A consideration of the hydraulic simulation of a dam to reduce algal bloom

1. A consideration of the hydraulic simulation of a dam to reduce algal bloom S.J. Yu, S.R. Ha*, D.I. Jung, J.Y. Hwang, M.H. Chae National Institute of Environmental Research, Korea Chungbuk National University*

2. Background • Climate change frequent draught and flooding • Water demand increase getting higher dam construction dependency • Morphological and climate characteristics in lakes and stream in Korea • The status of water quality in waterworks eutrophication • Hydraulic control in eutrophicated reservoirs will be a key to reduce algal bloom

3. Content Experimental method 1 Daecheong dam reservoir in Korea 2 Algal Bloom Forecasting System 3 Weather condition of the reservoir 4 5 Water quality and algal growth 6 Simulation using CE-QUAL-W2 7 Conclusion

4. Experimental method • Daily inflow, outflow, intake data www.warmis.go.kr • Bathymetry data (KOWACO,2004) • Meteorogical input data : • temp., wind direction, wind speed, cloud, etc. (www.kma.go.kr) • Water quality item at 6 points • temp., Chl-a, COD etc. • ( Guem river water quality lab., NIER) Munyi (T3) Dam(M3) Hoinam(T2) Janggye(T1) Chudong(T2) Chuso(T1)

5. Daecheong dam reservoir in Korea • Artificial dam for multipurpose • Dendritric shaped stream network with 80 km long • The catchment area of the dam reservoirs is covered with mountainous area with a forest • Nutrient load is mainly originated from diffuse pollution sources Morphological and watershed characteristics

6. Water Intake Tower Morphological status and sites Munyi Dam Hoinam Morphological status in Daecheong Reservoir Chudong Wastewater Treatment Plant Chuso

7. Pollutant load in the reservoir Hydrodynamics and water quality in the reservoir are strongly influenced by a local monsoon climate Monthly pollutant loading to Daecheong Dam reservoir, 2002 Non-point source contribution rate in total pollution loading, 2002

8. Algal Bloom Forecasting System • Water quality deterioration and algal toxins in waterworks • Duration : April to November • 10 reservoirs

9. Munyi,(T3) The status of Algal Bloom Forecasting System Hoinam(M2) Chudong (T2) • draughty season • Heavy rainfall • Low duration of sunshine Algal caution level Algal warning level Algal outbreak level Where nutrients come from?

10. Water quality and algae Is chl-a not always correlated with COD ? The relationship between COD & chl-a in the surface water

11. Alagal propagation characteristics Hoinam, M2 Chuso, T1 Munyi, T3 After August, the number of cyanobacteria were dominant Cyanobacteria increase in high temperature

12. * KOWACO (http://warmis.or.kr) Weather condition of the reservoir Monthly circulation rate influence on water current to move nutrient and algae !!

13. Simulation using CE-QUAL-W2 • Reliability of bathymetry file in the reservoir - water level (2001, 2003) • Stratification of the reservoir • The comparison between velocity and algal propagation • Water current, temperature variation by hydraulic simulation(2003) Two scenarios based on augmentation of spill flow To interpret water current, water temperature of the reservoir To consider the hydraulic condition to reduce algal bloom

14. CE-QUAL-W2 Model • CE-QUAL-W2 model is based on the assumption that flow and transport phenomena in lake with a distinct flow direction and a regular bathymetry can be computed from laterally integrated Navier-Strokes equation (Bloss et al., 1998). • Flow and the distribution of heat are governed mainly by a dynamic balance between the advection transport in the longitudinal (and to some extent vertical) direction and the turbulence (diffusive) transport in the vertical direction. • Water Quality • Conservative tracer • SS, Coliform bacteria, TSD • Labile-, Refractory-DOM • Algae • Labile-, Refractory-POM • Phosphorous • NH3, NOX- nitrogen • DO, pH, CBOD • CO2, HCO3, CO3 • Fe etc. (22 items)

15. Dam Str. Sokcheon Main str. Geum river Model application in the reservoir • 6 branches with different direction • 117 segments so as be right against water flow • 26 layers with 2 m interval in depth • Period : 2001, 2003 • Simulated Water Quality : Temp., Water velocity

16. Model parameter

17. Reliability of hydrodynamic model * KOWACO(http://warmis.or.kr) 자료 • Computing the distribution in terms of current discharges, velocities and the change in water surface elevation. • Good agreement : water surface elevation from 63m to 78 m

18. M3 Calibration and verification M2 M1 M1 M2 M3

19. T3 Calibration and verification T2 T1 T1 T2 T3

20. Main stream Boundary The Stratification by temperature 26∼28℃ A important factor to induce algae propagation and cyanobacteria growth

21. Back flow nutrient Finally, back flow in the middle layer toward T2 and T3 resulted in nutrient supply. Water current with density flow Muni,T3 Hoinam Chudong, T2 Chuso

22. Munyi, T3 Hoinam Chudong, T2 Chuso Water current As temperature increased at the surface water, algal caution level occurred

23. Munyi,T3 Hoinam Chudong,T2 Chuso Water current In according to temperature increase, algae continued to propagate in the stagnate zone with shallow depth

24. Scenarios by spill flow augmentation Water level change Outflow change • Through the control of outflows, hydraulic condition during a storming shows dramatic changes not only temporally but also spatially due to an inner hydraulic balance of fluid flows (black dotted line). • Considering outflow augmentation to control nutrient transport and temp. for the management of algal growth • Two scenarios ; spill flow increase so as to maintain water level above 65 m • - 1st : after the early of August • - 2nd: 1st + after the end of August

25. Water current change • Back water current • Simulation results : proceed toward dam site • 2nd simulation results • within proper velocity after heavy rainfall

26. T3 M2 T2 Temperature variation by scenarios it induced in the instability of water body of the stagnate zone so that water temperature declined. temperature drop Period shorten M2 T2 T3

27. Conclusion • This study is aimed to estimate the water current and temperature effect to reduce algal bloom by the simulation of dam spill flow control using water quality model, CE-QUAL-W2 in 2003. • Water current was resulted in nutrient transport from the upstream of main reservoir and nutrients were delivered up to downstream by fast water velocity. • Algal blooms occurred in stagnated zone of main reservoir downstream as the current of downstream was retarded according to dam out control.

28. Conclusion • Consequently, water balance in stagnate zone triggered a rise of water. • The simulation result by outflow control scenarios showed that spill flow augmentation induced in water body instability of stagnate zone so that water temperature declined. • It could be suggested that outflow control minimized algal bloom in the downstream in the flooding season as long as water elevation is maintained properly.

29. A consideration of the hydraulic simulation of a dam to reduce algal bloom Thank you for your attention