ECOHYDRAULICS

Welcome to the Ecohydraulics community website

Fri, 29 May 2026 00:00:00 GMT

Welcome to the online home of the Ecohydraulics community! This website brings together the people, ideas, and resources that connect researchers and practitioners working at the interface of ecology and hydraulics around the world.

What you'll find here

About - the history and organization of the community and the IAHR Ecohydraulics Technical Committee.
Community - conferences, awards, jobs, allied organizations, including the Early Careers on Ecohydraulics Network.
Education - courses, workshops, training, and learning resources.
Research - the Journal of Ecohydraulics and a software guide for the field.

Get involved

This site is from the community, for the community. If you have content, events, job postings, resources to share, or a viewpoint on what ecohydraulics is: we'd love to hear from you. Follow us on YouTube and LinkedIn to stay up to date.

New Ecohydraulics Interview: Andrés Vargas Luna - Vegetated Rivers

Thu, 30 Apr 2026 00:00:00 GMT

Andrés Vargas Luna — Vegetated Rivers

We have another interview video up on the Ecohydraulics channel, giving a short glimpse into the people, ideas, and river-brain behind the field. No need to overcook it: grab a coffee, hit play, and enjoy a compact dose of ecohydraulic conversation without drowning in slides, equations, or conference-room oxygen depletion.

New Ecohydraulics Interview: Knut Alfredsen - Cold Rivers

Thu, 30 Apr 2026 00:00:00 GMT

Knut Alfredsen Interview: Cold Rivers

The Ecohydraulics video channel has landed another interview, this time with Dr. Knut Alfredsen from the Norwegian University of Science and Technology (NTNU). If your scientific comfort zone includes hydrology, hydropower, cold-climate rivers, habitat modelling, and the occasional icy field problem that refuses to behave like a textbook example, this one is worth a coffee break. So, those teaching, modeling, restoring, licensing, or simply trying to understand what rivers are doing while pretending to be predictable, check out the interview. It may not solve every Pandora's box in ecohydraulics, but it certainly opens a few worthwhile drawers.

International Symposium on Ecohydraulics (ISE) 2026 / Lausanne, Switzerland - Update: Early-bird Deadline Extended

Thu, 30 Apr 2026 00:00:00 GMT

Early-bird deadline extended: more time to sort your Lausanne plans

Good news for everyone still wrestling with travel forms, budget approvals, train tickets, flight prices, hotel tabs, institutional portals, or the general admin swamp that comes with conference season: the early-bird registration deadline for the Ecohydraulics conference in Lausanne has been extended to May 15.

Registration is available here: https://ise2026.epfl.ch/registration/

So, if Lausanne is on your summer map, this is the moment to lock things in. Presenters, poster people, session-hoppers, river nerds, model wranglers, field-data survivors: get registered, sort the travel, and we will see you by the lake.

Gregory Pasternack Appointed Editor-in-Chief of the Journal of Ecohydraulics

Fri, 16 Jan 2026 00:00:00 GMT

Prof. Gregory Pasternack (University of California, USA)

Gregory Pasternack, Professor of Watershed Hydrology at the University of California (USA), is appointed new Editor-in-Chief of the Journal of Ecohydraulics!

This appointment follows an open and competitive selection process led by IAHR. Prof. Pasternack was chosen for his strong scientific track record, clear editorial direction, and longstanding engagement with the ecohydraulics community.

The community extends sincere thanks to the outgoing Editor, Takashi Asaeda, for his dedicated leadership and contributions to the journal's continued growth and success.

Journal of Ecohydraulics

On accepting the role, Prof. Pasternack highlighted a practical, author-supportive editorial approach aimed at strengthening the quality and clarity of published research while maintaining each author's intent and voice.

"My mission is to help authors turn novel findings into final articles that are rigorous, replicable, and well connected to past literature and future directions."

He also noted that he plans to introduce new peer-review approaches that better support the editorial team, authors, and reviewers.

Editorial priorities outlined for submitted manuscripts include:

Clear structure grounded in the scientific method
Technical soundness with sufficient detail to support replication
Strong linking of prior research to forward-looking ideas while preserving the original voice of authors

Further details are expected in the coming weeks. For information about the journal, scope, and access, visit the Journal of Ecohydraulics website.

IAHR ISE-SED 2026 — Extended abstract submission now open!

Wed, 10 Sep 2025 00:00:00 GMT

The International Symposium on Ecohydraulics (ISE 2026), to be held at EPFL in Lausanne, Switzerland, has opened the call for extended abstract submission with a deadline set for October 31st 2025.

All key information is available on the conference website https://ise2026.epfl.ch/abstract-submission/ together with the abstract template and instructions for the submission.

Please do not hesitate to contact us for further info and clarification. Looking forward to receiving your contribution!

Kind regards,

ISE 2026 Local Organizing Committee
Paolo Perona (chair), Giovanni De Cesare, Azin Amini, Giulio Calvani, Sara Bonetti, Hannes Peter, Luis da Silva, David Vetsch

ISE-SED 2026
International Symposium on Ecohydraulics — Swiss Ecohydraulics Day 2026
16–21 August 2026, Lausanne, Switzerland
https://ise2026.epfl.ch/

X-Posting: International Fish Passage Conference 2026, UC Davis, CA, USA

Mon, 02 Jun 2025 00:00:00 GMT

International Fish Passage Conference 2026

Hosted by the University of California, Davis, at the Campus Conference Center — May 4–8, 2026.

The organizing committee is thrilled to share their progress. They are currently seeking sponsors; if you are interested in learning more, please visit the Sponsorship Information and Registration page.

For more general information, see the Fish Passage 2026 website, or contact the organizing committee by email at InfoFishPassage2026@ucdavis.edu.

Conference deadlines

Sep 1, 2025 — Session and Workshop Proposal Deadline
Oct 15, 2025 — Notification of Session and Workshop Proposal Acceptance
Nov 17, 2025 — Registration Opens
Dec 1, 2025 — Talk and Poster Abstracts Deadline
Jan 15, 2026 — Distinguished Project Award Nomination Deadline
Feb 1, 2026 — Notification of Talk and Poster Acceptance
Feb 15, 2026 — Regular Registration Deadline

The organizing committee is looking forward to welcoming you to UC Davis!

Weighted Usable Habitat Area in the Past and Today

Wed, 05 Mar 2025 00:00:00 GMT

This blog post is going to be a bit less waggish than my previous one on slugs, but I hope you will still find it an interesting read.

Weighted Usable habitat Area (WUA) was introduced in Bovee (1986) and further elaborated in Stalnaker et al. (1995) to assess the availability and quality of aquatic habitats. The calculation of WUA requires one-dimensional (1d), cross section-averaged information on hydraulics (flow velocity and water depth) and a representative grain size. Early WUA approaches therefore relied on simplified 1d assessments. However, many of these simplifications, especially the 1d modeling assumptions, are not so relevant today because two-dimensional (2d) simulations have become more affordable to run, at least for purely hydrodynamics.

To translate WUA assessments into 2d space, some researchers have proposed an intriguingly straightforward method that applies habitat suitability curves to 2d numerical simulation output, then multiplies the combined habitat suitability index of each pixel by the pixel area (see for example, Tuhtan et al. (2012) or Yao et al. (2018)). This approach has been criticized for treating suitability indices as though they were probabilities used to calculate the statistical mean of a dataset, even though they are not probabilities, and it can also lead to confusion because of an ambiguous calculation of WUA.

To better understand this ambiguity, let's take a moment to walk through a simplified version of how WUA is calculated:

Start by defining habitat suitability curves that link suitability indices to water depth, flow velocity, substrate type, and potentially other variables. Each curve assigns a suitability index (SI) ranging from 0 (unsuitable) to 1 (highly suitable) for each variable.
Next, use a 1d hydraulic model to produce depth and velocity data for representative cross-sections in a river segment. The 1d model calculates cross section-averaged flow velocity and water surface elevation along the river centerline.
Based on the 1d-hydraulic model results, compute the habitat suitability index SI for each variable (depth, velocity, substrate, etc.) at every cross-section. For instance, SIh for depth, SIu for velocity, and SId for substrate (where d refers to the diameter of a substrate grain).
Combine the individual suitability indices by multiplying them to obtain the total suitability index at each location: SItotal = SIdepth · SIvelocity · SIsubstrate.
Multiply SItotal by the wetted width of each cross-section to find the Weighted Usable Width: WUW = SItotal · width.
Finally, add up the products of WUW and the representative lengths Δx of considered river reaches across all cross-sections to determine the Weighted Usable habitat Area: WUA = ∑i=1n WUWi · Δx, where n is the number of cross-sections.

2d modeling already modifies Step 2, producing depth-averaged flow velocity and water depth maps that enable the calculation of SItotal for each pixel. This leads to the intriguing expression for computing WUA as a function of the pixel area Apx:

WUA = Apx · ∑ SItotal, pxi,

where pxi refers to each pixel. Although this formulation sounds intuitively straightforward, it diverges from the original WUA concept and can confuse. I personally also find it difficult to interpret: what does the sum of pixel-index products really mean? Consider 10 pixels, where one has SItotal, pxi = 1, and all others are 0 - this yields the same result as having 10 pixels with SItotal, pxi = 0.1. Because 0.1 is nearly unsuitable habitat, it would be surprising to see any fish in that entire area. Yet if there is a single pixel with SItotal, pxi = 1, fish might use exactly that spot to rest and recover, just to prepare for swimming as fast as possible through the "ugly" environment of that pixel.

In seemingly endless discussions with ecologists and stakeholders regarding habitat enhancement for the Yuba River in California, we converged on a solution that feels more correct and easier to interpret than the 2d-WUA expression. Specifically, we set a critical threshold SIcrit, above which SItotal indicates highly suitable habitat for a particular fish species at a given lifestage. Then, we compute the Usable habitat Area, UA, by summing the areas of all pixels whose SItotal values exceed this threshold:

UHA = pxa · ∑ pxi(SItotal, pxi > SIcrit).

SIcrit is often chosen between 0.4 and 0.7, depending on the strictness of the assessment (read more in our paper introducing River Architect / Schwindt et al. (2020)).

As an additional explanation, habitat suitability curves illustrate how environmental factors such as water depth and flow velocity influence the well-being of a specific fish species at a certain lifestage in a particular river. Each curve only applies to the species, lifestage, and river from which its data were originally obtained, so it does not necessarily hold true for different environmental settings or other fish populations because habitat preferences are most likely just "relative preference in that river".

In the meantime, rather than using the product of SI values for each parameter (see Step 4), ecohydraulicists found it more realistic to rely on the geometric mean:

SItotal = (Πpar SIpar)1/n.

For example, combining SIh and SIu through the geometric mean leads to SItotal = (SIh · SIu)1/2.

All of these assessments ultimately refer to snapshots of physical conditions, meaning they are valid only for the specific topography that was simulated. Once a flood alters the morphological structures, the habitat assessment changes. As the calculations consider only physical parameters, there is no guarantee that fish will actually occupy the habitat. Imagine a river with near-perfect suitability indices everywhere, but in reality, the water is too polluted, too warm, or too turbid for fish to spend their lives. They might simply blob away, despite all physically promising indices.

Before the tone of this post becomes too glum: the imperfections in habitat modeling and assessment have already inspired numerous research papers, presentations, and discussions that keep our community vibrant. Seeking a new research project? Open Pandora's box on Ecohydraulics and be prepared for a flood of fresh ideas!

Sources

Bovee, K.D., 1986. Development and evaluation of Habitat Suitability Criteria for use in the instream flow incremental methodology (Biological Report No. 21), Instream flow information paper. National Ecology Center, U.S. Fish and Wildlife Service, Fort Collins, CO, USA.
Schwindt, S., Larrieu, K., Pasternack, G.B., Rabone, G., 2020. River Architect. SoftwareX 11, 100438. https://doi.org/10.1016/j.softx.2020.100438
Stalnaker, C., Lamb, B.L., Henriksen, J., Bovee, K., Bartholow, J., 1995. The Instream Flow Incremental Methodology - A Primer for IFIM, Biological Report. National Biological Service, U.S. Department of the Interior, Washington, D.C., USA.
Tuhtan, J.A., Noack, M., Wieprecht, S., 2012. Estimating stranding risk due to hydropeaking for juvenile European grayling considering river morphology. KSCE Journal of Civil Engineering 16, 197-206. https://doi.org/10.1007/s12205-012-0002-5
Yao, W., Bui, M.D., Rutschmann, P., 2018. Development of eco-hydraulic model for assessing fish habitat and population status in freshwater ecosystems. Ecohydrology 11, 1–17. https://doi.org/10.1002/eco.1961