1 Storages and Environmental Flows Sharad K Jain National Institute of Hydrology, Roorkee

Dams and their Impacts o There were > 47k large, 800k small dams by o Dams serve for multiple purposes: M&I water supply, irrigation, Flood Control, recreation, navigation, … o Dams have helped in meeting increasing water demands by river regulation. o Hydropower dams generate about 20% of world’s electricity. o Dams/Diversions help in ≈20% of world food production. o Dams have large impact on ecological health of rivers and ecosystem services. o Influence of dams extends for 100s of km d/s. o Changes include water temp., sediment tpt, chemistry, floodplains, d/s deltas.

Dams and their Impacts o Among changes, alteration of natural flow regimes harms most river ecosystems and species. o Dams can heavily modify volume of flow d/s, changing timing, frequency, duration of high/low flows, and alter rates of change of flows. o Four primary ecological impacts associated with flow alteration (Richter and Thomas, 2007): 1. It can lead to severely modified channel and floodplain habitats by modifying physical habitats such as riffles and bars in rivers/floodplains, and their biotic composition; 2. Aquatic species have evolved in direct response to natural flow regimes which can be disturbed by flow alteration; 3. Many species are depend upon lateral and longitudinal hydraulic connectivity, which can be broken by flow alteration; and 4. Invasion of exotic and introduced species in rivers can be facilitated by flow alteration.

Dams and their Impacts Purpose of DamImpact on d/s Flows Hydropower – RORMinor alterations in flow regime Additional flashiness due to peaking Hydropower – StorageSignificant alterations in flow regime: timings, rate of change Irrigation – DiversionsReduced volume, variability may be maintained Water supply – StorageSignificant alterations in flow regime, Peak flows substantially reduced, Reduced volumes downstream of dams Flood controlPeak flows substantially reduced, Not much change in volumes Multipurpose – storageSignificant alterations in flow regime, Changes dependent on purposes serving. Silt and nutrient deposition in reservoir, erosion d/s.

Dams - Adaption of Operation o Assess hydrologic changes associated with dam operations. o Determine ecological consequences of identified changes – involve experts and stakeholders. o Other social issues including subsistence or economic uses of river and floodplain, flood control, recreational and tourism values, and cultural or spiritual issues should be incorporated in dam adaptation. o Important to educate + engage stakeholders in an open dialogue about range of pertinent ecosystem services. o Trade-off analysis between pre-dam ecological and social benefits, what can be restored and benefits/costs. o When irrigation or power generation subsidies are large and benefits of Eflows are appreciable, adaptation may be attractive from point of net social benefits. o In case of flood control dams, costs and benefits of changing land uses in floodplain to accommodate modest flood events should be considered.

Options tried in Other Countries o By restoring floodplain storage capacity, projects designed to control a 20-yr flood might be operated to control 50-yr and higher flood events. o Capacity of sluices and spillway to release Eflows can be limiting in many dams; structural modifications to allows higher releases are expensive and not always possible. o Land use in floodplains may be amenable to changes -- adaptation to improve ecological functions of d/s floodplain may be feasible. o Re-establishing a floodplain inundation regime can make floodplain and river more productive for a variety of user groups. o Enhancement of fish and wildlife populations can improve food availability; and many groups use biomass/fiber from floodplains for building material and other purposes. o It can also benefit agriculture on floodplains by regularly depositing nutrients, flushing soil salinity, and recharging aquifers.

Options tried in Other Countries o Floodwaters can be allowed to fill natural depressions on floodplain during high flow. Control temporary flooding by floodgates in levees. o Flood easements: agreements with landowners for use of private lands for flood control for limited time. o Delay in planting crops during inundation, which may be offset to some degree by increased moisture and fertility of soil. o Move levees farther from river – benefits of flood control and ecosystem restoration, partial or full restoration of fluvial processes such as river meandering that benefit aquatic species & vegetation.

Options tried in Other Countries o Hydropower generation: construct a “re-regulating” dam, d/s of project. Capacity of regulating dams is usually small. Hydrologic forecasting o By using a decision support system that includes hydrologic simulation and reservoir operations modeling, with hydrologic forecasts as inputs, a hydropower operator’s ability to meet both energy demands and Eflow objectives can be increased greatly. o Furthermore, hydrologic forecasts can often be improved substantially by installing additional climate and water monitoring instruments in the catchment.

Options tried in Other Countries o Gaining “more crop per drop” o Agriculture is single largest consumptive user of water, strategies for increasing water use efficiency can give water for Eflow restoration in highly allocated rivers. o Water movement in agriculture: (1) water moves upwards – ET; (2) water flows downward, may replenish GW (used later) or percolate into deep aquifers and lost; (3) water flows into biomass – good use; (4) water flows to rivers. o ET can be reduced by improved methods of applying water; infiltration can be reduced by applying proper amounts of water; water flow into biomass can be reduced by planting crops needing less water. Conjunctive use of water o Coordinated operation of dams and aquifers. o In high flow period, store SW and recharge aquifers. o In low flows and where water tables are high, use GW. o With elevated GW levels, more base-flow. o Ganga Water machine.

ASSESSMENT OF E-FLOWS FOR UPPER GANGA BASIN G&D Sites Depth (m) Velocity (m/s) Discharge (cumecs) DVQ Alaknanda (Joshimath) Alaknanda (Rudraprayag) Bhagirathi (Uttarkashi) Bhagirathi (Tehri) Ganga (Devprayag) Ganga (Rishikesh) Min flow requirements in lean period (Nov-May) Min flow requirements in spawning period (June-Oct) Depth (m) Velocity (m/s) Discharge (cumecs) DVQ Alaknanda Rudraprayag = 9600 MCM, Monsoon 7300 MCM Distributed storage of 1500 MCM) in Alaknanda valley can provide 100 cumec for 6 months 10

Environmental Flows and Energy  Uttarakhand: Hydropower potential = 20,000 MW  Harnessed = 3200 MW  Abandoned = 1500 MW  Under review = 1800 MW 21

Epilogue o Integrating Eflow considerations in new dam designs is less expensive, with less social and economic disruption. o In attempts to restore natural flow and sediment transport regimes, consider if it justifies social and economic costs. o Floodplain encroachment by roads, houses, and other structures may limit feasibility of controlled reintroduction of floods.

Epilogue o Benefits from dam re- operation can’t be predicted with a high certainty; changing climate will add new risks. Adaptive management is a must. o In many (arid or semi-arid) river basins, virtually every drop of water has been allocated, leaving little water for river ecosystems. o Economic and cultural dependencies and existing use patterns make it extremely difficult to change allocations. o Current water management goals may be different than those of past generations. How about future ??

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