D.D. Bosch, J. Cho, G. Vellidis, R. Lowrance, T. Strickland

Little River Watershed Conservation Practice Assessment with SWAT

Outline Background Impacts of riparian forest buffer (RFB) Allocating Best Management Practices Results and Summary

Background

Little River Experimental Watershed in CEAP

•8 stream gages (334 km2)•Low slope, 2-3%•Dense stream network•41% row crop agriculture, 47% forest•Channels bordered by riparian forest

Little River Watershed

Objectives

Evaluate impacts of riparian forest buffers (RFBs) and conservation practices (crop and nutrient management)

Evaluate most effective approach for allocating Best Management Practices

Modeling procedure

Cause: landmanagement changes

Effects: Changes inHydrology and WQ

Calibration and Validation

Calibration on LRK Period: 1996-2004Rotation: Cotton-Cotton-

Peanut Validation on LRB without

changing parameters

334 km2

17 km2

Calibration and validation- LRK LRB for 1996-2004

CriteriaStreamflow (mm/yr) Sediment (ton/yr) TN (kg/yr) TP (kg/ha/yr)

Cal. Val. Cal. Val. Cal. Val. Cal. Val.Observed/Simulated 326/326 284/289 225/229 589/367 5615/6122 111237/82608 746/809 13393/7764

% error 0.0 1.7 1.5 -37.8 9.0 -25.7 8.6 -42.0Monthly NSE 0.94 0.89 0.43 -0.11 0.49 0.55 0.33 0.18

Streamflow

Total Nitrogen (TN) Total Phosphorus (TP)

0

50

100

150

200

250

300

1996 1997 1998 1999 2000 2001 2002 2003 2004

Mon

thly

sed

imen

t yie

ld (t

on) Observed

Simulated

0

50

100

150

200

1996 1997 1998 1999 2000 2001 2002 2003 2004

Mon

thly

str

eam

flow

(mm

) Observed

Simulated

sediment

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1996 1997 1998 1999 2000 2001 2002 2003 2004

Mon

thly

TN

yie

ld (k

g)

Observed

Simulated

0

200

400

600

800

1000

1200

1996 1997 1998 1999 2000 2001 2002 2003 2004

Mon

thly

TP

yiel

d (k

g)

Observed

Simulated

Cal

ibra

tion

14 m variable filter width for current conditions- width determined by current extent of buffer

14 m constant filter width for maximum conditions

Representing-No buffers-Existing buffer conditions-Maximum buffer conditions

Impacts of riparian forest buffer - Extent

Load Reductions due to Riparian Buffers - Extent

0

2

4

6

8

10

12

14

Se

dim

en

t L

oa

d (

ton

/h

a)

No R FB s C ur r ent

B uffer s

Maxi m um

B uffer s

0

20

40

60

80

100

120

Tota

l N

Loa

d (k

g/ha

)

N o RF Bs C u rre n tBu f f e rs

M a x i m u mBu f f e rs

0

2

4

6

8

10

12

14

16

Tota

l P L

oad

(kg/

ha)

No RF Bs Cur rentBuffers

Max i mumBuffers

Sediment Nitrogen Phosphorous

75 %

21 %

32 %76 %

Stream-order approach: starting from low stream order to high stream order, applied buffers to all un-buffered area

1st order > 2nd order > 3rd order > 4th order > 5th order72% 87% 95% 99% 100%

Impacts of riparian forest buffer - Location

0

5

10

15

20

25

1st 2nd 3rd 4th 5thStream order

Red

uctio

n ra

te (%

)

SedimentTotal nitrogenTotal phosphorus

0

1

2

3

4

5

1st 2nd 3rd 4th 5thStream order

Sed

imen

t loa

d fro

m H

RU

to s

tream

(ton

/ha)

Current RFBMaximum RFB

Impacts of riparian forest buffer - Location

Sediment Reduction rates

21.6 %

21.7 %

3.8 %1.0 %

0.1 %

Results - Buffers Maximizing buffer extent could be expected to produce

minor decreases in sediment (21%), total N (7%), and total P (20%) of the HRU load, less at watershed outlet

Greatest impacts on would be obtained by installing buffers on lower order streams, higher order streams already buffered

Greatest impact on sediment followed by phosphorous followed by nitrogen

BMP allocation approaches- Major Conservation Practices

Crop management practice (CMP) Contour farming, grassed waterway, terrace, and conservation

tillage, are grouped together

Nutrient management practice (NMP) 30 % decrease in nutrients applied

BMP allocation approaches

NMP

Stream-order approach: starting from low stream order to high stream order

Modeling approach: BMPs applied to critical areas based upon SWAT HRU output (Targeting)

Random approach: represents current allocating method16% 33% 50% 76% 83% 100%of remaining crop areas

36% 72% 87% 95% 99% 100%

16% 33% 50% 76% 83% 100%

1st order 2nd 3rd 4th 5th

Load Reductions due to Crop Management Practices - Extent

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Se

dim

en

t L

oa

d (

ton

/h

a)

Cur rent Max i mum0

10

20

30

40

50

60

70

80

Tota

l N

Loa

d (k

g/ha

)

Cur rent Max i umum0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Tota

l P L

oad

(kg/

ha)

Current Maximum

Sediment Nitrogen Phosphorous

55 %

0.6 %

56 %

Sediment Total phosphorus (TP)

Load Reductions due to Crop Management Practices – Extent and Location

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Se

dim

en

t L

oa

d (

ton

/h

a)

Cur rent Max i mum0

10

20

30

40

50

60

70

80

Tota

l N

Loa

d (k

g/ha

)

Cur rent Max i umum0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Tota

l P L

oad

(kg/

ha)

Current Maximum

Sediment Nitrogen Phosphorous

0.8 %10.3 %

4.3 %

Load Reductions due to Nutrient Management Practices - Extent

Total phosphorus (TP)Total nitrogen (TN)

Load Reductions due to Nutrient Management Practices – Extent and Location

Results – BMP allocation Comparison of implementing Riparian forest buffers RFB,

crop management plans (CMP), and nutrient management plans (NMP). Sediment: CMP > RFB > NMP Total nitrogen: NMP > RFB > CMP Total phosphorus: CMP > RFB > NMP

Impacts of spatial allocation approaches Targeting most critical areas showed the greatest reduction rates

Conclusions Model application indicates the greatest environmental gains

can be obtained through targeting critical areas Buffers should be installed / retained on all lower order

streams Greatest impact is expected through maintaining existing

buffer systems Substantial investment would be necessary to see incremental

changes in nutrient loading

Questions?