the hydromorphology of an urbanizing watershed using ... · the hydromorphology of an urbanizing...

The Hydromorphology of an Urbanizing

Watershed Using Multivariate Elasticity

Maura Allaire1, Richard Vogel2, and Charles Kroll3

1University of North Carolina-Chapel Hill; 2 Tufts University; 3 SUNY College of Environmental Science and Forestry

Outline What is hydromorphology?

New tool for hydromorphological problems

Surprising results from case study

Hydromorphology

Structure and evolution of hydrologic systems

due to complex interactions between

human and natural systems

Hydromorphology addresses human impacts

on hydrologic systems:

Climate Change

Land Use Water Use

Net Impact on Streamflow of simultaneous changes?

Urbanization Impacts on Low Streamflow?

• Imported water

• Stormwater detention

• Vegetation removal (↓ ET)

• Impervious surfaces

• Soil compaction

• Modified channels to convey precipitation

• Exported water

• Withdrawals of shallow groundwater

• Vegetation removal (↓ recharge, ↑ ET due to

heat advection)

Increase Low Flows

Decrease Low Flows

Net Impact?

Elasticity: responsiveness of one variable to another

New tool for hydrolorphological problems

%∆𝑌

%∆𝑋

Economics: If I lower the price, how much more will I sell?

Engineering: If precipitation increases, how will flood flows change?

more responsive

less responsive

New tool for hydrolorphological problems

Multivariate elasticity

Advantage: measures uncertainty (confidence intervals)

Climate Change

Land Use Water Use

Precipitation

P

GW Withdrawal

W

Population

L

wlpq WLP

where

Q

P

P

QP

Q

L

L

QL

Q

W

W

QW

Estimation of elasticities:

New tool:

Climate, Human Impacts, & Uncertainty

Stream

flow

(in cfs)

ε

95% CI

p

%SS

VIF

ε

95% CI

p

%SS

VIF

30

6

14

1.1 6.2

56

0.00

(2.900, 6.225)

6.3

1.131 4.563 -2.121

(0.310,1.953)

0.008

(-3.175, -1.066)

0.00

1.254

(-0.118, 2.627)

0.072

9

6.5

-0.331

(-1.202, 0.540)

0.450

2

Flood - Q max

Drought – Q 99

0.492

(0.324, 0.660)

0.00

90

1.1

Climate Land Use Water Use

Precipitation, PWatershed

Population, L

Well Withdrawals,

W

P L W

Land Use Water Use Climate Change

Greater uncertainty in

land and water use

Case Study: Aberjona River

Northwest of Boston

24 sq. miles

Urbanized basin

Urbanization impacts on complete range of streamflow (low, avg., flood)

Aberjona River, Massachusetts

Results: Continual increase in flood flows

All flows increase due to urbanization,

not only floods

Low flow

Stream

flow

(in cfs)

ε

95% CI

p

%SS

VIF

ε

95% CI

p

%SS

VIF

30

6

14

1.1 6.2

56

0.00

(2.900, 6.225)

6.3

1.131 4.563 -2.121

(0.310,1.953)

0.008

(-3.175, -1.066)

0.00

1.254

(-0.118, 2.627)

0.072

9

6.5

-0.331

(-1.202, 0.540)

0.450

2

Flood - Q max

Drought – Q 99

0.492

(0.324, 0.660)

0.00

90

1.1

Climate Land Use Water Use

Precipitation, PWatershed

Population, L

Well Withdrawals,

W

P L W

Land Use Water Use Climate Change

Surprising Impacts on Low Flows

Low flows more

sensitive to human

impacts than floods (changes in precip.,

population & water use)

Urbanization leads to increased low flows (not previously demonstrated)

Results: Case Study

Future hydromorphological changes could increase avg. annual

streamflows and low flows (i.e. lessen droughts) more than floods

Climate Change

Land Use Water Use

Net Impact on Streamflow:

↑Floods, ↑ Avg. Flows, ↑ Low Flows Low flows most sensitive

to human impacts

Take-Away

1. Streamflow is sensitive to climate, land use & water use

Must consider these 3 changes simultaneously

2. New tool (multivariate elasticity) accounts for simultaneous changes

Can be applied to variety of hydromorphological &

socio-hydrological problems

3. Low flows extremely sensitive to changes in hydromorphology

More studies needed to generalize result

Questions?

Maura Allaire mallaire@live.unc.edu

“The Hydromorphology of an Urbanizing Watershed Using Multivariate Elasticity”