Probleme bei Planung und Betrieb von Absetzbecken für Straßenabwässer

Sedimentation basins are incorporated into runoff infiltration systems and serve as a retention system, in which the sedimentation of particles occurs as a result of gravitational force. The effectiveness of sedimentation basins in terms of removing particles is highly dependent on design parameters such as their dimensions and drainage times. To evaluate the flow distribution within sedimentation basins, a conceptual model was developed using a tracer and compared to the actual condition at the treatment system. Here, a significant difference in the height of the connecting tube between settling basin and filter basin was found. This leads to a drying out of the basin, which significantly affects the flow rates and hence the sedimentation there. Based on a model experiment with colour tracer, the flow paths were visually represented in the basin, and both the concrete variant and the effects of internal structures were considered. It was found that the incorporation of a baffle led to an improved utilization of the basin, and to water being retained for longer times. Due to the lower flow rate and these longer times, fine and medium-sized sediments could be easily settled. In a field study, the performance of a sedimentation basin for the removal of particles was evaluated based on the influent and effluent concentrations of total suspended solids (TSS). The street runoff treatment plant was monitored for one year and results showed that there was no particle accumulation in the sedimentation basin (there was no permanent retention of the particle loads). The mean TSS concentrations were 89 mg/L at the inlet of the sedimentation basin and 94 mg/L at the end of the settling tank, respectively. The structural design and operation of the system showed higher flow and turbulent flow conditions in the sedimentation basin, in which settlement of fine and medium sized particles was very low; as a result, the soil filter basin was loaded with runoff particles. Thus the particulate matter had to be removed either on the surface of the filter basin or within the porous space of the filter. The build-up of such particles can result in a significant increase of head loss due to clogging; therefore, filters must be maintained by removing the accumulated particles on a regular basis.     

Die Bedeutung von Feststoffhaushalt und Sedimentdurchgängigkeit für eine nachhaltige Nutzung der Wasserkraft

The sediment regime and continuity in rivers are essential considerations from both river engineering and ecological standpoints, as can be seen e.g. in the problems concerning the riverbed degradation of the Danube east of Vienna. The imbalanced concentration of solids is caused e.g. by disruptions in flow, which include weirs and the reservoirs of hydroelectric power plants. In this context, the latter are above all affected by the problem of reservoir sedimentation, which can be detrimental to both energy production and flood protection. In order to counteract this sedimentation, measures are undertaken in the catchment area, in the reservoir or at the damming structure, which have to be optimized regarding their effectivity. In this regard, experimentation involving physical models, one-dimensional and multi-dimensional sediment transport models is becoming increasingly popular. Key questions that arise here concern the quality and availability of necessary measurement data, as well as the choice of model, and generally speaking a number of research questions remain open. From an ecological standpoint, a gravelly riverbed substrate is vital to the reproduction of certain fish species, which explains why the question of sediment continuity needs to be taken into account when new hydroelectric power plants are to be built or older ones are to be renovated. The (Austrian) national project SED_AT and the EU project SedAlp are currently working to identify key problems and research needs. One proposed approach is based on integral water resource management, in which the technical, economic and ecological optimization of reservoir management addresses the needs of the various stakeholders on the one hand, and includes the broad range of relevant natural processes (erosion, transfer, sedimentation, remobilization) on the other.     

Erfassen von Ursache-Wirkungs-Beziehungen in Flusslandschaften: Vermittlung von Systemwissen in Schulen als Beitrag für ein nachhaltiges Flussgebietsmanagement

A scientific understanding of the processes at work in river landscapes represents an important basis for including the local populace in effective and sustainable river landscape management. By conveying system-based knowledge to students, these future inhabitants and users of river landscapes will be better able to recognize contexts and connections, understand project-related decisions and policies, and support sustainable planning efforts. As such, in October 2012 the Austrian Federal Ministry for Science and Research started the “FlussAu:WOW!” project, part of the “Sparkling Science” research program. In the project, scientists work together with the students from two upper-level high-school classes over a period of two years, investigating research questions on river landscape management. The scientific goal of the project is to create a set of indicators to represent the functionality of floodplains. In the first school year, the researchers worked on key questions together with the students in workshops, performed field surveys and analyzed the results of fieldwork. In the subsequent discussions, the researchers constantly pointed out the complex interrelations at work in river-floodplain systems. Students’ knowledge was evaluated in pre-project and post-project tests. The analysis of the pre-tests revealed major knowledge gaps on questions concerning river landscape management, e.g. on factors that place major pressures on these regions. A comparison between the pre- and post-tests confirmed a significant improvement in the students’ factual knowledge after the first year; however, the post-project tests only showed a coupling of that knowledge with a recognition of cause-and-effect relations in sporadic cases. Beyond factual knowledge, it is above all a grasp of the interconnections between individual system elements that serves as an essential basis of education. Interactive, modern approaches are critical to conveying interdisciplinary knowledge. As part of the “FlussAu:WOW!” project, in the second school year system-based learning is implemented with the help of innovative modeling and simulation software. In both the pre- and post-tests, questions on the students’ interests revealed a high level of motivation to join in the research, and considerable interest in questions concerning nature and the environment. As a result, by the end of the first school year the cooperation between researchers, educators and students had already made a valuable contribution to sustainable river landscape management.     

Innovative Kanalinspektion als Grundlage für die bedarfsorientierte Kanalreinigung

Today, there are roughly 100,000 kilometers of actively used public sewer pipes in Austria, making effective sewer cleaning one of the most essential responsibilities of sewerage providers. Unfortunately, given the precarious financial situations faced by many cities and communities, sewer cleaning also means a considerable financial burden. As a result, many of them have had to extend their maintenance intervals or postpone much-needed cleaning procedures. In response, ÖWAV Rule Sheet 22 (draft version from September 11, 2012) recommends taking a proactive approach to the operation of sewer facilities: “Forward-looking management and maintenance planning help to ensure facilities’ smooth operation and reliable waste removal, while also minimizing maintenance costs and negative effects on the environment.” However, the prerequisite for this forward-looking management is a precise knowledge of the sewer network in question. A fast and simple method for arriving at an overview of a sewer network, how clean or dirty it is, and the thickness of accumulated deposits in comparison to the cross-section is e.g. inspecting it with a manhole camera (electronic sewer inspection). A case study of efforts implemented in the city of Salzburg show the savings potential offered by using forward-looking management in connection with sewer cleaning.