Rapid Deployment of Hydrological Monitoring Station
Following a 3.2 magnitude earthquake on September 7th, the water level of the karst river Vrljika started dropping very quickly. This rare phenomenon has last occurred in 2004, and, before that, in 1942. Low water levels of Vrljika can be dangerous for several endemic fish species; and the whole Imotski region gets its water supply from Vrljika. Less than 24 hours after the event, Geolux technicians had installed a remote water level monitoring station to monitor water levels of Vrljika in 5 minute time intervals.
Geolux has installed its integrated hydrological monitoring station consisting of a radar-based water level sensor (LX-80-15), a surface velocity radar sensor (RSS-2-300 W), a SmartObserver datalogger with integrated GPRS modem and battery charger, a 10 W solar panel and an 8 Ah backup battery. Using an integrated station which relies solely on non-contact instruments allowed Geolux to setup the station in less than 2 hours, giving an extremely short response time to a critical situation.
Discharge Measurement on Small Channels
To monitor water discharge on a small stream, Geolux has installed HydroStation - highly integrated hydrological monitoring station that consists of radar-based water level sensor, surface velocity radar, Lithium battery pack, solar panel, Geolux HydroCam camera and GPRS datalogger. The station is installed on a bridge above the channel, to measure water level and total discharge. The measurement site is specific because on such a small channel, expected discharge is very small. To improve discharge measurement when the water level is very low, we ave installed additional V-notch weir. This channel is used for irrigation of a nearby field, and the study that uses Geolux instruments aims to determine if more fields can use the same channel for irrigation, or additional construction work will be required.
The main benefit of using Geolux instruments on this site is simple and quick installation. HydroStation comes pre-installed with all instruments and solar panel already attached, and on-site installation requires only attaching the station to the fence that exists on the bridge. The calibration for discharge measurement is also easy, as the channel below the bridge is rectangular and made from concrete. Geolux HydroCam is used to take images of the staff gauge for redundancy, and to provide visual information about water icing or aggregation of driftwood and garbage.
Measured data is transmitted to Geolux HydroView cloud-based software, that stores it in an internal database. HydroView provides a user interface that allows users to monitor hydrological data in real time. HydroView also allows the users to setup and remotely re-configure the operating parameters of a SmartObserver datalogger, and to remotely change the operating parameters of hydrological instruments that are connected to the datalogger. Integrated in HydroView software is a water discharge calculation module. This software module calculates water discharge based on indirect measurements of water level and surface velocity in one or more points on the river profile. If surface velocity radars are not present on-site, discharge can be calculated using a predefined Q-H curve. Or, if a V-notch is used on-site, the V-notch parameters together with the water level are used for discharge calculation.
Monitoring Station at Lazina, Croatia
Geolux has recently installed an automatic hydrological monitoring station at a location in Croatia. The monitoring station is based on a compact Geolux HydroStation system. It consists of a radar level sensor LX-80, a surface velocity radar RSS-2-300W, a HydroCam camera, SmartObserver datalogger, a 20 W solar panel, and a 20 Ah lithium-ion backup battery. All instruments use contactless methods for making measurements, and the equipment is mounted on a bridge over the waterway. The complete installation and setup procedure took less than 30 minutes on-site.
The monitoring station was configured to measure water level and surface velocity every 15 minutes, while the attached camera was configured to take a photo every hour. The measured data is uploaded immediately to Geolux HydroView on-line service using a GPRS modem that is integrated with the SmartObserver datalogger.
Off-Grid Power Supply
Under normal operating conditions, a solar panel provides power to all instruments during the daytime, and the backup battery provides power during the night and under low-light conditions. The solar panel is large enough to provide sufficient power both for the operation of all instruments and for battery recharging. The battery charger circuit integrated into SmartObserver datalogger uses the MPPT technique to maximize power extraction, even when the solar panel is not exposed to direct sunlight.
The backup battery that is used inside HydroStation was carefully selected to meet several requirements. The battery must have a high cycle life and lifespan to provide stable power over prolonged periods and to minimize maintenance costs. The battery should be safe to operate. The battery capacity must be sufficient to provide the power to the instruments and the data logger during longer periods when the solar panel is not producing electricity. After comparing and testing multiple different types of batteries, we have decided to use a lithium-ion battery - more specific, LiFePO4 battery.
The solar panel can stop producing electricity for a multitude of reasons. Iz Zagreb, where Geolux office is located, it is common to have thick clouds obscuring sunlight for a few weeks during the winter. Severe air pollution, fog, and smoke from wildfires also obstruct solar panels from producing electricity. Snow can accumulate on the solar panel for weeks and completely block the sunlight. And finally, the solar panel can fail, the cables between the solar panel and the battery charger can be ripped or torn, or the solar panel can be vandalized or stolen.
The battery capacity was selected to ensure autonomous operation for at least 30 days, even without the solar panel attached. Having 30 days of battery autonomy is enough when the solar panel gets temporarily obstructed, and in case of complete failure of the solar panel, it gives enough time for the servicing team to arrive on location and repair or replace the solar panel. We have calculated that a battery with a capacity of 20 Ah can provide power for at least 30 days of operation of all instruments, with 15-minute readout intervals.
Running the Test
After installation of all equipment, we have decided to run an actual test of battery autonomy. The battery was fully charged before the test, and the solar panel was disconnected from the battery charger. We have continuously monitored the battery voltage over time. The test was run for 30 days.
We have started the test on April 7th, with the battery voltage at 13.82 V, which corresponds to a 100% charge. The test was completed on May 7th, with the battery voltage measured at 12.86 V, which corresponds to 19% charge capacity. A 20 W solar panel was reconnected to the battery charger at 10:00 AM, and the battery was recharged back to the full capacity by the end of the day.
After reviewing the test data, we have concluded that 20 Ah LiFePO4 battery comfortably supports the 30-day autonomy of a Geolux hydrological station. All instruments were operating correctly, even when the battery capacity dropped below 20%. Recharging a battery from 20% capacity to 100% capacity on a sunny day took no more than 10 hours.