Download - Terrace effects on soil erosion processes
Model Development
Watershed modelling
Terrace evaluation
Future research
Terrace Effects on Flow and Soil Erosion
Processes in a Watershed of
the Loess Plateau
Hui Shao (Shawn) PhD
Dept. of Geography
University of Guelph
JULY 2014
69th SWCS International Annual Conference
MAKING WAVES IN CONSERVATION
Terrace model2
Introduction1
Terrace evaluation4
Watershed simulation3
Content
Conclusions & Future5
Introduction
Part 1 1.1 What is terrace?
Purposes & Benefits
Increase infiltration and soil moisture
Reduces soil erosion
Improves water quality by reducing
sedimentation
Controls runoff peak flow
Terrace practices are one of the oldest
and most widely used means of saving
water and controlling erosion all over
the world.
Normal terrace
Bench terrace
3
Introduction
Part 1
Serious erosionFlood & river pollution etc.
1.2 Background
Environmental issues of the Loess Plateau
Yellow riverBank
River bed 13m
Sediment deposition
Ground Deposited volume(108 m3)
Scientific• Terrace overland
effects• Watershed impacts
Technical• Conceptualize
different terrace type
• Terrace algorithms
• Incorporation to hydrological model
• Easy to use
Conservation measures
Terraces
Check damsForestation
1.3 Scientific questions
Weihe river
Yellow reiver
Challenges of evaluate terraces effects
Check damsForestation
Conservation tillage Terraces
√ √
√
?
Introduction
Part 1
Process-based terrace simulation
2.1 Concept designTerrace model
Part 2
Process-based terrace algorithm in HRU
H. Shao, C. Baffaut, J. E. Gao et al. 2013. Development and Application of Algorithms for Simulating Terraces within SWAT. Transaction of ASABE, 56(5): 1715-1730.
Parameter Represent effects
CN2 Adjust rainfall infiltration in terrace
USLE-P Reduce sediment losses
SLSUBBSN Distance between terraces
Traditional terrace modelling method(Parameter representation)
Waidler, D. et al. 2011. Conservation Practice Modeling Guide for SWAT and APEX. TR-399. College Station, Texas A&M University System.
Lu
(Undisturbed)
Lterrace (Terrace unit)
α0
Soil layer 2 ……
Soil layer 1
Cut Fill
Cut Fill
Lb
(Bed or Frontslope)
Lr
(Riser or Cutslope)
Lr
(Riser or Cutslope)
Lb
(Bed or Frontslope)
Lr
(Riser or Cutslope)
Lr
(Riser or Cutslope)
Terrace types and segments01
2.2 Terrace algorithm
Runoff: SCS curve number
Erosion: MUSLE method
Nutrients: nitrogen & phosphorous
Plant growth: optimal growth & stress
More: plant management, lateral flow,
water harvesting etc.
Map of normal terrace
Map of bench terrace
Terrace model
Part 2
Sub-daily simulation
Sediment and nutrient settlement
Extra infiltration
Extra evaporation
Inside terrace channel erosion
Terrace outputMap of normal terrace
Terrace storage effects02
2.2 Terrace algorithmTerrace model
Part 2
Generate standard input files
Batch modifications
Read original SWAT parameters
Modify parameters (e.g. CN2) based on terrace shapes
Subbasin list
Terrace fraction
Inflow fraction
Read variable values from original SWAT
input filesCreate terrace input files
Write, modify or delete terrace related variable values
Terrace input control and sample files
Control code
Compiling environment
Features of TIA
2.3 Terrace input assist tool (TIA)Terrace model
Part 2
Framework of the Terrace Input Creation and Modification Tool
10
The Wei River is the largest branch of the Yellow River and locates in the south end of the Loess Plateau.
Wei River
Yellow River
Study area – the Wei River basin
3.1 The Wei River basinWatershed simulation
Part 3
• Area: 134,800 km2
• Land use: Agriculture (45%), grass (38%), forest (15%), others (2%)
• Erosion rate: 3000 ton/(km2*year)• Average precipitation: 572 mm
Input data and watershed division
3.2 SWAT model setupWatershed simulation
Part 3
26 weather stations (left figure)、 103 soils、25 land use types
The main river basin was divided into 4
calibration areas by 4 hydrological stations
Weather stations used in Wei River basin Calibration areas of the basin
718 subbasins with average area of 187km2
Weather stations distributions
Shaanxi Prov.
Gansu Prov.
Ningxia Prov.
Flow simulation (Validation 1965-169)01
0
2000
4000
6000
8000
10000
实测值 模拟值
Dai
ly fl
ow (m
3/s)
Daily flow of Huaxian station
Station Mon NS Annual r2 PBIAS NS criteria r2 criteria PBIAS criteria
Linjiacun 0.75 0.94 0%
0.50 0.80 ±25%Weijiabao 0.78 1 -16%
Xianyang 0.81 0.95 -6%
Huaxian 0.47 0.81 -7%
Measured Simulated
3.3 Calibration & validation resultWatershed simulation
Part 3
Sediment simulation (Validation 1965-169)02
Station Seasonal NS Annual r2 PBIAS NS criteria r2 criteria PBIAS criteria
Linjiacun -0.01 0.48 -4%
0.60 0.80 ±50%Weijiabao -0.28 0.83 -61%
Xianyang 0.78 0.89 -2%
Huaxian 0.93 0.94 3%
1960/1 1961/1 1962/1 1963/1 1964/1 1965/1 1966/1 1967/1 1968/1 1969/10
15000
30000
45000
60000
75000
90000 实测值 模拟值
Sed
imen
t (10
4·t)
Monthly sediment of Huaxian station
0.0
1.0
100.0
10000.0
1000000.0
月泥沙对比
Measured sediment (104·t)
Sim
ula
ted s
edim
ent
(104·t
)
Monthly sediment of Huaxian station
Measured Simulated Sediment comparisonline
Watershed simulation
Part 3 3.3 Calibration & validation result
Terrace evaluation
Part 4
Study area – main river of the basin01
4.1 Evaluation method
Terrace fraction in 2000 was 15.2% at the up stream of the basin
Terrace fraction = 6.4% at the middle stream
3.0% of terrace at down stream
15
0
10
20
30
40
50
60
70
80上游
中游
下游
Terrace scenario
Te
rra
ce
fra
cti
on
(%
)
Scenario design:
8 terrace scenarios were designed based
on measured data (bottom figure) with
average distribution.
Terrace parameters:
All terraces were set as bench terrace with
ridge height of 30cm. All in terrace parameters
came from the calibrated HRU values.
Up stream
Mid stream
Down stream
Terrace evaluation
Part 4
Terrace scenarios02
4.1 Evaluation method
16Surface runoff Lateral flow Base flow
Terrace evaluation
Part 4
Flow response01
4.2 Hydrological response to terrace
10
15
20
25
30
35Surface Lateral Baseflow
Terrace scenarios
Wa
ter
yie
ld (
10
8·m
3/a
)
Surface, lateral & base flow:
Surface, lateral and base flow has changed
by -6.7%, +1.0% and +3.4% under S2000
terrace scenario compare to no terrace.
Total water yield:
Total water yield decreased -0.47% under
S2000 terrace scenario, and -2.7% under
S2000X5 terrace scenario.
Terrace evaluation
Part 4
Analysis of flow response02
4.2 Hydrological response to terrace
1 2 3 4 5 6 7 8 9 10 11 120
40
80
120
160
200
240 无梯田 No terrace S2000 梯田情景
Month
Str
ea
m fl
ow
(m
3/s
)
Stream flow of different terrace scenarios at Linjiacun station
Decrease peak value in flood
season
Increase base flow in dry season
No terrace S2000 S2000X5
Terrace evaluation
Part 4
Stream flow response
4.3 River flow response to terrace
Erosion was decreased by 10.6% under S2000 terrace scenario in
the upstream of Xianyang
Erosion was decreased by 65.3% under S2000X5 terrace scenario in
the upstream of Xianyang
Terrace evaluation
Part 4
Erosion response
4.4 Erosion response to terrace
ScenarioAnnul. Sed.
Load(106·t)
Change per terrace(t/ha)
ScenarioAnnul. Sed.
Load(106·t)
Change per terrace(t/ha)
No terrace 153.20 (100%) - S2000X2 119.20
(77.8%) -30.0
S1979 148.50(96.9%) -21.7 S2000X3 102.70
(67.0%) -29.7
S1989 144.30(94.2%) -26.3 S2000X4 86.75
(56.6%) -29.3
S2000 137.00(89.4%) -28.6 S2000X5 68.39
(44.6%) -29.9
Terrace evaluation
Part 4
Sediment load in the stream01
4.5 Sediment load and riverbed deformation
Upstream riverbed deposition was decreased by 2,180t/km under S2000
Riverbed can be prevented from lifting 3.9mm under S2000
Deposition has been decreased by 101 million tons (91mm of lifting) during 1970-2009
Middle stream riverbed deposition was decreased by
2,800t/km under S2000
Riverbed can be prevented from lifting 10.9mm under S2000
Deposition has been decreased by 66 million tons
(218mm of lifting) during 1970-2009
Terrace evaluation
Part 4
Riverbed deformation analysis02
4.5 Sediment load and riverbed deformation
Terraces significantly decreased surface runoff and sediment yields in the
Wei River basin, and affect the timing of the river stream.
Terraces were also estimated to have decreased sediment transport at the
outlet of the watershed by 16.2 million tons per year from 1970 to 2009.
The unit area sediment reduction from terrace installation was 30 t/ha.
Terrace effects were important for sediment transport and deposition
control, and water quality improvement in the Wei River basin of the
Loess Plateau.
Conclusions& Future
Part 5 5.1 Research conclusions
Conclusions& Future
Part 5 5.2 Future research
Informatio
nPart 1
SWAT input reading
tools, e.g. ArcSWAT,
AVSWAT.
Input conversion
tools
Watershed evaluation of BMPs in SWAT
ScenarioPart 2
ModelPart 3
DisplayPart 4
BMPs customer list
Multiple BMPs
Field level
Scenarios
comparison
SWAT model
Economic model
Integrated (cost-
effective) model
Database functions
SWAT output
Economic output
Integrated (cost-
effective) output
Live view output