Introducing the WBG Guidelines for selecting EFlow assessment methods Cate Brown
This presentation Factors affected potential impacts Level of detail in EFlows assessments: Magnitude and complexity of potential impacts WBG safeguard requirements Guide to selecting EFlow assessment level Examples
FACTORS AFFECTING IMPACTS
EFlows and hydropower HPPs can change rivers in four main ways of relevance for EFlow Assessments: Partial or whole dewatering of a reach Changes in pattern of flows of water and sediment Lost of connectivity: Longitudinal - barrier effect of the dam wall and the reservoir Lateral reduced flooding of floodplains Diversions to another basin, which affects two river
Factors influencing potential impact Location Design Operation Effectiveness of barrier to longitudinal connectivity lost along the river Combining two or more of the factors will usually increase the impact.
Location Water flow Sediment flow Connectivity
Location Lower operational constraints Smaller changes to: Water flow Sediment flow Connectivity
Design Water flow Sediment flow Connectivity
Design Flowing water No change to water flow Minor change to sediment flow Barrier effect relatively easily overcome
Design Barrier effects extremely difficult to overcome Still water Potentially major changes to pattern and volume of water and sediment
Design Potentially dewatered river reach
Operation Water flow Sediment flow Connectivity
Operation Sediment flushing may be effective to tackle the loss of reservoir storage as a result of siltation can have serious impacts on downstream ecosystem blankets habitats reduces oxygen fish kills can be mitigated by: controlling sediment conc. timing sediment releases Water flow Sediment flow Connectivity
Run-of-river hydropower Used to describe a considerable range of designs: HPPs with no storage, (i.e. inflow matches outflow minute by minute) HPPs with limited storage and no peaking-power releases (e.g. inflow matches outflow over c. 24 hours) HPPs with moderate storage and peaking-power releases HPPs that rely on large upstream storage facilities HPPs where the flow of a river is diverted from the host river to another river Of limited value from an EFlows perspective In the guidelines: True run-of-river HPPs Hydropower plants that release downstream into the same river, with a short or no diversion, have 48-hour dry-season storage and do not make peaking-power releases
LEVEL OF DETAIL IN EFLOWS ASSESSMENTS
DISCHARGE EFlows assessment methods/levels Over 300 methods Simple ones from 1970s to more modern holistic methods Three levels of detail: Low resolution Medium resolution High resolution (a) Banktop JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC (b) Water levels corresponding to break points Wetted perimeter Tennant Method CHANNEL AND HABITAT MAINTENANCE FLOODS (second building blocks) LOW FLOWS (first building blocks) MONTHS Discharge Banktop Break points in slope SPAWNING/ MIGRATION FRESHES (third building blocks) DRIFT
Usually desktop Low resolution Hydrological or hydraulic data are analyzed to derive standard indices as recommended flows Typically prescriptive Result in a recommended flow based on data extrapolated from areas where more detailed studies have been undertaken No detail on the responses of habitat or species
Medium and high resolution Medium- and high-resolution methods are similar: Many are interactive through the use of scenarios Collect and use data from the study river Many focus on establishing a relationships between changes in river flow and one or more aspects of the river. Many methods can be used at medium or high resolution They are distinguished from one another by: spatial scope number of components level of effort in collecting and analysing local information High-resolution usually incorporate issues such as: survival of individual species impacts of sediment reduction effects of peaking-power releases other river- or project-specific variables, such as management interventions.
Other important differences between method Prescriptive recommend a flow Interactive provide implications of different flows Prescriptive no information on what will happen if you don t meet EFlows requirements Interactive information of allow tradeoffs
Relative cost of assessment Level of resolution Units Low- Resolution Medium- Resolution High- Resolution Team and effort No. of people People 1-2 3-6 3-10 No. of site visits Trips 1 1-2 2-3 Duration Months 1-2 6-12 6-24 Time estimates Total Person days 5-12 40-140 130-290 Cost (excl. disbursements) US$ (x1000) 4 10 32 112 100 232
Relative cost of assessment Using conservative total cost US450 million: Low = 0.001 0.002% Medium = 0.007 0.024% High = 0.22 0.52%
Link between potential impacts and EFlows assessment level As potential impacts increase in magnitude and complexity: Need to greater understanding of implications and options Need for greater detail in assessments For instance if potential impacts include: Timing of seasons Large within day flow changes Flooding of floodplains Sediment supply Barrier to upstream and downstream movement Does not make sense to set 10% minimum flow without further investigation
Link between WBG safeguards and EFlows assessment level OP 4.04 Natural Habitats OP 4.36 Forests OP 4.10 Indigenous People OP 4.11 Physical Cultural Resources ESS6/PS6: Biodiversity Conservation and Sustainable Management of Living Natural Resources ESS7/PS7: Indigenous People ESS8/PS8: Cultural Heritage Biodiversity Ecosystem services River connectivity Nutrient cycling Natural Resources Livelihoods Spiritual and Cultural Resources Cultural Heritage Resources Cultural Practices and Ceremonies OP 7.50: International Waterways All of above
Other factors affecting EFlow assessment level Other developments Position in a cascade Type of ecosystem affected High level of social dependency
GUIDE TO SELECTING EFLOW ASSESSMENT LEVEL
Tools to guide selection of EFlow assessment level Decision-tree EFlows Screening Tool In general, these will recommend: Low-resolution methods for HPPs that will not affect natural and critical habitats; for true run-of-river projects; or for baseload plants that have no substantial influence on the flow regime. Medium-resolution methods for HPPs that that will not affect critical habitats; low social dependence; or are near other existing HPPs (e.g., cascade of dams) as long as they are not the most downstream one. High-resolution holistic methods for HPPs that will affect critical habitats; OR ecosystems other than rivers; OR high social dependence OR transboundary or has a trans-basin diversions.
The decision tree
True 'RoR' Dewatered reach between dam wall and tailrace? Limited to medium storage Large storage Peaking? No Yes Assessment of the d/s impact of peaking T r a n s b o u n d a r y b a s I n? Yes No Trans-basin diversion? No Ecosystems other than river affected, e.g., wetlands, estuary? No High level of social dependency / use? No First or most d/s in a cascade? Yes Yes Yes Yes No Protected Area or Critical Habitat? No Yes Yes Modified Habitat? No LOW-RESOLUTION MEDIUM-RESOLUTION HIGH-RESOLUTION
EXAMPLES
Poonch River Mahaseer National Park Golden Mahaseer
Gulpur HPP retrospective
EFlows assessment: Scope and costs (2014/15) Four sites, one upstream, one between the dam wall and the tailrace and two in the river downstream of the tailrace and Mangla Dam. The EFlows scenarios incorporated considerations of: changes to pattern and volume of downstream flows the downstream effects of sediment trapping and/or flushing changes in connectivity assessment for key migratory fish options for turbine selection options for management protection (i.e., offsets). The team = 4 international consultants with EFlows experience, who guided a team of Pakistan specialists through the assessment. Cost to client: ± US$ 300 000.00 inclusive of disbursements.
Poonch River Batoka Mahaseer Gorge National Park HPP
Batoka HPP retrospective
Two sites downstream of the tailrace to Kariba Dam. The EFlows scenarios incorporated considerations of: changes to pattern and volume of downstream flows the downstream effects of sediment trapping and/or flushing changes in connectivity assessment for key migratory fish (Victoria Falls) The team = 6 consultants: EF specialist Hydraulics Geomorphology Vegetation Inverts Fish EFlows assessment: Scope and costs (2014) Cost to client: ± US$ 110 000.00 inclusive of disbursements.
Proposed design for Bute Inlet array (individual)
Summary Guide to promote a standard approach to EFlows Assessments in WBG-funded HPPs: based on the context in which EFlow to be assessed and applied; allows for selection of project-appropriate EFlows Assessment methods, and; Stronger links with ESIAs, CIAs and SEAs
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