Presentation on theme: "A Survey of Major Watershed (Rainfall- Runoff) Models z Knowing what is out there in the Workplace z Capabilities of each model z Requirements of each."— Presentation transcript:
A Survey of Major Watershed (Rainfall- Runoff) Models z Knowing what is out there in the Workplace z Capabilities of each model z Requirements of each model z What is the best model? z Examples yUngaged area needing WRE management (expansion) yBalancing $$, needs and requirements (Consulting) yFlood-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 long- term water needs? Watershed Models are used to answer such questions
GOALS zBe aware of the Major Models out there and their basic workings zUnderstand Data needs and requirements zMerits/Demerits of Models (situational) zPonder over: What is the Best Model? (open question) yBe 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 y Conceptual Models yPhysically-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 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 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!
Data Requirements for Models zRainfall Data (Major Input) zSoils Data (Infiltration, Runoff) zDEM – channel network (River routing) zVegetation Data (For ET) zGWT Data (Saturated zone flow) zHistorical Rainfall- Streamflow Data (Calibration) zEvaporation Data (ET) More Physically-based means more data requirement More Conceptual requires less data! Data acquisition is an investment that needs to be commensurate with the model
Sources of Data zRainfall – Gage, Radar (NWS), Satellite zSoils – STATSGO, USDA zDEM – USGS, Topo maps, Satellites zVegetation – Satellites, USDA zStreamflow – USGS z Reliability z Ready availability z Cost $$$ z Resolution (space, time)
Is all data needed? z Physically-based – Insatiable needs – but potential high returns zConceptual – modest needs with modest returns zCalibration –needs historical data. What is Calibration? zWhat to do in ungaged regions where there is No Data? Transfer experience. PUB
What affects $$ operational costs of a Model? The multiple needs of the TVA river reservoir system zLevel of data needs – Data is expensive zLevel of physical complexity (Physically-based means qualified personnel; Rational Method – no- brainer zScale of the problem being addressed – larger/heterogenous – more $$$
Some Models Out there zHEC-1 zPRMS zHSPF (Fortran) zMIKE 11 zMake your own survey if you wish (Consider, DSS – Riverware, BASINS) For a comprehensive guide refer to: VP Singh – Computer Models for Watersheds
HEC-1 zDeveloped by Hydrologic Engineering Center (HEC) of US Army Corps of Engineers zFlood Hydrograph Package – single storm even simulation. Lumped model zLoss Function approach – SCS, Green Ampt, Holtan zData Needs – sub-basin delineation, rainfall, runoff, routing parameters zBased on Unit Hydrograph or kinematic for runoff routing zOther capabilities – Snowfall/melt, dam safety, pumping, diversions zCustomer Support? – Try HEC, San Diego, CA.
PRMS – Precipitation-Runoff Modeling System zDeveloped by USGS – more of an educational tool to build your own models zLumped/sub-basin –continuous simulation – see Handout zData needs – (depends) precip, streamflow, DEM, minmax air temp, radiation, vegetation..(see handout) zCode in F77 zCapabilities - many zCustomer Support? – Try USGS
HSPF Hydrological Simulation Program - Fortran zUSGS – multi-use model zCan do water quality. zMainly for land-use change, reservoir operations, flow diversions etc. zData needs – A lot – (see Hand-out) zSoftware – In Fortran 77 zCapabilities – A lot (see hand-out) zCustomer Support? – Try USGS zReal Example – 62,000 sq mi tributary area in Chesapeake Bay.
MIKE 11 zDanish Hydraulic Institute DHI zVery sophisticated – physically-based, high-end model zData needs – a lot (dependent of in-situ measurements zSoftwares – commercial (and expensive) zCapabilities – Many (see hand-out) zCustomer Support? – Try DHI or Vendors zReal Example – River Jamuna, Bangladesh
MIKE SHE zUSGS – educational, conceptual/physical zData needs? zSoftwares zCapabilities zMerits/Demerits (can/can not do) zCustomer Support? zReal Example -
What is the best Model? This is situational – It All Depends! Primary objectives $$ budget Level of Tolerable Accuracy/precision Complexity and uniqueness of the problem Time frame for delivery Data availability Its a highly complex question whose answer is sensitive to a multiplicity of factors
Homework Problem zGiven watershed, zGiven data zGiven $$, deadline zChoose your model (make strong arguments in favor of your choice over others)