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1.2 flood damage mitigation reservoirs


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Flood Damage Mitigation Reservoir

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1.2 flood damage mitigation reservoirs

  1. 1. Flood Damage Mitigation Reservoirs
  3. 3. Types of Reservoirs a. Storage/Conservation Reservoir b. Multi-purpose Reservoir c. Distribution Reservoir d. Flood Control/Mitigation Reservoir
  4. 4. Storage/Conservation Reservoir A storage/conservation reservoir can retain such excess supplies during periods of peak flows and can release them gradually during low flows as and when the need arises.
  5. 5. Multi-purpose Reservoir A multi-purpose reservoir is planned and constructed to serve not only one purpose but various purpose together. Managed to balance: - Water supply - Navigation - Flood control - Recreation - Soil Erosion - Irrigation - Environmental management - Hydroelectric power generation
  6. 6. Distribution Reservoir A distribution reservoir connected with the conduits of a primary water supply; used to supply water to consumers according to fluctuations in demand over short time periods and serves for local storage in case of emergency.
  7. 7. Flood Control/Mitigation Reservoir A flood control reservoir stores a portions of the flood flows in such a way as to minimize the flood peaks at the areas to be protected downstream.
  8. 8. Types of Flood Mitigation Reservoirs a. Storage Reservoir b. Retarding Basins
  9. 9. Storage Reservoir The discharge from a storage reservoir is regulated by gates and valves operated on the basis of the judgment of the project engineer. It differs from conservation reservoirs as they need large sluiceway capacity in order to allow rapid drawdown before and after a flood.
  10. 10. Retarding Basin A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of rivers, streams, lakes or bays to protect against flooding and, in some cases, downstream erosion by storing water for a limited period of time.
  11. 11. Next… Purpose of Flood Mitigation Reservoirs
  12. 12. References • 5e/ac675e04.htm • Slideshare • Google • Wikipedia
  13. 13. Prepared by: Ivy Diane L. Ramos Purpose of flood-mitigation reservoirs and locations of reservoirs
  14. 14.  In environmental engineering, flood mitigation involves the management and control of flood water movement, such as redirecting flood run-off through the use of floodwalls and flood gates, rather than trying to prevent floods altogether. It also involves the management of people, through measures such as evacuation and dry/wet proofing properties. Purpose of Flood-mitigation reservoir
  15. 15.  This is accomplished by discharging all reservoir inflow until the outflow reaches the safe capacity of the channel downstream. All flow above this rate is stored until inflow drops below the safe channel capacity, and the stored water is released to recover storage capacity for the next flood  The reservoir must be operated so as to produce a minimum water level at the protected area, rather than a minimum at the dam
  16. 16. The prevention and mitigation of flooding can be studied on three levels: individual properties small communities whole towns or cities.
  17. 17.  Property owners may fit their home to stop water entering by blocking doors and air vents, waterproofing important areas and sandbagging the edges of the building. Protection of individual properties
  18. 18.  When more homes, shops and infrastructure are threatened by the effects of flooding, then the benefits of greater protection is worth the additional cost. Temporary flood defenses can be constructed relatively quickly in certain locations and provide protection from rising flood waters. Rivers running through large urban developments are often controlled and channeled. Water rising above a canal's full capacity may cause flooding to spread to other waterways and areas of the community, which causes damage. Defenses (both long-term and short-term) can be constructed to minimize damage, which involves raising the edge of the water with levees, embankments or walls. The high population and value of infrastructure at risk often justifies the high cost of mitigation in larger urban areas.  Protection of communities
  19. 19.  The most effective way of reducing the risk to people and property is through the production of flood risk maps. Most countries have produced maps which show areas prone to flooding based on flood data. Flood risk management
  20. 20. Location of Reservoir
  21. 21.  Rim stability  Water-holding capability  Loss of reservoir water  Seismicity  Sedimentation  Bank storage  Topography  Geology  Local condition Factors Affecting Location of Reservoirs
  22. 22.  Topography a narrow site will minimize the amount of material in the dam thus reducing its cost, but such site may adaptable
  23. 23.  Geology the foundation of the dam should be relatively free of major faults and shears. If these are present they require expensive foundation treatment.
  24. 24.  Local Condition site availability of water supply, sewerage disposal, electric power for construction purposes, telephone service should be chosen.
  25. 25.  Rim stability and water-holding capability are interrelated. Rim failure can be caused due to either the sliding or the erosion of a segment of the reservoir rim. Seepage of water is mainly responsible for such failures.
  26. 26.  Loss of reservoir water to the atmosphere occurs due to direct evaporation from the reservoir surface. The evaporation losses are affected by the climate of the region, shape of the reservoir, wind conditions, humidity, and temperature. From considerations of evaporation, a reservoir site having a small surface area to volume ratio will be better than a saucer-shaped reservoir of equal capacity.
  27. 27.  Bank Storage is the water which spreads out from the body of water, filling interstices of the surrounding earth and rock mass.
  28. 28.  The increased seismic activity is attributed to the changes in the normal effective stresses in the underlying rock because of the increased pore pressure. The transmission of the hydrostatic pressure through discontinuities in the underlying rock can have a triggering effect where a critical state of stress already exists.
  29. 29.  The most effective flood mitigation is obtained from an adequate reservoir located immediately upstream from the point (or reach) to be protected. A single reservoir may not be able to protect a number citied at a different distances downstream.  Economical analysis and other factors often favor the upstream site despite its lesser effectiveness,  No general rules can be set forth because each problem is unique, and several alternatives must be evaluated.  The use of several small reservoir offers the possibility of developing initially only those units of the system that yield the highest economic return and constructing the additional units as the development of the area increases the potential benefits.
  30. 30.  The life of a reservoir is predicted on the basis of the amount of sediment delivered to it, the reservoir size, and its ability to retain the sediment. Sediment deposition at the initial stage may be beneficial in the sense that it may have the effect of a natural blanket resulting in reduced seepage loss
  31. 31.  Stabilization of the unstable mass can also be achieved by strengthening or replacing weak material. Grouting is the most common remedy for strengthening such weak masses. It may be desirable to plan the steps to be taken to mitigate the effects of potential slide after it has occurred in spite of all preventive steps.
  32. 32. THANK YOU 
  33. 33.  Reservoirs-Factors-Affecting-Location.html   (images) References
  34. 34. Flood Damage mitigation Reservoirs Topics: Size of Reservoirs OperationProblems Reportedby: Edwardo R. Batas
  35. 35.  Are constructed in two main function: 1. First is to store water in the lake behind the dam to even out the fluctuations in river flow and match the availability in demand. 2. Second is to create a hydraulic head of water in the reservoir upstream of the dam so that water can be diverted into a canal and flow due to gravity. Dams
  36. 36. 1. Using a reservoir, the natural streamflow can be regulated so that the outflow follows the desired pattern. 2.To control flood. 3. To store water enough to sustain the demands on water during dry season. 4. Most probably as a source of energy such as Hydroelectric power. Why do we need reservoirs?
  37. 37. 1. Classification Based on Purpose -Single Purpose -Multi-Purpose 2. Classification Based on Size -Major Reservoir -Medium Reservoir -Minor Reservoir Classification of Reservoirs
  38. 38. 3. Classification Based on Storage - Seasonal storage reservoir - One-year reservoir
  39. 39. Okay Let’s Begin!!
  40. 40. 1. The potential reduction in peak flow by reservoir operation increases as reservoir capacity increases, since a greater portion of flood water can be stored. 2. For this reason a second criterion for evaluation of a flood-mitigation reservoir is its storage capacity. Size of Reservoirs
  41. 41. 3. It must no be presumed that the basic rule of design is “the bigger the better”, for the economic factors control the decision. 4. The maximum capacity required is the difference in volume between the safe release from the reservoir and the design and the design flood inflow.
  42. 42. Different Dams found in the Philippines
  43. 43. Location: Brgy. San Lorenzo, Norzagaray Bulacan Phils. Dam and spillways: Impound – Angat River Height: 131m (430 ft.) Length: 568m (1864 ft.) Width(base): 550m (1800ft) Reservoir: Creates- Angat Reservoir Total Capacity- 850 Million cu.m. Angat Dam
  44. 44. Location: Bokod, Benguet Type of Dam – Central Core Rock-fill Enbankment Impounds – Agno River Height – 129m Length – 452m Width(base) – 8.5m Spillways – 8 Reservoir Creates – Ambuklao reservoir Total capacity – 327, 170, 000 cu.m Active capacity – 258 , 000, 000 cu.m Catchment area – 690 Surface area – 7.7 AmbuklaoDam
  45. 45. Location : Pantabangan, Nueva Ecija Type of Dam: Enbankment, Earthfill Impounds: Pampanga River Height –107 m Length –1615m Elevation at Crest –232m Width(crest) – 12m Width(base) – 535m Dam Volume – 12 million cu.yd(9, 174, 658 cu.m.) Pantabangan Dam Reservoir Creates: Pantabangan Lake Total Capacity: 2, 996, 000, 000 cu.m Active Capacity: 2, 083, 000, 000 cu.m Catchment Area: 853 Surface Area: 69. 62 sq. km Normal Elevation: 230 m (755ft. Max)
  46. 46. Location: Greater Lagro, Quezon City Impounds – Tullahan River Total Capacity – 50.5 Million cu.m La Mesa Damand Reservoir Metro Manila and its sorrounding areas are divided into two water concessionaries : Maynilad water (red) and Manila water (blue)
  47. 47. SanRoqueDam Location: San Manuel and San Nicholas Pangasinan and Itagon, Benguet Phils. Dam And Spillways • Impounds- Agno River • Height – 200 m(660ft.) • Length – 1, 130 m (3,710ft.) Total Capacity – 835 million cu.m
  48. 48. 1. Streamflow forecast are necessary in planning reservoir operations for flood mitigation. 2. A flood mitigation reservoir has its maximum potential for flood reduction when it is empty. 3. Third operational problem develops when flows in excess of natural flows are released from a reservoir and synchronize at some point downstream with flood flows from a tributary. Operational Problems
  49. 49. References  Water Resources Systems Planning and Management by S.K. Jain and V.P. Singh  Wikipedia : Category, Dams in the Philippines  Google for Images
  50. 50. E.N.D