flooding and the ecology of streams
DESCRIPTION
Extreme weather is becoming more common in our region. Flood events can impact human health and safety, and result in substantial costs to property and infrastructure. Geared toward municipal decision makers and concerned citizens, this forum provides on-the-ground examples of flood resilience strategies that can help Hudson Valley communities minimize risks while conserving financial resources. Presentation by Dr. Stuart Findlay, Aquatic Ecologist, Cary Institute for a flood management forum hosted by the Cary Institute of Ecosystem Studies in Millbrook, NY on May 4, 2013.TRANSCRIPT
OUTLINE
• Floods are “normal” for streams and rivers• Physical effects and their legacies (long)• Connection to floodplains and watersheds• Consequences for organisms
Streams have long life-spans
• Roughly 10,000 years since glaciation – a local stream may have experienced a hundred 100-yr floods
Globally Low, declining or regulated flow more of an issue
Colorado River Delta. Nat GeographicTopping et al 2003
Nilsson et al 2005, Science
Locally – Increased Flows
• Wappinger Creek
1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 20200
50
100
150
200
250
300
350
400
450
500
Disc
harg
e (c
fs)
• Hudson
Annual
Summer
Wappinger Creek at Red Oaks Mill
0 50 100 150 200 250 300 350 400 450 500
Mean Annual Flow (CFS)
0
5
10
15
20
25
No
. o
f o
bs.
Mean Q 1st 25 yrs(240 cfs)
Mean Q last 25 yrs(292 cfs)
Causes of higher flow• More precipitation and/or intensity
• Vegetation
• Land-use, particularly impervious cover– Affects peak, timing and infiltration
FLO
W
TIME
Urban
Forested
Rain
Physical Legacies of High FlowsThe channel
Real life looks more complicated
Physical Legacies of High FlowsWood
Logs are re-distributed by floods
Floods increase connection to surroundings• Floodplains –
– Active movement of animals
• Floodplains – – Transport of debris
Floods increase connection to surroundings
• More strongly connected to more of the watershedFloods increase connection to surroundings
DRY
WET
DRY
WET
Chloride as an exampleRain event March 11-15, 2013
0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 408 432 456 48020
25
30
35
40
45
50
55
60
65
70
Stream Depth
Chloride (mg/L)
Consequences for Biota -A Tough place to live sometimes
Stream AlgaeSycamore Creek, AZ
Marti et al., 1997Valett et al. 1994
BugsMcMullen and Lytle 2012
Mayflies
DipteraCaddisflies
Stoneflies
SUMMARY/RE-CAP• Flooding will happen – plan for (more of) it• Flooding sets the physical template• Flooding is not ecologically harmful in the long run
– Floodplain/watershed connections– Biota have evolved under these conditions