Autumn semester of Prof. Kim, Joong Hoon

Transcription

1 1 Autumn semester of 2010 Prof. Kim, Joong Hoon Water Resources Hydrosystems System Engineering Laboratory Laboratory

2 2 A. HEC (Hydrologic Engineering Center) 1 Established in the U.S. Army Corps of Engineers(USACE) Sacramento District 2 Early software packages a. HEC-1 (Watershed hydrology) b. HEC-2 (River hydraulics) c. HEC-3 (Reservoir analysis for conservation) d. HEC-4 (Stochastic streamflow generation) e. HEC-4 (Flood control and conservation systems) f. HEC-6 (Scour and depositions in reservoirs) B. History of Development 1 Separate programs : 1967 by Leo R. Beard 2 Major revision and unification : Second major revision : 1981 (Dam Breach, Kinematic Wave) 4 SPC versions : 1984 (partial), 1988 (full)

3 3 C. Current Versions: 1991, Version : extended memory support Version 4.1 : final release D. HEC NexGen Project Begins RAS, HMS, FDA, ResSim E. HEC-HMS - New GUI and Updates 1 First release April Version 1.1 released April Current Version 3.4 F. HEC-RAS - New GUI and Updates 1 Current Version 4.1

4 4 A. Hydrologic and Hydraulic s - In depth flood analysis of watershed system 1 Hydrologic modeling a. Hydrologic response : flow of a basin b. Hydrologic routing : the continuity equation and an analytical or an empirical relationship between storage within the reach and discharge at the outlet are analyzed c. HEC-1 and HEC-HMS 2 Hydraulic modeling a. Hydraulic response : water surface profiles of a stream b. Hydraulic routing : based on the solution of the partial differential equations of unsteady open channel flow. (Often the St. Venant equations) c. HEC-2 and HEC-RAS

5 5 A. Rainfall-runoff Meteological Total Subbasin Runoff Channel Routing Loss Computation Excess Precipitation Outlet Flow

6 6 B. Precipitation Depth Computation 1 Arithmetic mean 2 Thiessen polygon 3 Isohyetal C. Temporal Distribution of Precipitation ppattern ( t) PMAP () t = P ppattern ( t) t P pattern () t i ( ) i( ) ( ) w t p t = w t Ppattern(t) : temporal distribution of the MAP depth PMAP(t) : the watershed MAP at time t pi(t) : precipitation measured at gage i at time t wi(t) : weighting factor assigned to gage i at time t. i MAP

7 7 D. Spatial Distribution of Precipitation 1 Inverse-distance-squared Method a. Weight for the gage C w C = 1 2 dc d d d d C D E A wc : weight assigned to gage C dc : distance from node to gage C dd : distance from node to gage D in southeastern quadrant de : distance from nodeto gage E in southwestern quadrant df : distance from node to gage F in b. Weights for gages D, E and A are computed similarly. This computation is repeated for all times t. ( ) ( ) ( ) ( ) P () t = w p t + w p t + w p t + w p t P node A A C C D D E E node () t node ( ) node ( ) ( ) w t p t = w t node

8 8 E. Hypothetical Storms 1 Lack of coverage can complicate MAP estimation 2 Example of distribution of frequency-based hypothetical storm

9 9 F. HEC-1 - Calculates discharge hydrographs for a given rainfall event - Simulate the surface runoff response of a river basin 1 Parameter a. Particular characteristics of the component 2 b. Mathematical relations Lumped-parameter model a. Divides the watershed into subwatersheds and reaches b. Averaged values over the area c. Stream length for the mathematical coefficients G. HEC-2 1 Water Surface Profile program 2 One-dimensional water surface profiles 3 Backwater calculation 4 Based on a. Peak flow b. Roughness (Manning s) coefficients c. Cross-sectional geometry d. Bridges e. Culverts f. Stream length

10 10 A. Users Background - Hydrologic ing System - Easy-to-use graphical user interface (GUI) 1 Separate models a. Basin model : rainfall data b. Precipitation model : timing information c. Control model : time steps, start and stop date

11 11 Runoff Volume Initial and constant-rate SCS curve number (CN) Gridded SCS CN Green and Ampt Deficit and constant rate Soil moisture accounting (SMA) Gridded SMA continuous, distributed Direct-runoff s User-specified unit hydrograph (UH) Clark s UH Snyder s UH SCS UH Mod-Clark Kinematic wave Baseflow s Constant monthly Exponential recession Linear reservoir

12 12 Runoff Volume Initial and constant-rate SCS curve number (CN) Gridded SCS CN Green and Ampt Deficit and constant rate Soil moisture accounting (SMA) Gridded SMA continuous, distributed 1 Initial and constant-rate ( ) f = for P t I c ( ) f = f for P t > I f : infiltration rate(in/hr) P : rainfall intensity(in/hr) I : initial loss fc : initial infiltration rate(in/hr)

13 13 Runoff Volume Initial and constant-rate SCS curve number (CN) Gridded SCS CN Green and Ampt Deficit and constant rate Soil moisture accounting (SMA) Gridded SMA continuous, distributed 2 SCS curve number (CN) Q = ( P Ia ) ( ) a 2 P I + S 1000 S = 10, Ia = 0.2S CN CN : Runoff Curve Number Q : runoff, in P : rainfall, in S : potential maximum soil moisture retention after runoff begins, in Ia : initial abstraction, in

14 14 Runoff Volume Initial and constant-rate SCS curve number (CN) Gridded SCS CN Green and Ampt Deficit and constant rate Soil moisture accounting (SMA) Gridded SMA continuous, distributed 3 Green and Ampt Darcy s law with requirements of mass conservation Initial loss : interception, depression storage Excess precipitation Input - Initial loss - Volumetric moisture deficit - Wetting front suction - Hydraulic conductivity

15 15 Runoff Volume Initial and constant-rate SCS curve number (CN) Gridded SCS CN Green and Ampt Deficit and constant rate Soil moisture accounting (SMA) Gridded SMA continuous, distributed 4 Deficit and constant rate Quasi-continuous model of precipitation loss Initial loss can recover after a prolonged period of no rainfall Input - Initial deficit in inches (mm) - Constant loss rate in in/hr (mm/hr) - Maximum deficit in inches (mm)

16 16 Runoff Volume Initial and constant-rate SCS curve number (CN) Gridded SCS CN Green and Ampt Deficit and constant rate Soil moisture accounting (SMA) Gridded SMA continuous, distributed 5 Soil moisture accounting Continuous model that simulates both wet and dry weather behavior Represents the watershed with a series of storage layers

17 17 Runoff Volume Initial and constant-rate SCS curve number (CN) Gridded SCS CN Green and Ampt Deficit and constant rate Soil moisture accounting (SMA) Gridded SMA continuous, distributed 6 Gridded SMA continuous, distributed Specify a SMA unit for each gridded cell Same parameters as the SMA, but a gridded basis Only with the ModClark unit hydrograph

18 18 B. Unit Hydrograph 1 Definition - Sub-basin surface outflow due to unit (1-cm) rainfall excess applied uniformly over a sub-basin in a specified time duration 2 Duration of Unit Hydrograph - HEC-HMS sets duration equal to computation interval 3 Synthetic Unit Hydrographs a. SCS Dimensionless Unit graph b. Clark Unit Hydrograph (TC & R) c. Snyder Unit Hydrograph d. User-Defined Input UH e. Mod-Clark Unit Hydrograph

19 19 Direct-runoff models User-specified unit hydrograph (UH) Clark s UH Snyder s UH SCS UH Mod-Clark Kinematic-wave 1 User-specified unit hydrograph (UH) Basic Concepts and Equations Q n M = PU n m n m+ 1 m= 1 Qn : storm hydrograph ordinate Pm : rainfall excess depth Un-m+1 : UH ordinate

20 20 Direct-runoff s User-specified unit hydrograph (UH) Clark s UH Snyder s UH SCS UH Mod-Clark Kinematic-wave 2 Clark s UH s translation and attenuation of excess precipitation - Translation: movement of excess from origin to outlet - Attenuation: reduction of discharge as excess is stored in watershed

21 21 Direct-runoff models User-specified unit hydrograph (UH) Clark s UH Snyder s UH SCS UH Mod-Clark Kinematic-wave 3 Snyder s UH Standard UH t p = 5.5t r If the duration of the desired UH for the watershed of interest is significantly different from the above equation, tr tr tpr = tp 4 tr : duration of desired UH tpr : lag of desired UH

22 22 Direct-runoff models User-specified unit hydrograph (UH) Clark s UH Snyder s UH SCS UH Mod-Clark Kinematic-wave 4 SCS UH SCS suggests U p T p A = C T p A : watershed area C : conversion constant(2.08 in SI) t = + t 2 lag tlag : basin lag

23 23 Direct-runoff models User-specified unit hydrograph (UH) Clark s UH Snyder s UH SCS UH Mod-Clark Kinematic-wave 5 Mod-Clark Excess precipitation through a linear reservoir Lag time t S = K S 0 tc dcell cell = dmax All cells have the same reservoir coefficient K

24 24 Direct-runoff models User-specified unit hydrograph (UH) Clark s UH Snyder s UH SCS UH Mod-Clark Kinematic-wave 6 Kinematic-wave s watershed as a very wide open channel Inflow to channel is excess precipitation Often used in urban area S f y V V 1 V = S0 x g x g t

25 25 Baseflow s Constant monthly 1 Constantly monthly Constant flow : vary monthly Linear reservoir Exponential recession 2 Linear reservoir Conjunction with the continuous soil-moisture accounting (SMA) a linear function of the average

26 26 Baseflow s Constant monthly Linear reservoir Exponential recession 3 Exponential recession Qt = Qk 0 t Qt : baseflow at any time t Q0 : initial baseflow (at time zero) k: an exponential decay constant Initial baseflow recession Baseflow model illustration

27 27 Baseflow s Constant monthly Linear reservoir Exponential recession 3 Exponential recession Qt = Qk 0 t Qt : baseflow at any time t Q0 : initial baseflow (at time zero) k: an exponential decay constant Recession with multiple runoff peaks

28 28 C. Hydrologic Routing ; stream flow routing - A process to predict the temporal and spatial variations of a flood hydrograph as it moves S 1 Storage equation : I O=, I : inflow, O : outflow, S : storage t Discharge To Determine Travel Time Attenuation in peak Known Inflow Hydrograph Unknown Outflow Hydrograph Time

29 29 D. Routing in HEC-HMS Reach Routing s Kinematic wave Lag Modified Plus Muskingum Muskingum-Cunge Standard Section Straddle Stagger Reservoir Routing s Outflow Curve Outflow Structures Specified Release Elevation-storage Elevation-Area

30 30 D. Routing in HEC-HMS Reach Routing s Kinematic wave Lag Modified Plus Muskingum Muskingum-Cunge Standard Section Straddle Stagger 1 Kinematic Wave - Equation of continuity Q A + = q x t - Equation of momentum S = S 0 f Q : flow (m 3 /s) x : distance in flow direction (m) A : cross sectional area of flow (m 2 ) t : time (s) q : lateral inflow (m 3 /s/m) S 0 : gravity force term S f : friction force term 2/3 np α = S0 0.6, β

31 31 D. Routing in HEC-HMS Reach Routing s Kinematic wave Lag Modified Plus Muskingum Muskingum-Cunge Standard Section 2 Lag - Flow is delayed a fixed amount of time t lag. ( + lag ) = ( ) Qt t It t lag : flow time in the reach I : inflow to the reach Q : outflow from the reach Straddle Stagger

32 32 D. Routing in HEC-HMS Reach Routing s Kinematic wave Lag Modified Plus Muskingum Muskingum-Cunge Standard Section Straddle Stagger 3 Modified Plus - Input : storage-outflow relationship S - Output : storage indication + t S f = Si + QH Oi O 2 S : volume of storage in routing reach Si : storage indication at beginning of time Sf : storage indication at end of time interval QH : average inflow during time interval Oi : outflow at start of time interval Of : outflow at the end of time interval,

33 33 D. Routing in HEC-HMS Reach Routing s Kinematic wave 4 Muskingum Lag Modified Plus Wedge Muskingum Muskingum-Cunge Standard Section Straddle Stagger Pond S = KO + Kx(I-O) = K[xI+(1-x)O] O2 = C1 X I1 + C2 X I2 + C3 X O1

34 34 D. Routing in HEC-HMS Reach Routing s Kinematic wave Lag Modified Plus Muskingum Muskingum-Cunge Standard Section Straddle Stagger 5 Muskingum-Cunge Standard Section Pond Wedge X 1 Q = 1, 2 BS0c x K = x c c : flood wave celerity, ft/s Δ x : distance increment, ft X : weighting factor, non-dimensional. B : bottom width or average width, ft

35 35 D. Routing in HEC-HMS Reach Routing s Kinematic wave Lag Modified Plus Muskingum Muskingum-Cunge Standard Section Straddle Stagger 6 Straddle Stagger - Seldom used - Requires the number of ordinates to lag and the duration

36 36 A. Users Background - Calculating water surface profiles for steady gradually varied flow - Handle a full network of channels, a branching system, or a single river reach 1 Linear Routing : Flood routing a. Linear Muskingum b. Reservoir Storage-Indication / Modified Puls 2 Energy losses a. Friction loss b. Contraction/expansion loss 3 Momentum equation a. Hydraulic jumps b. Hydraulics of bridges c. Evaluate stream profiles