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 69 th SWCS International Annual Conference MAKING WAVES IN CONSERVATION
Terraces in crop fields are one of the most important soil and water conservation measures that affect runoff and erosion processes in a watershed. In this paper, terrace effects on soil erosion and sediment transport in the upstream and middle sections of the Weihe River basin in the Loess Plateau were analyzed using the newly developed terrace algorithm within the SWAT model. Monthly runoff and seasonal sediment yield data between 1960 and 1969 were used to calibrate and validate the model when only a small amount of terraces and reservoirs were installed. The model was then modified to represent terraces based on the survey data. Results indicated that, between 2000 and 2009, terraces in the watershed significantly decreased average annual sediment yields in the upstream and middle sections of the Weihe River by 28 million tons, which is about 10.6% of the sediment transported without terraces. Terraces were also estimated to have decreased sediment transport at the outlet of the watershed by 16.2 million tons per year. The unit area sediment reduction from terrace installation was 3000 t/km2. These effects were important for sediment transport and deposition control, and water quality improvement in the Weihe River basin of the Loess Plateau. Scientists, water resources managers and conservationists will benefit from this algorithm that provides a process-based tool for evaluating and optimizing terrace installation effects at watershed scale.
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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.