Research project DeichSCHUTZ: Reliable measurements for safer waterfronts

Research project DeichSCHUTZ: Reliable measurements for safer waterfronts

In extreme flood situations, the hopes of those people affected lie solely with the dykes – will they hold or not? A dyke failure like the 2013 flood in Fischbeck (Saxony-Anhalt) caused immense damage to inland areas, which continue to have an impact to this day. The active research project DeichSCHUTZ (dyke protection) at the Bremen University of Applied Sciences is involved in an innovative dyke protection system that could prevent failures of this kind.

In Germany alone, river dykes safeguard many thousands of kilometers of waterfront lands. From today’s technological perspective, dykes consisting of three zones are being constructed. The individual zones, viewed from the water-side to the land-side, are built with steadily increasing porosity, thus affording good drainage of the dyke body during a flood event. In Germany, however, many older dykes of homogenous construction do still exist, such as the dyke breached during a flood of the River Elbe in June 2013 in Fischbeck. In contrast to the 3-zone dykes, older ones are particularly vulnerable to prolonged flood conditions. Water seeps into the dyke itself and its saturation line rises further within the dyke body over extended periods of high water. The further this saturation line rises, the more the ground material is subjected to buoyancy. The dyke thus loses its own essential self-mass, required to counteract against the pressure of high water.

Stabilization of a breach-prone dyke requires enormous resources in material and personnel, as well as time, which in acute flood situations is a scarce commodity.  Backup procedures are thus required, which, in terms of personnel, materials and time commitment, are more effective than layering sandbags on the landward side of the dyke.

Innovative mobile dyke protection system

Christopher Massolle of the Institute for Hydraulic and Coastal Engineering at the Bremen University of Applied Sciences is developing a solution that can considerably reduce the input of time and personnel. With the DeichSCHUTZ research project, sponsored by the Federal Ministry for Education and Research, an innovative, mobile dyke protection system is being tested for stabilizing dykes during flooding events. Measurement technology supplied by STS is also playing a role here.

To assess the mobile dyke protection system, a test-dyke has been built on the premises of the Agency for Technical Relief in Hoya. To this end, a U-shaped retention basin holding some 550 cubic meters of water has been constructed, at whose end sits a dyke.

As can be seen in the video, numerous pipes have been deployed at the left side of the dyke. Within these pipes rest ATM/N Level Sensors produced by STS. In the test arrangement, the retention basin is filled with groundwater. Under conditions approaching reality, the water should rise to a level of 3 meters over a period of 30 hours. The submersible level sensor ATM/N  now measure development of the saturation line over this time. With a pressure range from 1 to 250 mH2O and an accuracy of ≤ ± 0.30 %FS (-5 to 50 °C), this is recorded down to the very last centimeter. When the saturation line no longer continues to rise, the mobile dyke protection system is introduced to the water-side slope and should prevent the further penetration of seepage water. The dyke body now continues to drain and the extent of the resulting shift in the saturation line is to be measured by the level sensors employed. It is from these measured results that the functionality of the protection system can lastly be assessed.

Using geomorphometry for hydro-geomorphological analysis in a Mediterranean research catchment

Using geomorphometry for hydro-geomorphological analysis in a Mediterranean research catchment

Abstract

The aim of the paper is to apply an object-based geomorphometric procedure to define the runoff contribution areas and support a hydro-geomorphological analysis on a 3-km2 Mediterranean research catchment (southern Italy).

Daily and subhourly discharge and electrical conductivity data were collected and recorded based on three-year monitoring activity. Hydro10 chemograph analyses on these data revealed a strong seasonal hydrological response in the catchment that were different from the stormflow events that occurred in the wet period and in dry periods. This analysis enabled us to define the hydrochemograph signatures related to increasing flood magnitude, which progressively involves various runoff components (base flow, subsurface flow and surficial flow) and an increasing contributing area to discharge. Field surveys and water table/discharge measurements carried out during a selected storm event enabled us to identify and map specific runoff source 15 areas with homogeneous geomorphological units previously defined as hydro-geomorpho-types (spring points, diffuse seepage along the main channel, seepage along the riparian corridors, diffuse outflow from hillslope taluses and concentrate sapping from colluvial hollows). Following the procedures previously proposed and used by authors for object-based geomorphological mapping, a hydro-geomorphologically-oriented segmentation and classification was performed with an e-Cognition (Trimble, Inc) package. The best agreement with the expert-based geomorphological mapping was obtained with weighted profile and 20 plane curvature sum at different-size windows. Combining the hydro-chemical analysis and object-based hydro-geomorphotype map, the variability of the contribution areas was graphically modelled for the selected event which occurred during the wet season by using the log values of flow accumulation that better fit the contribution areas. The results enabled us to identify the runoff component on hydro-chemograph for each time step and to calculate a specific discharge contribution from each hydro-geomorpho-type. This kind of approach could be useful applied to similar, rainfall-dominated, forested and no-karst 25 catchments in the Mediterranean eco-region.

Read the whole research study.

Source: Domenico Guida1, Albina Cuomo (1), Vincenzo Palmieri (2)
(1) Department of Civil Engineering, University of Salerno, Fisciano, 84084, Italy
(2) ARCADIS, Agency for Soil Defense of the Campania Region, 5 Naples, Italy

Reliable groundwater and surface water monitoring in Romania

Reliable groundwater and surface water monitoring in Romania

A seamless control system with alarm function is required to perform precise water level measurements and to make reliable forecasts on potable water supply, as well as to anticipate floods. Together with its partner MDS Electric Srl, STS has implemented a comprehensive system for groundwater and surface water management in Romania.

Romania draws a major part of its potable water from surface waters such as the Danube, as well as from groundwater resources. A sound management of these natural resources is therefore of huge importance.

To safeguard potable water supply and to protect from flooding, the nation has invested in a comprehensive hydrological measurement infrastructure.

Figure 1: Groundwater measurement point 

In collaboration with its Romanian partner, MDS Electric Srl, over 700 data loggers and more than 350 data transmission systems have thus been installed throughout the country in recent years – also including remote areas. For this reason, the primary investment was in battery-operated measuring instruments, which monitor the current situation on the rivers of the Danube region and also the groundwater resources across the country.

Requirements-specific measurement solutions 

This was a complex undertaking, since each of the submersible probes and data transmission systems deployed required a different assessment and intervention to comply with their respective conditions. An automatic alarm function was also indispensable in this case, should predefined limit values be exceeded.

The permanent monitoring of water levels at important nodes across the potable water supply, as well as the rivers of the Danube region, hinges upon a multitude of requirements:

  • An automated and dependable data transfer via M2M protocol
  • Automatic alarm function when limit value is exceeded
  • Monitoring of water level and temperature, as well as ambient temperature in some instances
  • A server solution with functions for visualizing, evaluating and processing the measured data, as well as the integrated database
  • Easy installation and maintenance
  • On-site support service

For the implementation of this large-scale project, STS opted in pressure and temperature measurements for the DL/N 70 and WMS/GPRS/R/SDI-12 data loggers, or – depending upon requirement – the DTM.OCS.S/N digital data transmitter with Modbus interface to ensure highly precise water level measurement to a 0.03 percent accuracy at critical points.

In association with our local partner MDS Electric Srl, STS was able to realize the entire water level monitoring system from a single source. Each installation point was evaluated on-site by experts from MDS Electric Srl and STS, in order to install a custom solution at each of those individual measurement points. The long-term stability of the pressure measurement technology deployed is also guaranteed. The Modbus transmitter DTM.OCS.S/N excels in this area with an excellent long-term stability of less than 0.1 percent total error per annum. Because of its low energy consumption and robust design, this sensor performs largely maintenance-free for years on end.

Further advantages of the DTM.OCS.S/N in brief:

  • Pressure range: 200mbar…25bar
  • Accuracy: ≤ ± 0.15 / 0.05 / 0.03 % FS
  • Operating temperature: -40… 85 °C
  • Media temperature: -5…80 °C
  • Interface: RS485 with Modbus RTU (standard protocol)
  • Simple implementation in existing Modbus systems
  • Easy adjustment of span and offset
Predicting natural hazards: Level measurement of glacial lakes

Predicting natural hazards: Level measurement of glacial lakes

The glaciers of the Alps are in constant flux. After thawing in the spring and summer, lakes can appear whose levels have to be continuously monitored to detect floods at an early stage. Dependable pressure sensors, level sensors und data loggers are in need here.

The internationally active Swiss company Geopraevent develops, installs and operates high-grade alarm and monitoring systems for various natural hazards, including avalanches, landslides and floods. According to the task and local conditions, the systems are individually designed and implemented. At present, more than 60 alarm and monitoring systems are in use worldwide. When it comes to natural catastrophes, there is no room for error in light of the potentially serious consequences: The technology employed must perform solidly over the years. For this reason, every system is connected to Geopraevent servers to ensure fault-free operation.

Level measurement at the Plaine Morte glacial lakes

This also applies to the system commissioned in 2011 for monitoring the Plaine Morte glacier in the Bernese Alps. As soon as temperatures rise in spring, the glacier begins to melt (see video). From this melting water, three lakes (the Faverges, Vatseret and Strubel) form each year, which then swell constantly over the summer months before finally emptying again.

Danger to the nearby municipality of Lenk, which commissioned the project, arises mainly from the Faverges lake. Like the other two lakes, it exists only in the warmer seasons. After its annual recurrence as a result of snow and glacier melt, the water warms up in the months that follow and then seeks an outflow through the ice. Little by little, this outflow channel becomes further thawed away, meaning that the flow rate constantly increases. In August 2014, for example, some 20 cubic meters of water per second swept down the Trüebach in the direction of Lenk. After emptying of the glacier lake, the cycle will then begin anew the next spring with the onset of the thaw.

To predict a glacial lake breakout and initiate appropriate protective measures, a monitoring system was installed by Geopraevent which ensures an early warning period of one to two days. In the realization of this project, due to outstanding properties of long-term stability and others, STS sensor technology has also been relied upon.

Glacial lake outbreak alarm by SMS

To be able to realistically estimate the danger posed by these glacial lakes at all times, a total of four measuring stations were set up: One each on the three lakes, as well as one on the Trüebach, down which the water flows towards the municipality of Lenk during a glacier lake discharge.

The water level of the three glacial lakes is monitored by means of pressure sensors. To this end, the measuring instruments are submerged into the deepest part of each lake by a helicopter. The level sensors ATM/N/T are connected via a cable to data loggers mounted on a ridge. The data loggers used in this case are solar powered and their collected data is transferred to Geopraevent via mobile telephony. Should the data logger convey dropping levels, this is a clear sign of emptying in the corresponding glacial lake.

Measuring station at the Plaine Morte glacier (Photo: Geopraevent)

Besides lake-level measurement, a level radar also monitors the fill level of the Trüebach. This additional measuring station serves to verify that the glacier lake is also actually emptying out towards the municipality itself. Since the Trüebach passes through a ravine, the level radar is attached to a steel cable stretched across the ravine and is also connected to a datalogger via a cable.

As soon as the pre-defined limit values are undershot or exceeded in the lakes and the Trüebach, those responsible in the community of Lenk are informed automatically by SMS and can then take appropriate measures to prevent flooding.

Polluted sites: Groundwater decontamination requires robust level sensors

Polluted sites: Groundwater decontamination requires robust level sensors

Whether it be old landfills, coal tips, former military sites or refineries, what remains behind is contaminated ground, which is a danger to both humans and the environment. In the rehabilitation of these sites, level sensors are required which are resistant to the often aggressive hazardous substances encountered.

Contaminated sites are not only characterized by adverse health or environmental changes in the soil. In the absence of safety measures (as in old landfills) and depending on soil conditions, hazardous substances are flushed by rain into the groundwater. Depending on the type of usage, a number of different hazardous substances can be found, including, among others:

  • Heavy-metal compounds: Copper, lead, chromium, nickel, zinc and arsenic (a metalloid)
  • Organic materials: Phenols, mineral oil, benzenes, chlorinated hydrocarbons (CHC), aromatic hydrocarbons (PAH)
  • Salts: Chlorides, sulfates, carbonates

Decontamination of the groundwater supply

In the rehabilitation of contaminated sites, not only is cleansing of the soil of great importance, but also the control and purification of the groundwater. Without reliable level sensors that can withstand the adverse conditions, this would not be possible.

The decontamination process usually proceeds as follows: The contaminated groundwater is pumped to the surface and then treated. As filtered flush water, it is next returned to the source of contamination. To prevent this flush water from flowing to a margin away from the contamination source, active hydraulic methods are used for protective infiltration. Water is injected into the ground via several wells situated around the actual decontamination process. The pressure conditions arising here to some extent form a barrier wall and cause the flush water to flow towards the source of contamination. For controlling and monitoring this process, level sensors will be required.

Figure 1: Flow of a decontamination process

Level sensors are of course also used after the remediation work. Long after completion of this work, the affected sites will be monitored to check for any noticeable changes in the water level or the direction of flow.

Level sensors are also used when actively running applications potentially damaging to the environment. Newer landfills are now built like an impermeable basin. The groundwater level below the landfill is lowered, so that no water can flow into adjacent areas in the event of leakage. Here also, the respective water levels are to be monitored by level sensors.

Level sensors in contaminated waters: Highest demands 

Operators in the field of decontamination of polluted sites should be very careful in choosing suitable level sensors. Due to the large number of substances that can be dissolved in the water, there is no single solution that works reliably in every instance. There are several aspects to consider, which we next briefly outline.

Materials

Housing

In most applications, a high-quality stainless steel, as used by STS, is sufficient to protect the measuring cell from aggressive substances. If this were to come in contact with saltwater, then a titanium housing would be chosen, but where galvanic effects are to be expected, a level sensor made of PVDF should be the selection.

Figure 2: ATM/NC chemically resistant level sensor with PVDF housing

Probe cable

Far more critical than choosing a suitable housing, in our experience, is the choice of probe cable. Because of gradual diffusion processes, the progress of destruction is not immediately apparent. Often, this is not visible from the outside even when already damaged. Special caution is therefore required when consulting resistance tables, since these usually say little in particular about probe cables. In the middle of a probe cable is a small air tube, which serves for relative pressure equalization. If the cable material is not one hundred percent resistant, however, raw materials may diffuse through the cable sheath and travel across the air tube into the sensor chip.

Depending upon the substances anticipated, STS users can resort to PE, PUR or FEP cables. The latter can also be used at very high temperatures of up to 110 °C.

Installation

Cable routing

Old landfills and industrial sites are harsh environments, where not only hazardous substances can impair the functionality of the level sensors used. Care must be taken that the cable sheath is not damaged by mechanical burdens (such as debris). Chafing and kinking points should also be avoided. It is therefore recommended to use special protective tubes, such as those offered by STS, when routing cables.

Strain relief

The compression rating of level sensors varies from manufacturer to manufacturer. At STS, all level sensors are pressure-resistant up to 250 meters as standard and their cable is designed for normal tensile strains up to this depth. Nevertheless, operators should consider the use of strain relief in difficult installation conditions.

Mounting

If the sensor is used in flowing waters or tanks with agitators, it can be supplied either with a G 1/2” thread at the cable outlet (pipe mounting) or with a compression fitting (15 mm).

Explosion protection

In applications where a number of hazardous substances are to be expected, it is imperative to also pay attention to explosion protection. Information about this is given by the international standards-compliant ATEX directive.