Transcript Document

Is the water table higher at flood sites than at nonflood sites? Yes (P=0.002)
Over the past 50 years, volume and timing of the Rio Grande’s flow, including the annual flood pulse,
have been altered due to damming and diversion of the river. As a result, the river is largely isolated
from its riparian forest, or bosque, and the native cottonwood forest is aging, is not regenerating, and is
being invaded by exotics. Restoration of native bosque may require restoring the annual flood pulse and
thus the hydrologic connection between the river and its floodplain. To determine the current extent of
hydrologic connectivity within a 160 km stretch of the Middle Rio Grande in New Mexico, we are
investigating the relationship among river flow, groundwater depth and soil moisture at 4 flood and 4
nonflood sites. United States Geological Survey station data are used to monitor river flow at various
locations within our study reach. Pressure transducers at each site measure groundwater depths
throughout the year. Water content of the top 30 cm of soil at each site is measured using a water
content reflectometer, and soil moisture from 25 to 100 cm below ground is measured using a neutron
probe. Preliminary analysis of pressure transducer data suggests that flood sites have a higher water
table than nonflood sites, and analyses of neutron probe data suggest that soil moisture is higher at flood
sites. In addition, soil moisture and depth to groundwater are negatively correlated. Results will help us
inform policy-makers on potential tools, such as managed seasonal flooding in years with adequate
water availability, to help restore the native bosque and the hydrologic connectivity between the river
and its floodplain.
Are groundwater levels at flood sites more responsive to river flow than
groundwater levels at nonflood sites? …Perhaps (to be investigated)
Depth to Water Table of All Sites (2001)
Belen (Flood) and Bernardo (Nonflood) Depth to Water Table
2001 Growing Season
40
Flood Sites
LL
80
-50
100
BLNB
120
BLN
140
BDAC
160
BDOC
SHK
AOP
Nonflood Sites
180
RGNC
200
Apr
May
Jun
Jul
Aug
Sep
Oct
2001
Introduction
Are soil moisture levels higher at flood sites than at nonflood sites? Yes
• The Rio Grande’s flows are about half of what they were 60 years ago, and half of the wetlands in
the Middle Rio Grande have been lost in just 50 years (Crawford et al. 1993).
• Without changes in water management, the Rio Grande bosque (riparian forest) will be dominated
by exotic species, namely salt cedar (Tamarix ramosissima) and Russian Olive (Elaeagnus
angustifolia) over the next 50 to 100 years (Howe and Knopf 1991).
• Restoration of native bosque along the hydrologically altered and highly controlled Rio Grande
would require instituting managed late spring/early summer floods in years with good water
availability that coincide with the historical peak in snowmelt discharge.
0.30
LL
Flood Sites
BDAC
BLN
BLNB
0.20
AOP
SHK
BDOC
0.15
Nonflood Sites
0.10
500
50
100
50
100
200
RGNC
0.05
1
Apr
LL
0.25
1000
150
0.35
0.35
Volumetric water content (mL/g soil)
• Cottonwood germination, which require sand bars and adequate moisture from high river flows
(Braatne et al. 1996), has declined substantially.
0
Soil Moisture 40 cm Below Ground (2001)
P=0.044
Soil Moisture 25 cm Below Ground (2001)
P=0.028
Volumetric water content (mL/g soil)
• Overbank flooding in late spring/early summer due to snowmelt runoff occurs in a very limited
area only in years with above-average snowfall. The last major floods in the Middle Rio Grande that
produced large-scale cottonwood establishment occurred in the springs of 1941 and 1942.
5000
Belen (flood site) center well
Bernardo (nonflood site) center well
Rio Grande flow (cfs) at Bernardo, NM
Depth to Water Table (cm)
Depth to Water Table (cm)
60
Rio Grande Discharge in Bernardo (cfs)
Abstract
May
Jun
Jul
0.30
Aug
Sep
Oct
Nov 1
2001
0.25
Flood Sites
BLNB
BDAC
0.20
What distinguishes flood sites from nonflood sites? Is it…
BLN
0.15
Elevation of wells in relation to the river?
BDOC
SHK
AOP
0.10
Distance of site to the river?
Nonflood Sites
0.05
Soil type, hydraulic conductivity, stratigraphy?
RGNC
0.00
0.00
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Apr
May
Jun
Jul
Aug
2001
Sep
Oct
Nov
Dec
2001
Are depth to groundwater and soil moisture correlated?
Yes, depth to groundwater and soil moisture are correlated at all depths
(i.e. 25, 40, 55, 70, 85 and 100 cm below ground).
Relationship Between Depth to Water Table
and Soil Moisture 100 cm Below Ground
Relationship Between Depth to Water Table
and Soil Moisture 40 cm Below Ground
0.35
0.5
Soil water content (mL/g soil)
Soil water content (mL/g soil)
LL
0.30
0.25
BDAC
BLNB
0.20
BDOC
BLN
SHK
AOP
0.15
R2 = 0.83
P = 0.002
0.10
Downloading pressure transducer
LL
0.4
BLNB
0.3
BDAC
BLN
BDOC
Groundwater well with
pressure transducer
SHK
AOP
0.2
R2 = 0.9
P=0
Literature Cited
0.1
RGNC
RGNC
0.05
60
80
100
120
140
160
180
200
0.0
60
80
100
120
140
160
180
200
Depth to water table (cm)
Depth to water table (cm)
Monsoon
rains
Flood pulse
0.28
0.24
1000
800
0.20
0.16
500
0.12
300
Apr
May
Jun
Jul
Aug
2001
Sep
Oct
Nov
Dec
Volumetric water content (mL/g soil)
2000
Acknowledgements
4000
3000
Rio Grande Discharge in Albuquerque (cfs)
Nonflood site with non-native understory of
salt cedar and Russian Olive, older
cottonwoods, and a large quantity of coarse
woody debris and litter on forest floor
Volumetric water content (mL/g soil)
0.32
Flood site with native understory of willow
and other species, relatively healthy
cottonwoods, and a small quantity of coarse
woody debris and litter on forest floor
0.32
4000
3000
Monsoon
rains
0.28
2000
0.24
1000
0.20
800
0.16
500
0.12
300
Apr
25 cm below ground
40 cm below ground
55 cm below ground
70 cm below ground
85 cm below ground
100 cm below ground
Rio Grande Discharge (cfs)
May
Jun
Jul
Aug
2001
Sep
Oct
Nov
Dec
Rio Grande Discharge in Albuquerque (cfs)
0.36
Howe, W.H., and F.L. Knopf. 1991. On the imminent decline of the Rio Grande cottonwoods in central New
Mexico. Southwestern Naturalist 36: 218-224.
Soil Moisture at Nonflood Sites (2001)
Soil Moisture at Flood Sites (2001)
Braatne, J.H., S.B. Rood and P.E. Heilman. 1996. Life history, ecology and conservation of riparian cottonwoods in
North America. In Biology of Populus and its Implications for Management and Conservation. Edited by R.F.
Stettler, H.D. Bradshaw, Jr., P.E. Heilman and T.M. Hinckley. NRC Research Press, Ottawa, Ontario,
Canada. pp. 57-85.
Crawford, C.S., A.S. Culley, R. Leutheuser, M.S. Sifuentes, L.H. White, and J.P. Wilber. 1993. Middle Rio Grande
Ecosystem: Bosque Biological Management Plan. U.S. Fish and Wildlife Service, District 2, Albuquerque,
New Mexico, 291 pp.
Is soil moisture at flood sites more responsive to river flow than soil
moisture at nonflood sites? … Perhaps (to be investigated)
Flood pulse
Taking soil moisture readings
with a neutron probe
UNM Hydrogeoecology Group
NSF Grant DEB-9903973
Middle Rio Grande Conservancy District
Bosque del Apache National Wildlife Refuge
City of Albuquerque Open Space Division
New Mexico State Land Office
Rio Grande Nature Center
Contacts
Jennifer F. Schuetz 505-277-5732
[email protected]
Jean-Luc Cartron 505-277-5732
[email protected]
Manuel C. Molles, Jr. 505-277-3050
[email protected]
Cliff N. Dahm 505-277-2850
[email protected]
Cliff S. Crawford 505-277-3411
[email protected]