Transcript PPT
A Survey of Major Watershed (RainfallRunoff) Models Knowing what is out there in the Workplace Capabilities of each model Requirements of each model What is the best model? Examples Ungaged area needing WRE management (expansion) Balancing $$, needs and requirements (Consulting) Flood-frequency analyses, forecasting, extrapolating for future scenarios Consider this Scenario: 1. A major expansion of urbanization is planned in forested land – malls, apts, parks, industry 2. How will the planned urbanization change the response of the land to rainfall? Increase chances of floods? Flashier? Bring down GWT? What kind of Water Resources Management Strategy/Measures would be needed to ensure longterm water needs? Watershed Models are used to answer such questions GOALS Be aware of the Major Models out there and their basic workings Understand Data needs and requirements Merits/Demerits of Models (situational) Ponder over: What is the Best Model? (open question) Be able to make an informed decision on the choice of a Model (for Consulting, Industry, Public Works) The Hydrologic Cycle All watershed Models (or Rainfall-Runoff) attempt to model the Hydrologic Cycle at the watershed scale. Watershed? – Natural System with all major components of cycle Hydrologic Cycle? (Water Cycle) – Water Distribution Model? – Abstraction of reality using Mathematics The Major Processes of a Model Infiltration Unsaturated Zone flow Groundwater (saturated zone flow) Overland Flow River Flow Evapotranspiration Rainfall is usually the major input in Hydrologic Models – it is not modeled! Classification of Models Based on mathematical representation of processes Conceptual Models Physically-based Models Based spatial nature of input/output of models Lumped Rainfall, Runoff, ET, GW flow Distributed Rainfall, Runoff, ET, GW flow Conceptual Vs Physically Based Conceptual Models – Idealization of processes as stores, buckets, parameterizations – simplified equations representing mass, momentum, energy. Physically-based Models – “rigorous numerical solution of partial differential equations governing flow through porous media, overland and channel flows. “ Lumped Vs Distributed Models Lumped - The spatial and temporal variation of meteorological, hydrological, geological and hydrogeological data across the model area is described as one aggregated value for input and output !All models are lumped at the finest scale! Distributed - The spatial and temporal variation of meteorological, hydrological, geological and hydrogeological data across the model area is described in gridded form for the input as well as the output from the model Data Requirements for Models Rainfall Data (Major Input) More Physically-based Soils Data (Infiltration, means more data Runoff) requirement DEM – channel network More Conceptual (River routing) requires less data! Vegetation Data (For ET) GWT Data (Saturated zone flow) Data acquisition is an investment Historical Rainfallthat needs to be commensurate Streamflow Data with the model (Calibration) Evaporation Data (ET) Sources of Data Rainfall – Gage, Radar (NWS), Satellite Soils – STATSGO, USDA DEM – USGS, Topo maps, Satellites Vegetation – Satellites, USDA Streamflow – USGS Reliability Ready availability Cost $$$ Resolution (space, time) Is all data needed? Physically-based – Insatiable needs – but potential high returns Conceptual – modest needs with modest returns Calibration –needs historical data. What is Calibration? What to do in ungaged regions where there is ‘No Data’? Transfer experience. PUB What affects $$ operational costs of a Model? Level of data needs – Data is expensive Level of physical complexity (Physically-based means qualified personnel; Rational Method – nobrainer Scale of the problem being addressed – larger/heterogenous – more $$$ The multiple needs of the TVA river reservoir system Some Models Out there HEC-1 PRMS HSPF (Fortran) MIKE 11 Make your own survey if you wish (Consider, DSS – Riverware, BASINS) For a comprehensive guide refer to: VP Singh – Computer Models for Watersheds HEC-1 Developed by Hydrologic Engineering Center (HEC) of US Army Corps of Engineers Flood Hydrograph Package – single storm even simulation. Lumped model Loss Function approach – SCS, Green Ampt, Holtan Data Needs – sub-basin delineation, rainfall, runoff, routing parameters Based on Unit Hydrograph or kinematic for runoff routing Other capabilities – Snowfall/melt, dam safety, pumping, diversions Customer Support? – Try HEC, San Diego, CA. PRMS – Precipitation-Runoff Modeling System Developed by USGS – more of an educational tool to build your own models Lumped/sub-basin –continuous simulation – see Handout Data needs – (depends) precip, streamflow, DEM, minmax air temp, radiation, vegetation..(see handout) Code in F77 Capabilities - many Customer Support? – Try USGS HSPF Hydrological Simulation Program - Fortran USGS – multi-use model Can do water quality. Mainly for land-use change, reservoir operations, flow diversions etc. Data needs – A lot – (see Hand-out) Software – In Fortran 77 Capabilities – A lot (see hand-out) Customer Support? – Try USGS Real Example – 62,000 sq mi tributary area in Chesapeake Bay. MIKE 11 Danish Hydraulic Institute DHI Very sophisticated – physically-based, high-end model Data needs – a lot (dependent of in-situ measurements Softwares – commercial (and expensive) Capabilities – Many (see hand-out) Customer Support? – Try DHI or Vendors Real Example – River Jamuna, Bangladesh MIKE SHE USGS – educational, conceptual/physical Data needs? Softwares Capabilities Merits/Demerits (can/can not do) Customer Support? Real Example - What is the best Model? This is situational – It All Depends! Primary objectives $$ budget Level of Tolerable Accuracy/precision Complexity and uniqueness of the problem Time frame for delivery Data availability It’s a highly complex question whose answer is sensitive to a multiplicity of factors Homework Problem Given watershed, Given data Given $$, deadline Choose your model (make strong arguments in favor of your choice over others)