Transcript Sedimentology, Resource Conservation Methods and

Sedimentology, Resource Conservation
Methods and Environmental Policy of Irrigated
Row Crop Agriculture in the Salinas Valley, CA
Don Kozlowski
May 2001
Background
•1972, Clean Water Act, Sect. 303(d)
list & fix pollution via TMDL
•Salinas River listed as impacted by
sediment
•Beneficial uses & the Endangered
Species Act
•2001, still no TMDL for the Salinas
•Salinas Sediment Study hired by
state for technical assistance
Possible Sources
•Urban/suburban
•Grazing
•Viticulture
•Natural processes
•Recreational use
•Mining
•Agriculture
•15% of area is row crop agriculture (165,000 ha)
•40% sediment of U.S. rivers from cultivated land
•ag’s contribution to the Salinas River?
Objectives
Determine:
• Typical sediment yields from row crop ag fields due to
irrigation and storm events during a season
• Efficiency of a particular best management practice, the
water/sediment detention basin
Methods
Site selection
Filtration
Catchment construction
Recording and analysis
Methods (cont’)
• Create model that predicts field erosion
– Determined from various event parameters
• Upscale the field data to watershed scale
– GIS model to get area & slope
– Rainfall model
• For detention basins
– Compare sediment into basin to sediment out
Results
(15 events monitored: 9 irrigation, 6 rainfall)
Erosion Analysis (example):
Total soil off field: 2.8 tonnes
Erosion per area: .547 tonnes/ha
50
900
45
750
40
35
600
30
25
450
20
300
15
10
150
5
0
2:00
0
3:00
4:00
Rain
5:00
Runoff
6:00
7:00
TS Conc.
Load
8:00
9:00
Sediment Load (g/sec)
Rain (mm/hr), Runoff (L/sec) Rates,
TS Concentration (g/L)
I010219-E (5.1 ha)
2/19/01 Rain Event
Results (cont’)
Erosion Model:
Log Erosion vs Modeled Log Erosion
0
log E = 0.89 x log M + log A + 0.64 x S – 4.1
Modeled Log Erosion
-0.5
-1
E = Erosion (tonnes/ha)
M = Maximum intensity of rainfall/applied water
A = total Amount of water fallen/applied (mm)
S = Slope of the field (% )
-1.5
-2
-2.5
-3.000
-2.500
-2.000
-1.500
Log Erosion
-1.000
-0.500
0.000
Still More Results
• Watershed Scale Erosion Estimates:
– Rainfall:
93 kilo-tonnes, 1.2 tonnes/ha
– Irrigation: 141 kilo-tonnes, 1.7 tonnes/ha
– Total:
234 kilo-tonnes, 2.9 tonnes/ha
CAUTION!!
– 60% of agricultural row cropland, slopes <2.3%
– Only a fraction of this made it to the Salinas River
•
Efficiency of Detention Basin
– 100% for sand, at least 99% for silt/clay
– 211mg/L max outgoing; 46,400 mg/L max
incoming
Discussion/Wrap-up
• Agricultural land use produces a lot of erosion
• Many BMP’s are in place
• Detention basins appear to work well
• Improvements:
– Storm erosion dynamics, need more data
– Slopes > 2%, need data
– Rain model
Acknowledgements
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Farmers
SSS team (Thor, Wendi, Adrian, Alana, Bronwyn, Joel, Julie)
Mark Angelo, RWQCB
Bryan Largay, Monterey Co. RCD
NASA/EPA
Dr. Sharon Anderson
Dr. Lars Pierce
Dr. Fred Watson