Project name: Rehabilitation Program after the August 4, 2023 Floods – Mislinja, Šentjanž pri Dravogradu to Bukovska Vas
Location: Drava River Basin (Mislinja River), Koroška Region, Slovenia
Investor: Ministry of Natural Resources and Spatial Planning of the Republic of Slovenia – Water Directorate, Drava River Basin Sector
Design team: VGP Drava Ptuj is a well-established team of experienced engineers and water management professionals, with nearly 80 years of tradition in delivering comprehensive solutions for river engineering, flood protection, and sustainable water infrastructure.
The goal: To prepare comprehensive project documentation for the rehabilitation of flood-damaged river sections, with the aim of restoring flow capacity, stabilizing riverbanks, and protecting key infrastructure — all while incorporating nature-based solutions to enhance ecological resilience and sustainability.
Design objects: The project covers a 23.2 km highway section (LOT 3,4,5) with complex geomorphological conditions. LOT 5 subsection has length of 7.5km. The scope includes alignment design, optimization of route variants, detailed solutions for landslide mitigation, regulation of watercourses, embankment construction, and integration of all necessary infrastructure elements.
Software solution used: Aquaterra (CGS Labs), HEC-RAS, HEC-HMS
In early August 2023, extreme rainfall events caused catastrophic flooding across northern Slovenia. The Mislinja River, a first-order watercourse in the Drava River basin, experienced extensive damage. High floodwaters eroded large portions of the riverbanks, inundated surrounding properties, and even triggered a landslide on the right bank, posing a direct threat to an existing residential building.
The flood event led to major structural instabilities along several river sections, with scouring and undercutting visible throughout. Bank erosion, sediment deposition, blocked culverts, and hydraulic bottlenecks significantly reduced the river’s flow capacity and increased the risk of future flooding.
The company VGP Drava Ptuj, one of the leading water management companies in Slovenia, took charge of the rehabilitation effort. With nearly 80 years of expertise, the company provides public watercourse maintenance services across the Drava River basin and manages numerous complex commercial and EU-funded projects.
In the Mislinja project, VGP Drava Ptuj focused on sectional rehabilitation of the most critically damaged areas, with the goal of restoring flow capacity, stabilizing the terrain, and protecting infrastructure, all while respecting the river’s natural path and adjacent property boundaries. The solution combined precise terrain modelling, hydraulic analysis, and modern civil design tools, including Aquaterra, to deliver a reliable and sustainable result.
From terrain capture to design – integrated workflow
In the Mislinja project, the primary goal was to restore stream flow capacity, stabilize the eroded riverbanks, and protect nearby road infrastructure within the existing riverbed geometry. To achieve this, the technical team first had to capture the current terrain conditions with high precision.
Using drones equipped with GNSS receivers, VGP Drava Ptuj conducted detailed aerial photogrammetry of the affected area. The generated point cloud data was merged with publicly available LiDAR datasets and supplemented by classical geodetic measurements with total stations and GPS devices. The result was a highly accurate digital terrain model (DTM) which formed the foundation for all subsequent hydraulic and engineering design tasks.
The hydraulic model of the Mislinja was developed to simulate maximum flood water levels. These water surface elevations were then used to determine the extent of inundation and to prepare detailed cross-sections every 25 meters. The data were processed using 3Dsurvey, exported to Civil 3D, and the hydraulic modeling in HEC-RAS as well as the river design were carried out using CGS Labs’ Aquaterra software.
Image: Integrated River Rehabilitation Workflow with Aquaterra.
Designing with Aquaterra – Easy and Efficient from Start to Finish
Throughout the Mislinja River rehabilitation project, Aquaterra proved to be an very important tool in every design phase — from terrain analysis and hydraulic integration to cross-sectional modeling and quantity calculations. The software supported the team in managing a complex, dynamic project with high demands for accuracy, speed, and compliance with both technical and spatial constraints.
The project team used Aquaterra to:
- Import terrain data
- Define the river axis
- Create longitudinal profile
- Generate cross-sections at 25-meter intervals, including of water levels and terrain
- Design structural and nature-based riverbank protections
- Calculate planimetric quantities
- Integrate hydraulic simulation results from HEC-RAS—such as maximum flood levels—directly into the design environment
One of the most praised features of Aquaterra by the VGP Drava Ptuj team was its user-friendly interface and streamlined workflow, which enabled quick progress and minimized repetitive manual tasks. For example, automated drawing of water levels in longitudinal and cross-sectional views, as well as intelligent propagation of design elements (Typical Cross-sections elements), significantly reduced drawing time.
Image: Construction layout.
Another notable advantage was Aquaterra’s interoperability with other tools such as Autodesk Civil 3D, BricsCAD, HEC-RAS, and King Prostor, enabling a fully integrated, BIM-compatible process — even when terrain data or hydraulic results were updated mid-project.
“The main advantage of the Aquaterra software is its connectivity with other programs. Data can be transferred quickly and easily from Aquaterra to MIKE FLOOD or HEC-RAS.”
– Neven Verdnik, Head of Technical Department at VGP DRAVA Ptuj, d.o.o.
Integrating Nature-Based Solutions into River Rehabilitation
An important aspect of the Mislinja River rehabilitation project was the consideration and integration of nature-based solutions (NBS) — a design philosophy that aims to combine hydraulic functionality with ecological benefits and long-term sustainability.
Rather than relying solely on hard, impervious structures like concrete walls, the project team evaluated and incorporated natural and semi-natural protection measures that support riverbank stability while enhancing biodiversity and landscape value.
Some of the nature-based elements considered or implemented include:
- Stone crib walls: Constructed from wooden frameworks filled with natural stone, these structures provide bank support, reduce flow velocity, and create good conditions for vegetation growth.
Image: Typical cross-section and proposed types of riverbank protections.
- Vegetated slopes and bank reinforcements: Where possible, eroded slopes were reshaped and stabilized with topsoil seeding, live vegetation, or biotechnical materials that promote root development and surface binding.
- Soft embankment geometry: Instead of rigid, angular profiles, banks were reshaped into gentler slopes to allow floodwaters to dissipate energy and encourage natural sediment deposition.
- Use of in-situ materials: Locally sourced stone and soil were prioritized for embankment and channel reconstruction, reducing the environmental footprint and blending visually with the surroundings.
- Preservation of riparian vegetation: Existing trees and shrubs along the river corridor were preserved wherever possible to maintain shading, bank cohesion, and habitat continuity.
- Support for habitat formation: In certain areas, flow-retarding features such as large woody debris or low sills were designed to create pools and riffles, improving ecological diversity.
Image: Details of fish shelters designed from stone and wood structures to enhance aquatic habitat diversity within the rehabilitated Mislinja River river.
By combining structural and ecological approaches, the project addressed both immediate flood risks and long-term river health. This aligns with broader EU directives on sustainable water management and climate adaptation.
style=”color: #000000;”Conclusion
The successful preparation of project documentation for the Mislinja River rehabilitation demonstrates how modern design tools like Aquaterra can support technically demanding and environmentally sensitive initiatives. The VGP Drava Ptuj team highlighted not only the software’s powerful features and efficient workflow, but also the excellent technical support provided by CGS Labs — fast, knowledgeable, and solution-oriented.
They strongly recommend Aquaterra to all companies engaged in river engineering, highlighting it as a specialized and time-saving solution that supports efficient design and is highly compatible with other software solutions.
“Aquaterra is a specialized solution that’s ideal for companies involved in river engineering design. It is easy to use, saves time, ensures design accuracy, and is highly compatible with other software solutions.”
– Pavel Janko, project designer, VGP DRAVA Ptuj, d.o.o.
About the Company
VGP DRAVA Ptuj d.o.o. is one of Slovenia’s leading companies in the field of water management and hydraulic engineering. With nearly 80 years of continuous operation, the company has built a strong reputation for expertise in the design, maintenance, and rehabilitation of watercourses, as well as the construction of flood protection infrastructure. It is one of only a few companies in Slovenia with a long-standing concession for public watercourse management, covering the Drava, Meža, and Mislinja river basins, and other tributaries flowing into the Adriatic Sea (excluding the Soča River).
In addition to its public service activities, VGP Drava Ptuj actively participates in commercial and EU-funded projects, providing complex engineering solutions for municipalities, state agencies, and private clients. Its technical department is composed of experienced professionals who specialize in river regulation, hydraulic modelling, and modern infrastructure design — always with a focus on both functionality and environmental responsibility.