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ERT 246 Hydrology & Water Resources Engineering

ERT 246 Hydrology & Water Resources Engineering. Siti Kamariah Md Sa’at School of Bioprocess Engineering, UniMAP. Unit Hydrograph. Cont. More Example 4:. Two storm each of 6-hr duration and having rainfall excess values of 3.0cm and 2.0 cm respectively occur successively.

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ERT 246 Hydrology & Water Resources Engineering

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  1. ERT 246 Hydrology & Water Resources Engineering Siti Kamariah Md Sa’at School of Bioprocess Engineering, UniMAP

  2. Unit Hydrograph Cont.

  3. More Example 4: • Two storm each of 6-hr duration and having rainfall excess values of 3.0cm and 2.0 cm respectively occur successively. • The 2-cm ER rain follows the 3-cm rain. The 6-hr UH for the catchment is the same as given in previous example. Calculate the resulting DRH. Page 3

  4. Unit Hydrograph of Different Durations • Under condition where lack of adequate data in developement of unit hydrograph • D-hour unit hydrograph is used to develop unit hydrographs of differing durations nD • Two method available: • Method of superposition • The S-Curve Page 7

  5. Method of superposition • If a D-h unit hydrograph is available, and its desired to develop unit hydrograph of nD, its is easily accomplished by superposing n unit hydrographs with each graph separated from the previous on by D-h. Page 8

  6. D = 2-Hr Unit Hydrograph Adjusted Net Rainfall one inch over basin Qp Page 9

  7. Change UH Duration • Consider 1 hr UH • Add and Lag two UH • by one hour • Sum and divide by 2 • Results in 2 hr UH Page 10

  8. Example 5 • Given the ordinates of a 4-hr unit hydrograph as below derive the ordinates of a 12-hr unit hydrograph for the same catchment Page 11

  9. Equilibrium Hydrograph Uniform Rain Inflow = Outflow Equiv to summing n hydrographs in T Produces S curve One Hydrograph Page 14

  10. S-Curve • Also known as S-hydrograph • Hydrograph produced by continous effective rainfall at a constant rate for infinite period. • Curve obtained by summation of an infinite series of D-h UH spaced D-h apart. Page 15

  11. S-Curve Construction • Obtained by adding a string of D-h UH each lagged by D-hours from one another. • If Tb= base period of the UH, addition of only Tb/D UH are suffcient to obtained S-curve • U(t) = S(t)-S(t-D) or S(t) = U(t)+S(t-D) Where • S(t-D)= S-curve addition at time t • S(t) = Ordinate of D-h UH at time t Page 17

  12. S-Curves for UH Page 18

  13. S-Curves S-curve • Convert 2 hr Unit hydrograph to 3-hr • Lag each 2-hr UH by Duration D • Add to produce S-curve Page 19

  14. Example 6 • Solve previous example (Example 5) with S-curve method: Page 20

  15. Hydrograph Convolution Add and Lag Method 1 2 3 1 2 STORM HYDRO 3 Add up the ordinates of all three to produce storm hydrograph Page 22

  16. NET RF Multi-Period Storm UH • Pg - F = Net Rainfall • RF units = UH duration (i.e. 1 hour) • Adjust UH by Net RF • Add and Lag UH • Produce Storm •    Hydrograph STORM Page 23

  17. Development Effects on UH Natural Partial Fully Developed Page 24

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