The Norwegian PRB – Suldal PRB Workshop in Belgirate, 27th-28th Nov 2003 ”Identification of water bodies as potentially heavily modified” by Anja Skiple Ibrekk, Norwegian Water Resources and Energy Directorate (NVE)
The Suldal catchment Typical Norwegian hydropower regulated catchment Many intakes, dams, stream diversions and hydropower plants Some river stretches almost dried out in periods Extensive biological, chemical and hydological monitoring (impacts should be easy to quantify)
Flow reduction due to hydropower regulations in Suldal – run off pattern trough the year
Identification of possible HMWB in Suldal – part of the 1A phase
Meeting in Scottland in November 2003 on HMWB Sweden, Finland, UK, Austria and Norway No countries presented fixed criteria for the identification of water bodies as heavily modified Different criteria will be developed due to wide variations in water body types (and possibly political ambition)
An outline of the identification process Step 1: Delineation Step 2: WB artificial? Yes - HMWB Step 3: Hydro morphological changes? (first screening) Step 4 and 5: Significant changes in hydromorhology so that good ecological status can not be achieved? Step 6: Significant change of character due to human use? Yes on step 2,3,4,5 and 6 - HMWB Step 7: Final identification as HMWB (not done yet)
Criteria developed to identify candidates to HMWB are based on the following issues; Depth of winter drawdown in lakes/reservoirs Reduced low-flow conditions in rivers due to upstream abstractions and changes in retention time in reservoirs Mixing of water from neighbouring rivers (stream diversion) Changes in water temperature affecting ice cover and biota e.g. fish Changes in retention time in lakes affecting chemistry distrubution in the lake e.g. degree of eutrophication
Effects of reservoir drawdown during winter Exposes littoral zone to freezing and ice cover Bottom fauna, macrophytes and fish habitats can be severely affected Most critical for shallow lakes and lakes in cold mountain regions
Stream diversion in Norway Usually in mountainous regions Usually in small streams with steep gradient below the intake Usually with no compensation flow past the intake Usually in steep gradient streams impossible for fish passage Always HMBW below the intake (i.e.dry)
Draft criteria for preliminary HMWB - lakes Lakes regulated more than 10 meters Drawdown of reservoirs: more than 3 m (difference between maximum and minimum water level) Change in the hydraulic load by factor of 5 or more
Draft criteria for preliminary HMWB - rivers Reduction of mean annual flood does not happen more often than every 20th year Change in acidity from above pH 6 to below pH 5.5 Turbidity from < 0.5 FTU to >2.0 FTU Winter temperatures always above +1 deg C Normal annual flow augmented more than 3 times Change in water flow more than 5 % per hour of maximum capacity of the hydropower plant
Drawdown in metres Reservoirs in Norway No of reservoirs registered
Reservoirs with winter drawdown <10 m Clearly HMWB 3 m Intermediate cases Natural 85 181 No. of reservoirs with drawdown exceeding y metres No. unregistered 40 70 (approx.) Total 125 250 of nearly 900 reservoirs in all of Norway
Development of criteria concerning stream diversions Require a simplified approach based on topographical data (hydrology not usually known ) Applied to small stream diversions with no bypass flow, the only issue is ”how far downstream from the intake is it a HMWB?” Low flow assumed proportional to catchment area, and at least 75% of natural low flow required before stream can return to ”natural”
Input to the discussion - HMWB Norway has a wide approach to the identification of HMWB (reason: want the intermediate cases to take part in the full process of identifying HMWB). This categorisation as candidates to HMWB is part of the Art 5 reporting – are similar exercises taken place in other PRBs? How far has the other countries reach in the development of criteria for identification of HMWB? What kind of criteria?