The Test Cases of Guma and Vadocondes are situated on the Duero River, which is located in the northwest part of Spain. Duero River source is in Castilla y León region, crossing it from East to West and entering in Portugal where finishes its way in the Atlantic ocean. The total length of the river is about 900 km and the catchment area 98400 km2.  The presence of hydropowers in the Duero River is quite common, having 140 small hydropower plants (below 5 MW) and 23 large HPP.

The hydrology of the Duero River on this zone is characterized by low flows in summer (regulated flow for irrigation mostly derived through channels) and medium-high flows during winter and early spring, associated with rainy season and snow episodes.

Upstream migration period for native cyprinids is from April to June, with mean monthly flow in the Guma-Vadocondes case of study reach, between 15 and 30 m3/s approximately.

Guma and Vadocondes hydropower plant

Boths, Guma and Vadocondes, are run-of river hydropower plants with an installed capacity of 2.25 MW (Guma) and 1 MW (Vadocondes) respectively. Each has 2 Kaplan turbines installed.

Guma and Vadocondes are separated only for 3.9 km, having the Duero River the same flows for both HPP. The mean annual discharge is 17.6 m3/s, varying between 6 and 48.9 m3/s as a minimum and maximum mean annual discharge.

The Case Study site and relevant water body of the Duero reaches from 28 km upstream of the Guma HPP to 16 km downstream of the Vadocondes HPP. HPPs are placed in Guma and Vadocondes villages (Duero River, Burgos province, Central-North of Spain). Distance between both HPPs is about 3.9 km –close to the end of the Vadocondes reservoir is Guma dam– and they are operated coordinately (flow and time) by the same company (SAVASA). Vadocondes reservoir has a length of about 2 km and Guma 3 km (the influence of slow waters), with a maximum depth in Guma of about 8 meters and in Vadocondes of 2.5 meters. The bypass reach in both cases is of about 150 m, having upstream devices, specifically pool and weir fishway in Guma and vertical slot fishway in Vadocondes

Layout of HPP Vadocondes

Layout and surrounding area of the HPP Vadocondes

Layout of the HPP Guma

Layout of the HPP Guma

Country Spain
River Duero
Operator SAVASA
Capacity Guma: 2.25 MW,
Vadocondes: 1 MW
Head Guma: 8.85 m,
Vadocondes: 3.75 m
Inter-annual discharge 17.6 m³/s
2 Kaplan turbines at each HPP

The Operator: Savasa
SAVASA (Salto de Vadocondes S.A.) is a small hydropower company which operates the HPPs of Guma and Vadocondes. It has always shown an interest for fish conservation, being a pioneer on this region implementing devices for fish movement and the improvement of the knowledge about fish behaviour building, for example, a scientific fish swimming flume on its installations.

Challenges at the Test Case

Pressures on the water body's ecosystem
Several dams with different purposes upstream and downstream of the two HPPs pose a problem for the continuity of the water body and thereby for fish migration. The native fish species are in decline and several alien species are appearing and/or increasing in number. The flow is highly regulated for irrigation and hydropower uses and there are a lot of artificial lentil habitats due to the presence of dams, which has an effect on the hydrology. There is a heavy agricultural use in the area with a significant use of agrotoxins, which leak into the water. Several dams block the sediment transport, especially since there is no law that enforces an improvement of the situation.

Fish population
The river is dominated by small and medium size reophilic native cyprinids like Iberian barbel (Luciobarbus bocagei), northern straight-mouth nase (Pseudochondrostoma duriense), Northern Iberian chub (Squalius carolitertii) and Pyrenean gudgeon (Gobio lozanoi). All of them are suffering a decrease in their populations (specially nase, which is an endemic species) and alien species are increasing their presence (mainly Alburnus alburnus).

Upstream migration
The main facilities for upstream migration are the fishways built on each dam (all native species are potamodromous). At Guma, it is a pool and weir fishway, with submerged notch with bottom orifice. It has a slope of 8.77 % and covers a trial height of 8.85 m. Vadocondes has a vertical slot fish pass with a trial height of 3.75 m. Both have supplementary attraction flow into the fishway entrance.

Due to the hydropower plant type (over the dam and run-of-river type), there is no legal requirement for ecological flow. Nonetheless, fishways always must have enough flow for operating and therefore the downstream by-pass of the river always maintains a minimum flow of 0.25-0.50 m3/s.

Continuity significant
Hydrology moderate
Morphology moderate
Agriculture high
Pollution minimal
Fish population high
Fish migration
Iberian barbel, northern straight-mouth nase, Northern Iberian chub
Vadocondes dam: vertical slot fishway
Guma dam: pool and weir fishway
Research objectives and tasks

This hydropower plant type (run of river) is quite common on the main Spanish river basins. The work at the Test Case site aims at improving the knowledge on the impacts this type of HPP has on fish migration and location of ascent paths. Different flow configurations through the turbines and fishway-attraction flow will be tested to maximize the relationship between fish upstream movement and hydropower production. Also, fish passage through turbines and their survival using different turbine configurations will be an important result about HPP management and impact.

Research tasks
The research tasks and field studies conducted at the Guma and Vadocondes HPPs are:

  • Population and habitat analysis
  • Analysis of the conceptual solutions and facilities for fish migration
  • Assessment and improvement of fish mortality in the turbines
  • Spawning areas and hydro-morphology to attain self-sustainable populations
  • Migration facilities and attraction flow
  • Hydraulic modelling of attraction flow


Main FIThydro partners involved in the research at the Guma and Vadocondes HPP

Research topics FIThydro partners
Upstream and downstream migration Itagra.ct, SAVASA
Fishway and flow attraction Itagra.ct, SAVASA, IST-ID
Turbine passage and fish survival Itagra.ct, SAVASA, VOITH, TUT, TUM
Research objectives
Upstream & downstream migration
Attraction flow
Fishway attraction
Turbine passage and fish survival
Update and results

Results show that the most abundant native species in the river reach affected by the HPPs are Luciobarbus bocagei and Gobio lozanoi. A few years ago, Pseudochondrostoma duriense was also present in the reach, but it has suffered an important decline in recent years (information obtained from collected data and observations from river authorities, fishermen and people from nearby villages). Current fish assemblage is mainly characterized by the presence of invasive and alien species, probably due to the dominance of lentic sections. Alburnus alburnus, an invasive fish species in the Iberian Peninsula, is the most abundant, even relatively to native ones. In addition, alien crayfishes (Procambarus clarkii and Pacifastacus lenisculus) keep an important presence in the river reach.

The potential spawning grounds for native cyprinids are scarce in the studied reach (six in total), representing less than 2% of the riverbed area. The low availability of spawning grounds seems to be influenced by the floodable areas of both HPP reservoirs. Moreover, the spawning areas show excessive silting.

Regarding Guma and Vadocondes fishways efficiency, 52% (211/411) and 31% (27/87) of the tagged fish (L. bocagei and P. duriense), respectively, were detected during their upstream movement. The ascent success for Guma was 61% (129/211) and 70% (19/27) for Vadocondes. Median ascent time was less than 4 h, with a median time per meter of ascended height of 26 min/m in Guma and 6 min/m in Vadocondes. These values seem to indicate that both structures do not cause an important migration delay for the tagged fish species. Recorded fish movements were related to water temperature and peak flows (Fig. 1) .

In addition, the collected data reveals that Guma fishway can be a downstream migration route, as well. Regarding the fish that were released upstream Guma dam, 42% (144/343) were found in the fishway and 64% (92/144) of these fish completed the descent.

Tagging of fish for fish tracking

Tagging of fish for fish tracking

PIT antenna installation for fish tracking

PIT antenna installation for fish tracking

Electrofishing in the fishway at HPP Vadocondes

Electrofishing in the fishway at HPP Vadocondes

Fish tagging with Visible Implant Elastomer

Placing of deadwood for habitat creation

PIT antenna installation in the fish pass at Vadocondes HPP

PIT antenna installation in the fish pass at Vadocondes HPP

picture rights: © GEA, Ecohidráulica