evaluation and minimization of entrainment and impingement a challenge for environmental consultants

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1 0 Marianne Rothensee, Elith Wittrock Sustainable use of cooling water from the Wadden Sea 4. November 2010 Nieuweschans evaluation and minimization of entrainment and impingement a challenge for environmental consultants experiences from the Elbe estuary image source:

2 1 Brokdorf Stade Wedel Moorburg image source:

3 2 Brokdorf Water abstraction between ~ m³/s 3 issues thermal discharge entrainment impingement existing power plants planned power plants Stade Wedel Moorburg image source:

4 3 Evaluation of entrainment and impingement: assessment steps of an environmental consultant 1. assessment of affected species and habitats 2. assessment of existing impacts of E&I 3. prognosis of future impacts of E&I 4. evaluation of future impacts in addition to existing impacts! for Natura 2000 sites cumulative for all planned projects! image source:

5 4 Step 1: assessment of affected species and habitats several protected and also endangered species occur in the Elbe estuary Elbe estuary functions as migration passage, as spawning area and as nursery area for young fish for migrating fish Elbe estuary is only a part of the habitat little information about the fish stocks, especially for protected species which are not of commercial interest insufficient reference information

6 5 Step 2: assessment of existing impacts no studies for entrainment at estuaries in Germany one study about impingement at Brunsbüttel, Brokdorf, Stade (Sprengel 1997) organisms are dominant in the screening debris ( different from rivers) fish are dominant among the screened organisms annual fish loss ranges from 0.5 to 70 t/a annual fish loss extrapolated from fortnightly samples representative? amount of organisms is not consistent with amount of cooling water

7 6 image source: Sprengel (1997):Verluste an Organismen im Bereich der deutschen Künsten von Nordund Ostsee einschließlich der Ästuare durch die Entnahme von Wasser für großtechnischer Kühlsysteme. Brunsbüttel ~ 30 m³/s Step 2: assessment of existing impacts example of impingement of Osmerus eperlanus (Smelt) at two cooling water intakes Brokdorf 60 m³/s several factors influence the fish capture at cooling water intakes the amount of cooling water flow is one of them, but surely not the only one

8 7 Step 3: prognosis of future impacts How many fish will be affected? right river bank fish, esp. swarm fish, are not distributed equally Æ random agglomerations all over the water body probability of being near the water intake depends on water current, tidal effect and particularly on fish behaviour tidal flow shipping channel conclusion for the Elbe estuary: any prognosis would not be reliable image: ARSU intake left river bank

9 8 Step 3: prognosis of future impacts for plankton organisms modelling is possible Particle transportation model to analyse drifting of Twaite shad eggs (Alosa fallax) distribution of particles at low-water slack 5 days after spawning event assumed spawning spot Image Source: modified after DHI WASY GMBH (2009): Partikeltransportberechnungen zur Analyse der Verdriftung von Finteneiern in der Elbe. Im Auftrag der Südwestdeutsche Stromhandels GmbH, Syke, Juni 2009.

10 9 Step 4: evaluation of future impacts? image source: insufficient reference information no reliable impact prognosis fish protection must be as good as possible and ensure, that only minimal fish losses occur US EPA approach: fish protection system must be commensurate with closed-cycle cooling

11 10 Strategies for a fish protection system strategy 2: prevention of entrainment and impingement at trash rakes return system is necessary between water intake and pumps (2) strategy 1: prevention of entrainment and impingement at the cooling water intake between water intake and water body (1) 2 1 discharge intake pumps trash bars travelling screen

12 11 Strategies for a fish protection system strategy 2: reduction of approach velocity fish friendly mechanical barriers (screens with fish buckets) fish return system suboptimal strategy 1: positioning and design of the cooling water intake reduction of intake velocity behavioural barriers electrical deterrent acoustic deterrent light deterrent fish bypass fish friendly mechanical barriers Fine mesh screens at the intake? site-specific and individual solutions! pumps trash bars 2 discharge 1 intake travelling screen

13 12 Challenges on the way to a fish protection system evaluation of the efficiency of the protection system lack of experience in Germany experiences from other countries are often from different water bodies and for different species transferable? for example electrical barriers traditionally applied in Germany scientific studies with contradictory results efficiency depending on location, current, species but influencing factors are often not identified

14 13 Challenges on the way to a fish protection system interaction of technology and biology technical solutions that seem obvious do not always correspond with fish behaviour for example fish return systems: power plant in Mannheim (Germany): discussion whether fish voluntarily enter the buckets proposed solution: stunning of fish with electrical impulse in front of the travelling screen

15 14 Challenges on the way to a fish protection system standards run the risk of unquestioned application for example standard from US EPA: intake velocity of 0.15 m/s how exactly is the standard defined? defined as through-screen velocity refers to a 9.5 mm mesh screen (standard in the USA) includes a safety factor in case screens become partly blocked by debris ensures the prevention of impingement for most species at their different life stages Do these definitions apply to my project?

16 15 Developing a fish protection system an interdisciplinary process Expert knowledge from several disciplines needed: engineers fish biologists producer (of fish protection components) modeller authorities Demand: fish protection system must ensure, that only minimal fish losses occur Experience so far: Reduction of impingement to a minimal level is possible No sufficient measures to reduce entrainment of small organisms

17 16 Outlook Example from Hamburg: Environmental authority restricted cooling water abstraction in a cooling water management plan because of entrainment of small organisms and oxygen deficiency issues Allowed cooling water abstraction is dependent from river flow (max. abstraction 1/3 of river flow). Caused the energy company to build a hybrid cooling tower which will operate during times of low river flow. In some cases the concept of once-through cooling has to be reconsidered, even if sufficient surface water is available.

18 17 Photo: ARSU Thank you for your attention