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

24

Hui Shao (or Shawn)shaoh@uoguelph.caUniversity of Guelph

Thanks for your attention!

To be continued...