Overview
The NexSens RiverGage is a real-time water level and flood alert system based on cutting edge radar sensing technology and reliable data logging. This downward looking system provides quick and easy (on-bridge) installation with no need to enter the water. Eight D-Cell alkaline batteries can power the system, or an optional solar power pack can be integrated for continuous, long-term operation.
A sampling rate of 16 Hz (16 measurements/second) with 20 second averaging minimizes water surface conditions, such as waves and turbulence. The RiverGage sensor is unaffected by air temperature, wave action, humidity, flood events, floating debris, or contaminated water. This highly accurate measurement method meets United States Geological Survey (USGS) guidelines for water level detection and provides drift free performance. Discharge (flow) can also be calculated based on manually entered stage/discharge rating data.
The RiverGage real-time flood alert system consists of a NexSens SDL500C submersible data logger with cellular telemetry, NexSens lockable aluminum Utility Box, and OTT RLS radar level sensor. The system can be configured for use on any of the major cellular networks, including Verizon, AT&T, or Sprint/Nextel.
Radar Level Sensor
The RiverGage's radar level sensor technology is based on impulse radar. Two antennas are enclosed in a compact housing and transmit pulses toward the water surface, through a Teflon face plate. The transmitting antenna transmits short radar pulses in the 24 GHz ISM band. The receiving antenna receives the pulses reflected from the water surface to determine the distance between the face plate of the radar sensor and the water surface. The time delay from transmission to receipt is proportional to the distance between sensor and water surface.
Historically, radar level sensors have not delivered the same accuracy as bubbler sensors or pressure transducers; however, the RiverGage radar level sensor uses a revolutionary non-contact level measurement technology, offering the USGS accuracy requirement of +/-0.01 feet. With a non-contact measurement distance range of 115 feet to water, the RiverGage is a solid choice when a bridge or above-water structure is available for mounting.
Selecting a Location
To obtain reliable and correct water level measurements, there are some boundary conditions and installation guidelines that should be observed. The radar level sensors should be mounted directly above the water surface, such that the radar beam is perpendicular to the water. The overall system installation requires secure mounting to prevent vertical displacement by wind or vibration. Any movement disturbs measurements and can result in vertical alignment errors.
To minimize the influences of wave action, the water surface must be as smooth as possible in the area of the sensor beam. Avoid submerged obstructions such as rocks or bridge piers that disturb or influence the water level. It is also important to check for any obstructions that could surface when the water is at the lowest anticipated level.
Bridges and other large structures have a tendency to expand and contract with temperature. The bridge height can change several inches with diurnal temperature changes. Trucks and other traffic loads can cause transient changes to the bridge height which affects water level measurements. To minimize these effects, the radar level sensor should be mounted near a bridge support point or a pillar.
Alarm Notification
NexSens RiverGage Flood Alert systems offer two types of alarms; software and data logger. Software alarms are used to notify persons via SMS text messaging or email of parameters exceeding pre-defined limits. NexSens iChart Software sends the alarm when it receives data from the data logger. Data logger alarms are used to change the functionality of the data logger based on parameter inputs, such as changing sample and log intervals based on a particular logged reading.
Once the water level alarm limit is determined, the value is entered into NexSens iChart Software. When the water levels exceed this pre-defined range during rain events, a text message or email is automatically sent to a pre-defined list of contacts to take appropriate actions. Typically, this involves notifying nearby residents and closing off roads that may be affected.
Managing Data
Water level data is logged at a user-defined interval (minimum 1 minute). The user also sets the interval at which data is transmitted via cellular telemetry. A common interval for flood alert systems is to log water level data every 10 minutes and transmits data every 30 minutes. Water level data is transmitted over a cellular network to a remote computer. To receive data, all that is required at the remote computer is iChart Software and an Internet connection.
iChart is a user-friendly Windows-based software package that serves as the centralized interface and database for all incoming data. A single Software license can manage a virtually unlimited number of remote flood alert sites. The software allows users to generate customized reports with water level data from all systems in an iChart database. Reports can be converted to PDF, exported to Microsoft Excel, sent to interested parties via e-mail, uploaded to a web server, and more.
NexSens WQData PRO is an optional web-based data management solution for flood alert systems and other environmental data. The modular datacenter interface can be easily customized to include project-specific themes and information. WQData PRO offers a unique Active Data Sourcing tool that allows users to query and include water level data from USGS gaging stations, National Weather Service sites, and other publicly available datacenters.
System Maintenance
The RiverGage non-contact level measurement system can be powered internally by eight D-cell alkaline batteries or by an external 12VDC regulated power source. When the NexSens RiverGage system is internally powered, periodic maintenance is required to replace batteries. This maintenance interval is dependent on many variables including sample/log interval, cellular transmit interval, and operating temperature.
To significantly reduce the need for site visits, the system can be continuously powered by NexSens 5, 10, or 20-watt solar power packs. NexSens Solar Power Packs consist of a solar panel, built-in charge regulator, and 8.5 A-Hr sealed lead acid battery housed in a watertight enclosure.
The radar level sensor is nearly maintenance-free. The sensor does not require calibration, and there are no parts that need replacing regularly. Periodic site visits are helpful based on local conditions for preventative maintenance. When visiting the site, the user should check the radar level sensor for dirt, spider webs, or insect nests on the sensor. If fouling exists, the sensor can be cleaned using a gentle cleaner and soft sponge. The user should also check for obstructions in the measurement beam, including tree branches that could distort the measurement.
Rental Equipment and On-Site Services
Water level and flood alert systems are most commonly purchased and installed for long-term or permanent applications; however, there are commonly short-term level measurement and flood alert applications that make it cost-prohibitive. NexSens Technology offers both standalone and real-time cellular telemetry RiverGage Systems with weekly and monthly rental rates to meet project requirements.
To ensure that customers can begin using their RiverGage Systems as quickly and efficiently as possible, our application engineers are available for training and technical support, both by phone and in person. Our company offers both extensive field experience and a wide array of deployment hardware to facilitate seamless implementation of the project. Contact our application engineering team for your next water level monitoring or flood alert project.
