Water monitoring for currents and free-flowing reservoirs

Water monitoring can be divided into two main branches: environmental water monitoring, i.e. free-flowing watercourses and reservoirs, and industrial water monitoring, which is intended to monitor flows in industrial or private pipelines. This article deals with the first type of water monitoring.

What does water monitoring consist of?

Water monitoring is the analysis of water availability at a priori fixed locations, conducted at a predefined frequency. The points of interest of the monitoring network are located in the context of the entire water cycle: from water in terms of precipitation (rain and snow) to watercourses (water level in rivers), also considering water storage (natural storage in lakes and aquifers or anthropogenic storage in reservoirs).

The monitoring of all these components aims to provide useful data for environmental protection (e.g. risk mitigation when data show a higher risk of flooding), the planning of future alternative supply systems (e.g. when data indicate a trend towards a dry period) or to manage storage and maximise energy production (which also translates into an economic return).

Another aspect of water monitoring concerns water quality: it consists of periodically collecting quantitative information on the chemical, physical and biological properties of water at predefined locations (chlorophyll content, turbidity level and water temperature).

Who is monitoring the waters?

As already mentioned, water monitoring is of interest to both public entities and private companies. Public entities are interested in monitoring water levels in rivers or reservoirs to adequately deal with flood risk management and prevention; on the other hand, when drought events occur, water monitoring activity helps public entities to assess possible water shortages and contributes to the decision support system for alternative supply.

Private or municipalised companies, mainly in the hydropower sector, monitor the water level in reservoirs and their inflow and outflow. In this case, water monitoring has an economic relevance (it affects energy production), but it also allows hydropower companies to contribute to the risk management of extreme events. In the case of a flood, hydropower reservoirs could store large volumes of water and avoid overflows in the downstream area; on the other hand, in times of drought, water could be released from the reservoirs to make up for water shortages downstream.

How does water monitoring take place?

Depending on the component of the water cycle monitored, different specific instruments are used. For each of these instruments, several types exist on the market; below is a brief list of the main instruments.

  • Precipitation in terms of rainfall: rain gauge (measures the amount of rain in a given time interval per unit of surface area). This type of instrument collects the water falling on it and records changes in precipitation height over time. Figure 1: Rain gauge
  • Water level in rivers/dams: hydrometer, a typically electronic sensor used to measure changes in water levels in a water body (rivers, reservoirs). The water level could also be measured using other innovative techniques involving the analysis of satellite data. Figure 2: Hydrometer
  • Precipitation in terms of snow: Nivometer. This measures the amount of snowfall over a given period of time; it is a special type of hydrometer that measures the depth of the snowpack instead of water. Figure 3: Nivometer
  • Level of wells or water tables: piezometer (measurement of interstitial pressure and water table level) or phreatimeter (measurement of water table level inside open-tube piezometers). Figure 4: Piezometer1.

Why monitor water?

Monitoring activities are meant to address two fundamental aspects: the water balance within catchment areas and/or reservoirs and the prevention and management of extreme events (floods or droughts).

The water balance allows to check whether there are any anomalies within the water cycle that characterise the basin: the input components are rainfall and snowfall, while at the output we have free-flowing runoff, evapotranspiration and possibly infiltration. By monitoring these components, if the input and output should become very different from each other, this could indicate some anomaly and a deeper analysis is required to prevent water supply problems. In addition, the monitoring of catchment water can provide useful data for the estimation of environmental water demands and play the role of decision support for the implementation of relevant legal provisions.

On the other hand, water monitoring allows public entities, but also private companies (e.g. hydroelectric companies), to properly manage any extreme events such as floods or droughts. Water monitoring together with weather forecasts could highlight particular trends, on the basis of which strategic decisions could be made.

When to do the monitoring?

Water monitoring requires constant monitoring throughout the year, as it is not known in advance which periods will be the most critical. However, depending on the ultimate purpose of the monitoring activity or which component of the water cycle is being monitored, the frequency of measurements may vary. In particular, the inertia of the system or the recharge time of the water cycle affect the frequency of measurements: in the case of dams or rivers, monitoring should be constant, i.e. measurements have at least an hourly granularity, whereas for wells or aquifers, as the process is considerably slower, measurements are monthly or weekly.

  1. Sundaram, Baskaran & Feitz, Andrew & Caritat, Patrice de & Plazinska, Aleksandra & Brodie, Ross & Coram, Jane & Ransley, Timothy. (2009). Groundwater Sampling and Analysis – A Field Guide. 2009. ↩︎

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