The base stations is also equipped with a visual and audible warning will be activated when a pre-programmed water level has been exceeded.

Base Station Specifications

Enclosure: ABS enclosure with a hinged door

Dimensions: 290mm x 190mm x 140mm

Power source: 12V 7Ah Battery maintained by a Mains Powered Charger

Radio: LORA Transceiver 100mW transmitter power.

Antenna: Omnidirectional with SMA connector. Location must allow for a reliable radio path to the Field Terminal.

Outputs: Visual alarm indicator and audible warning sounder mounter in the enclosure with dry C-form relay contacts to drive a remote Audible and a Visual Alarms

External Connection: RJ-45 Ethernet Connection for connection to an Internet Gateway

Sample of a Level graph. (Depth in mm against time)

Internet Connection

Although the internet is not required for system operation a base station can it log data to the ThingsSpeak from where the data can be accessed and presented to subscribers. Tweets can be generated on pre-programmed conditions like when the battery voltage is low, or when a certain water level is exceeded.

Interfacing to other online platforms is also possible and can be implemented as a variation on request.

ThingSpeak is an application for IoT projects for data collection in the cloud with advanced data analysis using MATLAB. ThingSpeak and MATLAB are trademarks from MathWorks.

ADAPTABILITY

Adaptable to warn about impending landslides too!

The field terminal can be configured to detect ground movement. The detector can be installed on a slope below a property built close to a terrace or perhaps above a property that could be inundated by a landslip.

Even seconds count and could save lives.

Please contact us if you would like to discuss a particular application by sending an email to harbinger@debulec.co.nz

DISCLAIMER

The system utilises affordable consumer-electronics components to ensure its affordability. Consequently, guaranteeing its safety integrity level would be difficult. Nonetheless, it is crucial to emphasize that despite its limitations, this system is far superior to having no means to provide advanced warnings.

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