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

Google

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