Up to two thirds of our drinking water comes from rivers and streams in the US, according to the American Rivers non-profit, a proportion we see across the world. These are the foundation of our civilizations, as well as a key element of virtually every ecosystem around the world. When these are polluted, as it often happens, it's notably in urban areas and developing countries .
Their protection requires a multi-pronged approach: regulatory limits, human testing and enforcement, and autonomous monitoring equipment. The latter is where IoT shines: without any human intervention, accurate and regular readings are collected, analyzed, and provided to the relevant parties for regulation and enforcement.
However, today's monitoring equipment - while heavily used (e.g the metOcean iSphere) - are limited: as they are fixed, they are stuck in a single location in a stream. This limits their effectiveness both in their resolution, as the source of pollution can't be easily pinpointed, and in their deployment ease, as they require time-intensive intervention for deployment and maintenance. We thus are convinced that the full potential of IoT isn't exploited.
Effectively, current monitoring equipment requires human intervention to get higher resolution; frequently, enforcement teams have to take detailed manual readings of water quality, on boats when the river is navigable, on foot when it isn't. Not only is this resource and time-intensive, but it doesn't provide the powerful frequent measurements of the same spot that equipment can give, which reduces external influences and noise.
But what if there was an efficient, low-cost and environmentally-friendly way to monitor the state of our streams and rivers, providing high-resolution and high-frequency readings to the operator, without any human intervention bar deployment and recovery ?
This is SafeStream: a small, geo-tracked instrumented buoy that can be deployed alone or as a swarm, built in rigid polystyrene. These aren't any buoys, these are autonomous free-floating and fire-and-forget buoys.
So, how does it work ? One or more buoys are dropped upstream the river or stream section to measure and recovered downstream. Each buoy is carried by the current, measuring in real-time the parameters via its sensors, and sending them back as well as their positions through a LoRaWAN connection.
When deployed as a swarm, each buoy is dropped at some interval so as to have enough distance between each buoy for their readings to complement each other's, reducing external influences and noise, making for more accurate & robust readings.
Their deployment rarely last more than a month, most often less, as the length of a river rarely exceeds 1000km -but they are able to be deployed for far longer in very long rivers- and speed generally hovers between 1km/h and 10km/h.
The sensors include in the base pack: temperature, turbidity, Ph, salinity and gas (O₂, CO₂, NOX) sensors, and can be extended through sensor packs for specific applications. As the buoy floats and thus descends a stream continuously, relatively high frequency readings are required. These are stored on an on-board flash memory, and when conditions and spectrum regulations permit, transmitted.
As LoRa has a maximum duty cycle and bandwidth, priority is given to the GPS (or similar) location transmission, so as to allow accurate tracking, and eventual recovery. Then, depending on the conditions, frequency of readings and their relative priority to transmit can be configured. If it can't transmit, data is still stored on the flash drive. Once coverage is back, the real-time data is retransmitted as well as - if the conditions allow it - the non-transmitted data.
If a LoRa network isn't already deployed, and regulations permitting, a base station can be mounted on a vehicle following less than 10km away the path of the river or stream, making for maximum availability and flexibility.
The power use estimated is less than than 4W when capturing data, transmitting & receiving continuously, considering less than 1W for the board (see ), less than 1W for TX + RX LoRa communication (see Semtech sx1262 ), and less than 2W for the sensors. For this, we plan to equip the buoy with an on-board battery-pack, rated at 20 000mAh, pre-charged at deployment acts as the main source of energy. This is supplemented by solar panels, of approximately 100 cm², mounted on the buoy, that provides at most 100W (at 20% efficiency, at standard test conditions), which can charge the battery during the day.
All of this allows for a system which monitors in near-real time the water conditions, whose readings are compiled and analyzed in real-time, and where any gross irregularity is directly reported to the operator (such as a government agency), allowing for swift action on their part.
The next steps for us are to refine this project, execute simulations and empirical tests, and build & test a working prototype. In order for this project to become a reality as soon as possible, we need your support. We can all do our part to save our streams and rivers, will you join us ?
: Andrews, M. (1984). Thames Estuary: pollution and recovery.
: See https://www.st.com/en/evaluation-tools/nucleo-l031k6.html
: See https://www.semtech.com/uploads/documents/DS_SX1261-2_V1.1.pdf