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Hydrology of Fast Response Basins
Baxter E. Vieux, Ph.D., P.E.School of Civil Engineering and Environmental Science
University of Oklahoma202 West Boyd Street, Room CEC334
Norman, OK 73019 [email protected]
Biosketch
Dr. Baxter E. Vieux, PhD, PE specializes in the integration of computational methods and visualization with Geographic Information Systems (GIS). Applications include simulation of water quality and flooding. 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 the rainfall to steeply sloping land
Look out!
Flood Statistics
Flooding is the most deadly and costly of all natural disasters.
Read the document Summary of Natural Hazard Statistics.
From this document what would you conclude to be the single most important factor that might cause death during a flood?
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
Read the document flash floods.
Flooding
Country Date Deaths PeopleAffected
EconomicCost($bn)
Mozambique Mar-00 400 2m NAVenezuela Dec-99 30,000 0.6m 15India (Orissa) Nov-99 10,000 12m 2.5China Aug-98 3,600 200m 30Bangladesh Sep-98 4,750 23m 5
--The Economist, 11March 2000
• 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.
Enabling Technologies
Ingest, storage and processing of data streams from radar, satellite and other mesonet sensor systemsRadar, Mesonets, remote sensing platforms are next generation technologies providing new data and information for mitigating the impact of flooding and droughtImproved modeling, warning and information dissemination technologies
WSR-88D or NEXRAD
• Weather Surveillance Radar-1988 Doppler
• Prototyped in Norman at NSSL
• Scans Every 5 or 6 minutes during precipitation
• 150+ installed in US and abroad
0.5°
1.5°2.5°
Why does one basin flood and another doesn’t
Efficient drainage network
Debris clogged main channel
Denuded or burned vegetation
Urbanization effects on time and volume
Steep topography
Heavy rain over large areas
Read the document Flash Flood Factors.
Basin Characteristics
Factors that affect the basin response are—
Drainage areaDrainage networkSlopeChannel geometry and roughnessOverland flow and roughnessVegetative cover Soil infiltration capacityStorage capacity
Hydraulics
Hydraulics of overland and channel flow
Turbulent flow
Chezy or Manning
Conservation of momentum and mass
Discharge computations using conservation equations is the basis for distributed hydrologic modeling.
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.
Runoff Mechanisms
There are two runoff producing mechanisms:
1. Infiltration excess
2. Saturation excess
Mountainous watersheds tend to be dominated by saturation excess.
Infiltration excess dominates runoff in flatter agricultural watersheds.
Phreatic Surface
Saturation Excess
Rain
Saturation Excess
Rain
Runoff
Infiltration Excess
R > IR < I
Infiltration
Infiltration Excess
Horton Infiltration Equation
0
1
2
3
4
5
6
7
8
9
0 0 1 1 2 2 3 3 4 4 5 5 6
Time (hr)
Ra
infa
ll In
ten
sit
y (
in/h
r)
0
1
2
3
4
5
6
7
8
9
Infi
ltra
tio
n R
ate
(in
/hr)
Rain
Infil
Probabilistic Concepts
Key concepts--
Intense rainfall happens infrequently
The return period is inversely proportional to the frequency of being equaled or exceeded.
Intensity-Duration-Area-Frequency
fT /1
Regional Frequency Analysis
Using regression analysis applied to stream gauge records, we can estimate the discharge associated with a particular frequency.
Most states have developed regression equations for ungauged basins.
For example in Oklahoma given the drainage area, A, in sq.mi. and the 2-year 24-hour storm depth, I, in inches we can calculate:
USGS Regression Equations for Oklahoma
For Cherokee County, the 2-year 24-hour rainfall is 3.5 inches. Calculate the following for the Cottonwood Basin:
A= 49 sq mi
I = 3.5 inches
06.119.0100
14.120.050
00.227.02
95.1
58.1
18.0
IAD
IAD
IAD
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.
Cottonwood CreekStorm 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
0.1
0.2
0.3
0.4
0.5
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)
Rai
nfa
ll (i
n)
Hydrograph
HEC-HMS 50-Year Storm
SCS CN increased from 79 to 90
Rainfall increased by 20%
Rainfall
Infiltration
Runon Runon
Runoff
Stream
Overland
Direction
Flow Characteristics Channel Characteristics
- Cross-Section Geometry- Slope- Hydraulic Roughness
* Rainfall excess at each cell
- Soil infiltration rate - Rainfall rate - Runon from upslope
Grid Cell Resolution Finite ElementsConnectivity
Watershed Runoff Simulation
Runoff Simulation
OUTPUT
Discharge Hydrograph
0
50
100
150
200
250
300
Time (hrs)
Dis
charg
e (
cfs
)
Radar Rainfall (R)INPUT
Land surface
Soil Infiltration (I)
Hydraulic Roughness (n)
α.Iγ.Rx5/3h.
nβ1/2s
th
h
Runoff
Model Equations
Runoff Flow Rates
Depth h is measured perpendicular to the bed and the velocity, V is parallel to the landsurface.
Continuity equation—Manning Equation—
n = hydraulic roughness
So = landsurface slope
c = 1 for metric, 1.49 english
hVq *3/55.0 hS
n
cq o
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
Sensitivity to Initial Conditions
0
100
200
300
400
500
600
113 114 115 1161996 Day of Year
Dis
char
ge (m
3/s
)
0% Initial water content50%70%90%95%100%
Δ10%
Δ32
S
Q
i
Distribute 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.
Self Examination
Label the following with a + or – according to the effect on flood levels at a given location—
Debris clogged main channel
Denuded or burned vegetation
Urbanized landsurface conditions and channels
Steep terrain
Clayey soil
Dry intial moisture conditions
--Ganges River Distributary, Bangladesh
Questions...