Location: Nalón, Narcea and Navia Rivers
Dates: 2018 – 2025
Area: Environmental Engineering Area
In river management, reliable data are those that allow decisions to be made without doubts: checking whether the ecological flow is being complied with and translating levels into real flows with reliable flow curves.
From TAXUS MEDIO AMBIENTE we have developed campaigns in the rivers Nalón, Narcea and Navia, with a double objective: to obtain punctual measurements that verify the ecological flow near the chosen points; and to refine flow curves measuring in different conditions (from low water to high flow episodes).
Although this case has been developed in the Nalón, Narcea and Navia rivers (Asturias), the methodology is fully replicable in basins throughout Spain, adjusting the design of the campaign and the quality controls to the local hydrology and the criteria of each River Basin District. This is the basis of the work we have done, selecting the most appropriate technology for the conditions of each section and depending on the flow scenario.
The key: choosing the right tool
In shallow and homogeneous sections we opt for the inductive magnetic sensor, which measures by verticals. It is the indicated option when the draft is less than 30 cm and the channel is homogeneous; it allows us to obtain a precise point value, especially when the ADCP is not feasible due to lack of draft. The trade-off is time: each point requires more dedication to ensure robust data.
When the stretch and the regime allow it, we deploy a five-beam ADCP (acoustic Doppler profiler) on trimaran, operating in both slow and fast waters and capable of measuring up to 25 m depth. The equipment travels the riverbed from bank to bank and generates a data grid with information on speed, direction and depth in 5×5 cm cells. To consider the gauging valid we applied quality criteria: 4 pairs of transects, a total duration > 720s and a discrepancy < 4% between valid transects.
How we articulate it and what it brings
The job is not just to go and measure. We design campaigns in different flow scenarios, prioritizing the proximity to the release point and applying data quality criteria (repeatability, discrepancy control and minimum times), so that the punctual measurement has continuity in a useful flow curve for daily operation.
On the one hand, it provides documented verification of compliance with the ecological flow in different scenarios, with measurable and comparable evidence over time. On the other hand, it provides more accurate flow curves, constructed from real gauges, which allow fine-tuning the release in dams and weirs and responding with solvency to inspection requirements.
These campaigns have been carried out since 2018 with inductive magnetic sensor and since 2022 with ADCP. Technicians from the Cantabrian Hydrographic Confederation have participated in certain gauging. The service has been provided for clients such as TRAGSATEC, EDP, ENCE and REPSOL.