The document compares three designs for saturated buffers to maximize nitrate load removal from agricultural drainage. Design 1 uses a fixed buffer width. Design 2 calculates an optimal width. Design 3, the newly proposed design, maximizes load removal over time by calculating optimal width and distribution pipe length. Results found Designs 2 and 3 consistently achieved maximum load removal across sites, unlike Design 1. Design 3 shows potential for use in decision tools by estimating load removal across a range of buffer widths. Future work will enhance Design 3 and link it to online tools for saturated buffer planning.

1. Yousef AbdalAal & Ehsan Ghane
Biosystems and Agricultural Engineering Department
Michigan State University
Comparative analysis of newly proposed and
existing design criteria for saturated buffers
11th International Drainage Symposium
IDS 2022
August 30 to September 2, 2022
Des Moines, Iowa

2. INTRODUCTION
2

3. Saturated Buffers
 Treat the field drainage that, originally, is released directly to the open ditch
Without
saturated
buffer
With
saturated
buffer
Reported nitrate load removal
8% 84%
A Need for a design criterion ensuring adequate & consistent performance
3

4. Study Objectives:
1. Propose a new design criterion for saturated buffer that maximizes the total nitrate load removal.
2. Conduct a comparative analysis of all SB design criteria to identify the criterion with most potential
to maximize the nitrate load removal.
4

5. METHODS
5

6. Saturated Buffers Design Criteria
8
Illinois NRCS
Spread Sheet
Design 1
Optimum Width
Eq. by McEachran
et al. (2020)
Design 2
Newly proposed design(builds on Designs 1 & 2 )
Design 3
3 meters 30 meters
NR1 NR2 NR3 NRn
W1 W2 W3 ………...
Optimum width is at Maximum nitrate load removal
NRn : Nitrate load removal
 One point in time
 Saturated buffer
parameters:
 Width : Input
 Distribution pipe
length : Output
 No optimization
 One point in time
 Saturated buffer
parameters:
 Width : Output
 Distribution pipe
length : No need
 Maximize
effectiveness of
nitrate load removal
 Time period of any length (Captures flow variations)
 Saturated buffer parameters:
 Width : Output
 Distribution pipe length : Input
Wn

7. Comparative Analysis of Design Criteria:
•Width: 9.1 m
•Calculated length of
distribution pipe (L)
Design
1
•Calculated optimum
Width
•Design 1 length of
distribution pipe (L)
Design
2
•Calculated optimum
Width
• Design 1 length of
distribution pipe (L)
Design
3
Designed
hypothetical SB
systems
Estimate nitrate load
reduction
Identify the
optimum
design
Largest
nitrate load
removal
Main routine of
comparative analysis
&
Measured daily field
drainage data
- Used measured daily data from two field sites in Michigan
9

8. Main Routine of Comparative Analysis and Design 3
10
Hydrology Component
Nitrate Load Estimation
Component
and

9.  Estimates diverted flow & Bypass flow
 Accounts for exit head loss
 Process based - Two mass balances :
First mass balance
Location: Control structure
Mass balance:
𝑄𝐹𝑖𝑒𝑙𝑑 = 𝑄𝑑𝑖𝑣𝑒𝑟𝑡𝑒𝑑 + 𝑄𝐵𝑦𝑝𝑎𝑠𝑠
Main Routine: Hydrology Component (1)
𝑸𝒅𝒊𝒗𝒆𝒓𝒕𝒆𝒅
𝑸𝑩𝒚𝒑𝒂𝒔𝒔
11

10. 𝐹𝑙𝑜𝑤 𝑡ℎ𝑟𝑜𝑢𝑔ℎ 𝑝𝑖𝑝𝑒
perforations
𝐹𝑙𝑜𝑤 𝑡ℎ𝑟𝑜𝑢𝑔ℎ buffer soil
Main Routine: Hydrology Component (2)
Exit head loss (h0 > h1)
Flow of water through perforations, same as subirrigation mode in (Skaggs, 1991)
Flow of water through the buffer soil to the open ditch, same as Design 1
Flow lines
Second mass balance - Location : Interface between distribution pipe & buffer soil
Mass balance :
𝐷𝑖𝑣𝑒𝑟𝑡𝑒𝑑 𝐹𝑙𝑜𝑤 = =
Flow lines
12

11. Main Routine: Nitrate Load Estimation Component
 First-order removal kinetics, same as Design 2
 Calculates the nitrate load from each flow component
Total Field load
Total load reaching ditch from SB
Load removal Total Field Load − Total Load reaching the open ditch from SB
=
13

12. RESULTS &
CONCLUSIONS
14

13. 0
10000
20000
30000
40000
50000
60000
70000
80000
90000
2 6 10 14 18 22 26
Total
Flow
volume
over
3-yrs
(m
3
)
Saturated buffer width (m)
Total diverted volume Total bypass volume
Design 3: Impact of Buffer Width on Flow Components
Buffer width can greatly impact the amount of diverted flow
15

14. Design 3: Impact of Buffer width on Load Components
0
50
100
150
200
250
300
0
200
400
600
800
1000
1200
1400
1600
2 6 10 14 18 22 26
Total
Nitrate
load
removed
by
SB
over
3-
years
(Kg-N)
Total
Nitrate
load
reaching
ditch
over
3
years
(kg-N)
Saturated Buffer (SB) width [m]
Total diverted flow load Total bypass load Total saturated buffer load Total Load removed by SB
Zero nitrate load from diverted flow
Maximum diverted flow
Maximum nitrate load removal by the SB

SB Design criteria should maximize nitrate load removal
16

15. Comparative Analysis of Design Criteria
CL site BL site
Design 1 Design 2 Design 3 Design 1 Design 2 Design 3
Buffer length (m) 433 643
Buffer width (m) 9.1 17.9 18.6 9.1 11.8 11.6
Total diverted flow (𝒎𝟑
)
71366
(36.1%)
45397
(23.0%)
44062
(22.3%)
25204
(28.3%)
21170
(23.7%)
21416
(24.0%)
Total nitrate-N load removed (kg)
258.4
(12.7%)
341.6
(16.8%)
342.0
(16.8%)
257.6
(17.2%)
266.8
(17.8%)
266.9
(17.8%)
Average annual diverted flow (𝒎𝟑
𝒚𝒆𝒂𝒓−𝟏
) 23879 15132 14687 8401 7057 7139
Average annual nitrate-N removed
(𝒌𝒈 𝒚𝒆𝒂𝒓−𝟏
)
86.2 113.86 114.0 85.9 88.9 89.0
Maximum diverted flow ≠ maximum nitrate load removal
Designs 2 & 3: Consistent maximum load removal regardless of site conditions
   

17

16. Design 3 Data Analysis & Potential
0
2
4
6
8
10
12
14
16
18
0
10
20
30
40
50
60
70
2 6 10 14 18 22 26 30 34
Percentage
nitrate
load
removal
(%)
Percentage
diverted
flow
(%)
Buffer width (m)
Diverted flow
Nitrate load removal
• Range of buffer width values with optimal nitrate load removal
• User-specified objective functions can be applied
• Estimated annual nitrate load removal can be used to give an estimate of nitrate credit values
Design
1
buffer
width
(9.1
m)
Buffer
width
at
98%
max
removal
(15.5
m)
Design
2
buffer
width
(17.8
m)
Design
3
buffer
width
(18.6
m)
Design 3 shows potential for use in SB decision-support tools
18

17. Future Work
 An online GIS tool linked to DRAINMOD to estimate daily drainage discharge
Required inputs to Design 3:
Further enhancement to Design 3:
 Incorporate more sophisticated hydrology and nitrate load estimation modules
20

18. Take-Home Messages:
 Increasing diverted flow to the buffer does not necessarily lead to more nitrate load removal.
 Designs 2 & 3 consistently provided maximum nitrate load removal regardless of sites
conditions, while this was not the case for Design 1.
 Design 3 has potential for use in decision-support tools related to SB.
21

19. Acknowledgements:
23

20. Email: Abdalaal@msu.edu
24