1. FLOOD ROUTING Flood Routing Techniques Siti Kamariah Md Sa’at PPK Bioprocess..2010

2. Flow Routing Procedure to determine the flow hydrograph at a point on a watershed from a known hydrograph upstream As the hydrograph travels, it attenuates gets delayed Q t Q t Q t Q t

3. Why route flows? Account for changes in flow hydrograph as a flood wave passes downstream This helps in Accounting for storages Studying the attenuation of flood peaks Q t

4. Types of flow routing Lumped/hydrologic Flow is calculated as a function of time alone at a particular location Governed by continuity equation and flow/storage relationship Distributed/hydraulic Flow is calculated as a function of space and time throughout the system Governed by continuity and momentum equations

5. Lumped flow routing Three types 1. Level pool method (Modified Puls) Storage is nonlinear function of Q 2. Muskingum method Storage is linear function of I and Q 3. Series of reservoir models Storage is linear function of Q and its time derivatives

6. S and Q relationships

7. Level pool routing Procedure for calculating outflow hydrograph Q(t) from a reservoir with horizontal water surface, given its inflow hydrograph I(t) and storage- outflow relationship

8. Wedge and Prism Storage Positive wedge I > Q Maximum S when I = Q Negative wedge I < Q

9. Hydrologic river routing (Muskingum Method) Wedge storage in reach Advancing Flood Wave I > Q Receding Flood Wave Q > I K = travel time of peak through the reach X = weight on inflow versus outflow (0 ≤ X ≤ 0.5) X = 0  Reservoir, storage depends on outflow, no wedge X = 0.0 - 0.3  Natural stream

10. Muskingum Equations Continuity Equation I - Q = dS / dt S = K [xI + (1-x)Q] Parameters are x = weighting and K = travel time - x ranges from 0.2 to about 0.5 where C’s are functions of x, K,  t and sum to 1.0

11. Muskingum Equations C 0 = (– Kx + 0.5  t) / D C 1 = (Kx + 0.5  t) / D C 2 = (K – Kx – 0.5  t) / D WhereD = (K – Kx + 0.5  t) Repeat for Q 3, Q 4, Q 5 and so on.

12. Reservoir Routing Reservoir acts to store water and release through control structure later. Inflow hydrograph Outflow hydrograph S - Q Relationship Outflow peaks are reduced Outflow timing is delayed Max Storage

13. Inflow and Outflow

14. I 1 + I 2 – Q 1 + Q 2 S 2 – S 1 2 tt 2 =

15. = change in storage / time ReRepeat for each day in progression Inflow & Outflow Day 3

16. Determining Storage Evaluate surface area at several different depths Use available topographic maps or GIS based DEM sources (digital elevation map) Outflow Q can be computed as function of depth for either pipes, orifices, or weirs or combinations

17. Typical Storage -Outflow Plot of Storage in vs. Outflow in Storage is largely a function of topography Outflows can be computed as function of elevation for either pipes or weirs S Q Combined Pipe

18. Comparisons: River vs. Reservoir Routing Level pool reservoir River Reach

19. Example 3: Level Pool Routing

20. Example 4: Resevoir Routing

21. Example 5: Flow Routing (Muskingum) Route the following flood hydrograph through a river reach for which K=12.0hr and X=0.20. At the start of the inflow flood, the outflow flood, the outflow discharge is 10 m 3 /s. Time (hr) 061218243036424854 Inflow (m 3 /s) 10205060554535272015