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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 [email protected]
“The Hydromorphology of an Urbanizing Watershed Using Multivariate Elasticity”