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DESIGN OF A GRAVITY DAM A case study of River Nyamamithi in Naivasha constituency

DESIGN OF A GRAVITY DAM A case study of River Nyamamithi in Naivasha constituency. F21/2500/2009. MWAURA WILSON NJENGA. Overview. Background information.

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DESIGN OF A GRAVITY DAM A case study of River Nyamamithi in Naivasha constituency

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  1. DESIGN OF A GRAVITY DAM A case study of River Nyamamithi in Naivasha constituency F21/2500/2009 MWAURA WILSON NJENGA

  2. Overview

  3. Background information • Surface runoff is the water flow that occurs when the soil is infiltrated to full capacity and excess water from rain, melt water, or other sources flows over the land. • Infiltration excess overland flow. This occurs when the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground, and any depression storage has already been filled.

  4. cont • Saturation excess overland flow. When the soil is saturated and the depression storage filled, and rain continues to fall, the rainfall will immediately produce surface runoff.

  5. PROBLEM STATEMENT

  6. Contmap of lake naivasha catchment

  7. Site Analysis

  8. Objectivesoverall objective • Reduce the runoff problem in Naivasha. Specific objectives • Determine the total volume of water from the catchment • Design a gravity dam

  9. Literature review • Gravity dam is a structure so built that it derives its stability from its own weight to resist external forces • They transfer their weight to the ground by cantilever action and require strong rock foundation

  10. Theoretical framework • The rational method Q= 0.0028CIA This was used to calculate the total amount of runoff from the catchment area • Tc= 0.01947L0.77S-0.385 Kirpichs equation was used to calculate the time of intensity.

  11. cont • The cone formula was used to calculate the total volume of the reservoir • Gravity dam equations • Hydraulic height (H) =highest contour – lowest contour • Freeboard (FB) = 1.33hw or 5%H • Structural height (Ht)=H+ FB • Top width (Tw) =0.14Ht or 0.55H0.5

  12. Methodology • Reconaissance survey and topographical surveys were conducted • Led to identification of suitable site for dam construction • River catchment area was estimated using Google earth pro • Runoff coefficient for the catchment were determined

  13. Cont • The peak runoff rate was determined • The total volume of water from the catchment was calculated • A contour map of the reservoir area was prepared • Total volume of water the reservoir can hold was calculated

  14. Cont • The gravity dam dimensions were determined • The dam was checked for stability, tension, sliding and compression.

  15. Results and Discussion

  16. cont

  17. cont • Hydraulic height (H) = 2333 – 2330 = 3m • Freeboard (FB) = 1.33hw or 5%H = 1m m

  18. cont 3) Structural height (Ht)= H + FB = 4M 4) Top width (Tw) = 0.14Ht or 0.55H0.5 = 1M 5) Base width (b) = 3m

  19. cont • initial dam dimensions

  20. Dam stability analysis • Overturning R.m=36.768t.m o.m=(9+2.71+5.833+4.5) = 22.043 t.m = 36.768/22.043=1.66 1.66>1.5, thus dam is safe • Compression/crushing. pntoe=9.8t/m2 = 0.98*10^5N/m2 f= 83.333*10^5N/m2 pntoe<f (thus dam is safe)

  21. cont • Tension e= 0.5m and b/6= 3/6= 0.5m e=b/6, thus dam is safes safe

  22. Autocad drawing

  23. Catchment characteristics

  24. Catchment sketch

  25. Runoff computation • Runoff volume (m3 ) = runoff depth (m) * catchment area (m2)The runoff coefficient method was used to calculate depth R= C.P C= runoff coefficient p= rainfall (mm) (from climwat) Depth= 9.35mm Total volume= 63,011.37 m3

  26. Digital elevation model

  27. contours

  28. conclusion • The ultimate goal of this project was to design a gravity dam for flood control on River Nyamamithi. It can be concluded that this projects objectives were achieved as the detailed design of the concrete gravity dam was achieved. The dam has a height of 4m above the foundation and creates a reservoir storage of 57746 m3, this is sufficient to control the downstream flooding.

  29. References • Auto cad civil 3D 2010, pipelines from alignments, profiles and corridors, Jack Strongitharm, Autodesk ltd, July 2009 • Becht R, Odada EO, Higgins S(2005) lake naivasha: experience and lessons learned brief. Managing lakes and basins for sustainable use: a report for lake basin managers and stakeholders. • Design manual for concrete gravity dams, a water resources technical publication, Denver, Colarado, 1976. • http://en.wikipedia.org/wiki/surface_runoff. • King and Brater: Handbook of Hydraulics, Mcgraw Hill Book Company, Inc., New York, Fifth Edition 1963. • Merritt: Standard Handbook for Civil Engineers, Mcgraw Hill Book Company, Inc., New York, 1968 • Otiang’a owiti GE, oswe IA.(2007) human impact on lake ecosystems: the case of lake Naivasha, Kenya. African journal of aquatic science 32:79-88 • River weirs- good practice guide, Charles Rickard, Rodney Day, Jeremy Purseglove. • Streeter: Fluid Mechanics, Mcgraw Hill Book Company, Inc., New York, Fifth Edition. • The physical attributes of the Lake Naivasha catchment rivers, Mark Everard, Jacqueline A. Vale, David .M.Harper and Hakan Tarras-Wahlberg • Training on design of hydraulic structures, module 3, design of weirs and pumps, Zemene Tsehay, September 2009, Bahir Dar.

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