Transcript Hydrology of a Flash Flood

Distributed Hydrologic Modeling
Baxter E. Vieux, Ph.D., P.E., Professor
School of Civil Engineering and Environmental Science
University of Oklahoma
202 West Boyd Street, Room CEC 334
[email protected]
405.325.3600
Biosketch
Dr. Baxter E. Vieux, PhD, P.E. is a professor in the School of Civil Engineering and
Environmental Science, University of Oklahoma. He specializes in the integration of
computational hydrologic methods and visualization with Geographic Information Systems
(GIS). Applications include simulation of water quality and flooding using WSR-88D radar
estimates of rainfall. He was recently named Director of the International Center for Natural
Hazards and Disaster Research, University of Oklahoma. Efforts to reduce impacts on civil
infrastructures due to severe weather are being undertaken by this center with an initial
focus on flooding. Prior to joining the faculty at the University of Oklahoma, he was a
Visiting Assistant Professor at Michigan State University. He has performed consulting and
collaborative research with agencies and private enterprises in the US and abroad in Japan,
France, Nicaragua, and Poland. Over fifty publications appearing as book chapters (2),
refereed journal articles (14, 3 in press), and conference proceedings (35, 2 in press) have
been authored including a forthcoming text for Kluwer entitled: Distributed Hydrology
Using GIS (expected 2000). He has been on the Editorial Board of Transactions in GIS since
1995, serves on the American Society of Civil Engineers Council on Natural Hazards and
Disasters, and is Fellow and member of the Advisory Council of the Cooperative Institute
for Mesoscale Meteorological Studies at the University of Oklahoma. He is a member of
ASCE, NSPE, AGU, and AMS, Tau Beta Pi, Phi Kappa Phi, and ASEE. Prior to his
academic career, ten years were spent in Kansas and Michigan with the USDA-Natural
Resources Conservation Service (formerly, USDA-SCS) supervising design and
construction of drainage, irrigation, soil conservation, and flood control projects .
Recipe for a flood
Ingredients—
Take a generous amount of rainfall
Presoak the soil so it is saturated
Add generous amounts of rainfall
Stand back
What’s wrong with this picture?
Flood disasters
More disasters
What constitutes a flash flood
No firm criteria exist to discriminate
between fast response and river floods
Response time in the range of 1-6 hours
As opposed to river floods, flash floods
have a quick response to rainfall input
Upland basins are most likely killers
Slow-rise river floods have highest
economic impact
Flooding
Country
Mozambique
Venezuela
India (Orissa)
China
Bangladesh
Date
Mar-00
Dec-99
Nov-99
Aug-98
Sep-98
Deaths
400
30,000
10,000
3,600
4,750
People
Affected
2m
0.6m
12m
200m
23m
Economic
Cost
($bn)
NA
15
2.5
30
5
• Last year natural disasters killed an estimated 100,000
people.
• In a typical year, floods claim half the victims of the
world’s natural disasters.
--The Economist, 11March 2000
Enabling Technologies
Ingest, storage and processing of data streams
from radar, satellite and other mesonet sensor
systems
Radar, automated sensors, remote sensing
platforms are next generation technologies
providing new data and information for mitigating
the impact of flooding and drought
Improved modeling, warning and information
dissemination technologies
Why does one basin flood and
another doesn’t
Efficient drainage network
Debris clogged main channel
Denuded landscape or burned vegetation
Urbanization effects on time and volume
Steep topography
Heavy rain over large areas
Basin Characteristics
Factors that affect the basin response are—
Drainage area
Drainage network
Slope
Channel geometry and roughness
Overland flow and roughness
Vegetative cover
Soil infiltration capacity
Storage capacity
Runoff Mechanisms
There are two runoff producing
mechanisms:
1.
2.
Infiltration excess
Saturation excess
Mountainous watersheds tend to be
dominated by saturation excess.
Infiltration excess dominates runoff in
flatter agricultural watersheds.
Saturation Excess
Rain
Saturation Excess
Phre
atic S
urfac
e
Infiltration Excess
Rain
Ru
n
off
R<I
Infiltration
R>I
Infiltration Excess
9
9
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
0
00 1 12 2 33 44 5 56
Time (hr)
Infiltration Rate (in/hr)
Rainfall Intensity (in/hr)
Horton Infiltration Equation
Rain
Infil
Hydraulics of Runoff
Two basic flow types can be recognized:
Overland flow
This is conceptualized as thin sheet flow
before the runoff concentrates in recognized
channels.
Channel flow
The channel has hydraulic characteristics
that govern flow depth and velocity.
Lumped modeling approach
The following slides show how a lumped model
may be used with distributed rainfall derived from
WSR-88D
There were no rain gauges in the vicinity of the
basin.
Flood magnitudes were modeled for design of a
bridge and roadway re-alignment for the
Oklahoma Department of Transportation
Cottonwood Creek
Storm Total Oct 30 - Nov 1, 1998
Cottonwood Watershed
Storm Total Contours
HEC-HMS Model
Cottonwood Basin, Alfalfa County Oklahoma
10/30/98 - 11/01/98
0.5
Rainfall (in)
0.4
0.3
0.2
0.1
0
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71
Time (h)
Hydrograph
HEC-HMS 50-Year Storm
SCS CN increased from 79 to 90
Rainfall increased by 20%
Distributed Model Advantages
Distributed has advantages because the spatial variability
of precipitation input and controlling parameters are
represented in the model.
Incorporating spatial variability in a distributed model
reduces the prediction variance.
Physics-based models are generally more responsive to
radar input than lumped models.
River basin models based on 6-hour unit hydrographs are
not suitable for basins with response times less than 6
hours.
Distributed models require fewer storm events for
calibration than lumped
Overall Goal
The overall goal of distributed hydrology is
to better represent the spatially distributed
processes using maps of parameters and
precipitation input.
Distributed models tend to have better
prediction variance than lumped models.
Applications include simulation of flash
floods, soil moisture, water resources.
Runoff Simulation
Grid Cell Resolution
Finite Elements
Connectivity
Watershed
Runoff
Simulation
Rainfall
Runon
Runoff
Runon
Infiltration
* Rainfall excess
at each cell
- Soil infiltration rate
- Rainfall rate
- Runon from upslope
Flow
Characteristics
Channel Characteristics
Stream
- Cross-Section Geometry
- Slope
- Hydraulic Roughness
Overland
Direction
Digital Elevation Model
Resolution
1080 meter
60 meter
Digital Watershed
Model Equations
 h  s1/2 . h5/3  γ.R  α.I
 t βn  x
INPUT
Discharge Hydrograph
Radar Rainfall (R)
250
Runoff
Land surface

h

200
150
100
50
Time (hrs)
Hydraulic Roughness (n)
96
72
48
Soil Infiltration (I)
24
0
0

300
Discharge (cfs)

OUTPUT
Runoff Flow Rates
Depth h is measured perpendicular to the bed and
the velocity, V is parallel to the landsurface.
Continuity equation— q  V * h
c 0 .5 5 / 3
Manning Equation— q  S o h
n
n
So
c
=
=
=
hydraulic roughness
land surface slope
1 for metric, 1.49 english
Blue River Basin
• The 1200 km2 Blue River basin was
delineated from a 3-arc second
digital elevation model
• Aggregated to grid cell size = 270 m
• Hydrographs simulated for each
sub-basin
• Runoff is computed for each grid cell
• Routed downslope through each cell
eventually reaching the stream
network and basin outlet
Lumped Versus Distributed
Lumped modeling represents the basin and
precipitation characteristics using single
values of roughness, slope, and rainfall over
each sub-basin.
Distributed modeling represents the spatial
variability within each sub-basin or basin
using grid cells, TINS or other
computational element.
Lumped model?
Research efforts
1.
2.
3.
4.
5.
6.
Soil moisture with feedback (SHEELS)
Data assimilation (LDAS/AMSR)
Real-time radar (QPESUMS)
Nonpoint water quality simulation of phosphorus
transport
Calibration using optimal control theory-Optimal
values are identified by comparing simulated and
observed hydrographs
Radar/Rain gauge calibration using the river
basin as validation…
Any Questions?