River waves · building, running, surfing

Feasibility study: what is assessed

Every wave that runs today had one. Every project that failed, failed on a question that a study could have asked earlier: Regensburg on the lack of sites, Stuttgart on water quality, Wolfratshausen on costs. The feasibility study is therefore not a paper for the drawer, but the tool with which you decide whether to go on.

Stage 1: Is the site fundamentally suitable?

Hydrology. Discharge data from the gauge over many years: mean discharge, low water and floods, and above all the flow duration curve – on how many days a year does the discharge lie within the window in which the wave would be surfable? In Baden-Württemberg the State Institute for the Environment Baden-Württemberg (LUBW) provides the gauge data. Bern is planning with around 100 surf days a year; below that it gets tight.

Head and geometry. What height difference between headwater and tailwater can be created at the structure, width, bed, banks. This is surveyed (laser scan, echo sounder) – Bern began this way before any modelling was done at all.

Water quality. Bathing water quality at the wave site, discharges upstream, stormwater overflows. See Stuttgart.

Framework conditions. Ownership of banks and weir, protected areas, flood protection, heritage protection, accessibility.

The result of stage 1 is a yes, a no or a "yes, with these conditions". Regensburg had seven sites assessed and did not get an unreserved yes for any of them – that is also a result, and a useful one.

Stage 2: What would the wave look like?

Hydraulic modelling. For one or two variants, it is calculated which construction form (ramp, constriction, impoundment) produces which wave at which discharge: height, width, Froude number, recirculation, behaviour during floods. Today this is mostly done numerically, and for larger projects additionally in a physical model at a university. The University of Innsbruck (hydraulic engineering) developed such models with the wave builder Dreamwave; the Augsburg Technical University of Applied Sciences accompanied the Surfwelle Augsburg in carbon-reinforced concrete.

Cost estimate. Construction, planning, expert reports, operation – with a buffer.

Procedural route. Planning approval procedure (Planfeststellung) or plan permit (Plangenehmigung), authorities involved, timetable. → Ecology and permits

Stage 3: Trial installation at the weir

Between model and construction there is a step that many waves took before they were "built": the trial in the river. The Eisbach wave came about this way – with wooden planks under the bridge, which surfers adjusted with ropes, tolerated for years, legalised in 2010. Salzburg placed a timber ramp in the Almkanal in 2010, around €90,000, and still provides it free of charge today. Pforzheim's first ramp cost about €80,000 plus own labour, and in Nuremberg the Fuchslochwelle began as a ramp idea for €500,000 before it became a hydraulic structure in the course of the procedure. A trial installation answers the question that no model answers completely: does a wave that can be surfed stand at this spot at this discharge?

For Winterbach this is particularly obvious, because structure, banks and access are already there. There is no step – at normal water levels the Rems flows straight through the outlet structure. That is exactly why a trial is revealing: an adjustable board or a small ramp, three to four metres wide, would be the cheapest way to find the shape of the wave and the discharge from which it carries a surfer. The range deliberately extends all the way down: from a single angled, adjustable board at the existing stepping stones, via a timber ramp as in Salzburg, to an adjustable steel element such as Pforzheim is installing in 2026 – costs from a few thousand euros with own labour up to the five-figure range, plus the preliminary hydraulic assessment by a hydraulic engineer. And yes: the trial can become the permanent solution if it shows that a small, adjustable wave is what the site has to offer.

What a trial installation is not: an Eisbach-style start of "let's just put some boards in". The weir in Winterbach is part of a flood retention basin, the Rems a first-order watercourse. A trial needs a temporary water-law permit from the district office (Landratsamt), the consent of the Rems Water Board (Wasserverband Rems) as operator of the structure, a construction that can be removed or lowered during a flood, and a commitment to removal. The stepping stones against which a board would be placed presumably belong to the outlet structure – their function must be clarified before anything is attached to them. That is not an obstacle but the order of things: first the permit, then the trial. → What a river wave costs

Who does this?

Three routes, often combined: a hydraulic engineering consultancy (robust for the authority, costs a five-figure sum), a university with a chair of hydraulic engineering (theses, model tests – Augsburg and Ingolstadt started this way) and a wave builder (Dreamwave, Meo River Concept and others), who offers preliminary assessments but naturally has their own technology in mind. What can be done by volunteers: evaluating gauge data, documenting the site, preparing talks with authorities. What cannot be done by volunteers: the hydraulic proof that the water authority accepts.

And the Remswelle?

We are at stage 1. The project team is gathering the basics: gauge data for the Rems (our own evaluation is available), survey of the weir, framework conditions, talks. As stage 3, we consider a trial installation at the weir to be the right way – small, adjustable, with a permit. We will publish the results on this site as soon as they are robust – even if they are inconvenient. → Project status

Frequently asked questions

What does a feasibility study for a river wave cost?

Documented figures are rare. The city of Regensburg commissioned a site study for seven sites in 2023; the Steyr project is having archaeology, geotechnics and preliminary planning funded through a LEADER project with around €30,000. In our experience, hydraulic modelling with a survey lies in the five-figure range; the exact scope determines the price.

Who prepares a feasibility study?

Hydraulic engineering consultancies and university institutes with experience in wave construction, such as the Unit of Hydraulic Engineering at the University of Innsbruck (Nuremberg, Kempten, Wolfratshausen), DonauConsult (Salzburg) or regional engineering firms such as WALD+CORBE (Pforzheim). The suppliers of wave technology usually provide their own preliminary assessment.

Which data does the study need?

Discharge data over several years (mean flow, low water, floods), a survey of weir, bed and banks, information on the ground conditions, water quality and protected areas, as well as the operating rules of the weir.

Can't you simply try out a wave instead of calculating it?

You can, and many have done so – the Eisbach, Salzburg, the first ramp in Pforzheim. A trial installation with an adjustable board or a small ramp is the cheapest way to find the wave. The prerequisites are a temporary water-law permit, the consent of the operator of the structure and a construction that comes out of the water during a flood.

What happens if the study is negative?

Then the project at the assessed site is over or has to be changed – that is the point of the study. Regensburg had seven sites assessed in 2023 and found none that was suitable without reservation, Wolfratshausen was ended in 2022 because of the costs. Assessing honestly is cheaper than failing late.

Sources: Wikipedia „Eisbachwelle“ (wooden planks, legalisation 2010) · City of Salzburg, „Almkanal“ (timber ramp 2010) · blackforestwave e.V., conversion 2026 · nn.de, 25.03.2022 (Nuremberg: from €500,000 to the full installation) · City of Regensburg, feasibility study Surferwelle, 16.02.2023 · Flusswelle Bern, „Projekt“ (flusswelle.be) · University of Innsbruck, „Die perfekte Welle“ (The perfect wave), 2015 · Augsburg Technical University of Applied Sciences, „Die Surfwelle in Augsburg“ · Surfers Mag, 02.08.2022 (Wolfratshausen) · Stuttgarter Zeitung, March 2019 (Neckarwelle)

Last updated: 15 October 2026 · Initiative Remswelle