Presentation on theme: "Hydrologic Simulation Models"— Presentation transcript:
1 Hydrologic Simulation Models Hydrology and Floodplain Analysis, Chapter 5CEVE 412Dr. Phil Bedient
2 Introduction to Hydrologic Models Hydrology and Floodplain Analysis, Chapter 5.1Introduction to Hydrologic Models
3 Factors in Hydrographs In order to create an accurate model one first needs to understand all of the relevant factors in the watershed.
4 History of Computer Models Harvard, Stanford, and the U.S. Army Corps of Engineers pioneered hydrologic computer modeling.The first available model was: Hydrologic Simulation Program – FORTRAN (HSPF)1970sIncreasing interest in water quality spurred more models.
5 History of Computer Models Breakdown of computer modeling software packages.
6 Steps in Watershed Modeling Hydrology and Floodplain Analysis, Chapter 5.2Steps in Watershed Modeling
7 Steps in Watershed Modeling 1. Select model based on study objectives and watershed characteristics, availability of data, and project budget.2. Obtain all necessary input data—rainfall data, digital topography, land use and soils, infiltration, channel characteristics, streamflow data, design floods, and reservoir data.3. Evaluate and refine study objectives in terms of simulations to be performed under various watershed conditions.
8 Steps in Watershed Modeling 4. Choose methods for determining subbasin hydrographs and channel routing. 5. Calibrate model using historical rainfall, streamflow, and existing watershed conditions. Verify model using other events under different conditions while maintaining same calibration parameters.
9 Steps in Watershed Modeling 6. Perform model simulations using historical or design rainfall, various conditions of land use, and various control schemes for reservoirs, channels, or diversions, to the extent possible. 7. Perform sensitivity analysis on input rainfall, routing parameters, and hydrograph parameters as necessary. 8. Evaluate usefulness of the model and comment on needed changes or modifications.
10 Description of Major Hydrologic Models Hydrology and Floodplain Analysis, Chapter 5.3Description of Major Hydrologic Models
17 Capabilities of HEC-HMS Simulation of watershed runoff and streamflow.Determination of flood flows at various locations.Evaluation of land use or topographic changes.Simulation of flood control measures.Computation of damage frequency curves.
18 Watershed Delineation and Organization HEC-HMS uses parameters averaged in space and time to simulate the runoff process.Each watershed is divided into relatively small homogeneous subbasins because of the limitations of UH theory.1-10 mi2 per subbasin
19 PrecipitationP is computed for each of those subbasins from either historical or synthetic storms.Can be input in many different forms:Incremental P for a time in each subbasinTotal cumulative P and time distributionHistorical gage data and areal weighting (Thiessen) coefficients for each subbasinHEC-HMS can also do snowfall and snowmelt.
20 Example Watershed in HEC- HMS with precipitation
21 Loss Methods Initial and Constant HEC exponential SCS Curve Number Holtan MethodGreen and AmptDeficit/ConstantSoil Moisture Accounting
22 Subbasin Runoff Calculation Clark hydrograph method (TC&R method)Snyder unit hydrograph methodSCS method (CN method + SCS UH)Kinematic wave for overland hydrographModClarkUser-specified S-graph
23 Family of 1hr UHs The larger the TC value the flatter the UH response. 80% Devel.SCS curve # 94The larger the TC value the flatter the UH response.
24 Baseflow Calculation Three parameters: Q0 flow in channel prior to start of rising limbRatio of recession flows at t=1 (RTIOR)QR recession thresholdQ0 = starting baseflowQ = baseflow rate at end of nΔTRTIOR = ratio of recession flows at t =1 hr increment apart.
25 Baseflow CalculationFor urban channels it can work to just use a constant value.Brays Bayou, Houston
26 Flood RoutingFlood routing analyzes the movement of a flood wave as it travels from reach to reach through a stream or river.Methods for Flood Routing in HEC-HMSMuskingumModified PulsKinematic WaveMuskingum – Cunge 8-pointLag
27 Application of HEC-HMS Watersheds Hydrology and Floodplain Analysis, Chapter 5.5Application of HEC-HMS Watersheds
28 History of HEC-HMS HEC-1 Watershed Hydrology (1981) There has since been HEC-2, HEC-3, HEC-4There have been numerous other HEC releases.HEC-HMS, HEC-RAS, HEC-GeoRAS, HEC-SSP, HEC-RPT, HEC-ResSim, HEC-ResPRM, HEC-EFM, HEC-FDA, HEC-DSSHEC-HMS (1998, 2006, 2010)Major releases: 1998, 2006, 2010
29 HEC - HMS A project consists of three separate parts: The Basin model The meteorological modelThe control specifications