Flooding and the Ecology of Streams

Flooding Effects on Stream Ecology

Stuart FindlayFINDLAYS@CARYINSTITUTE.ORG

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

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Disc

harg

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• Hudson

Annual

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Wappinger Creek at Red Oaks Mill

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Mean Annual Flow (CFS)

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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

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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

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Chloride as an exampleRain event March 11-15, 2013

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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