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Unisys
March 1, 2017
Unisys
NWS
USGS
Q, cfs
Ppt,
in.
USGS
Q, cfs
Ppt,
in.
Bob Criss Washington University
Scale Dependence of FloodsRainfall-Runoff ModelEnvironmental ConsequencesHuman Aggravation of FloodsRecommendations
Flash Flood Processes and Consequences in
Small Watersheds
NASA Landsat
JEFFERSON CITY looking South S
MODOT/USGS
Jefferson City, 7/30/93
Criss
Missouri River at Hermann 1993 data from USACE
YearDay, 1993
Stage, ft.
750,000 cfs
150,000 cfs
69,400 cfs
232,000cfs
522,500 sq. mi5x in 7 days
Big River 9/25/99 ~ 100 cfs Criss
Big River, 4/29/96 following 4.5” rain on 4/28 ~ 26,100cfs
Criss
Criss
Big River at Brynesville April-June 1996
data from USGS
443 cfs
26100cfs
917 sq. mi30 x in 1 day
Deer Ck bridge at McKnight Rd 10/12/2008
Criss
Deer Ck bridge at McKnight Rd 9/14/2008
0
5
10
15
20
25
5 10 15 20
Deer Creek at MaplewoodSt. Louis County USGS # 7010086
Sta
ge,
ft
September 2008
36.5 sq mi2,000x in 6 hrs
10,300 cfs
5 cfs
-1
0
1
2
3
4
5
-1 0 1 2 3 4
Log
Q cfs
Log A m i2
Mean Flowsslope 1:1
Peak Flowsslope 0.57:1
Missouri
updated after Criss 2003
EW Gateway
East St Louis
9/14/08
9/22/93
7/10/91
8/12/934/29/96
5/17/956/20007/20047/15/93
9/23/93
8/22/96
Criss
Flash Floods in Small Basins1. Develop very suddenly
2. Occur frequently, close to people
3. Cause large damages and fatalities4. Feature large stage increases, comparable to those of large watersheds5. Have peak flows 100 to 1,000x greater than normal flows6. Estimates of flow magnitudes and flood
frequencies are too low
Summary: Part 1
Criss
b = 0.5
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5
Q/Q
p
Time, days
0.25
0.5
1.0
b=2.0
SYNTHETIC HYDROGRAPHtp = 2b/3
after Criss (2003)
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5
SYNTHETIC HYDROGRAPHV
t = 4.3 b Qp
Q
Time, days
b=0.25
0.5
1.0b=2.0
Criss
Human Aggravation of Flash Floods
Basic Observations (Small Basins)
Criss
Criss
Fishpot CreekValley Park
CrissCaulks Creek
Human Aggravation of Floods:Small Basins1. Erosion, Channel Widening & Deepening2. Disconnection of Channel from Floodplain3. Coarse Sediments4. Loss of Perennial Flow5. High Peak Flows6. Habitat Destruction
0
0.2
0.4
0.6
0.8
1
0 1 2 3 4 5
SYNTHETIC HYDROGRAPHV
t = 4.3 b Qp
Q
Time, days
b=0.25
0.5
1.0b=2.0
Criss
Natural => Urban BasinsSHORTER TIME CONSTANT
What are we doing wrong?Why are Time Constants Shorterin Developed Areas?
9/22/08
Black Creek
Upper Two Mile Creek4/7/13
Upper Two Mile Creek10/20/12
Williams Creek
Criss
New DevelopmentWilliams Creek watershed
Wilson 2009
9/14/08
9/22/93
7/10/91
8/12/934/29/96
5/17/956/20007/20047/15/93
9/23/93
8/22/96
Criss
SMALL BASINS Too much impervious surface; thin soils Destruction of Riparian Borders Undersized Culverts & Bridges Accelerated rainfall delivery to streams Storm sewers Channelization Understated Risk Floodplain development
What are we doing wrong?
Floods are acts of God, but flood damages are acts of man.
1. More Fundamental Research2. Gaging of Small Natural Basins3. Stormwater Management: Delay or Divert Rain Barrels, Detention Basins, Rain Gardens Diversion to major rivers
4. Avoid debauching storm sewers into local streams
Recommendations
Green infrastructure: Incorporate soil and vegetation into the
urban or suburban landscape. Current approaches
green roofs trees and tree boxes rain gardens rain barrel or cisterns vegetated swales pocket wetlands infiltration planters vegetated median strips reforestation protection and enhancement of riparian buffers protect floodplains
EPA 2008
Deer Creek Alliance