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Al-Khwarizmi 

  Engineering  

Journal 
Al-Khwarizmi Engineering Journal,Vol. 13, No. 2, P.P. 100- 106 (2017) 

 

 

Design a Vegetative Filter Strips Length Using VFSMOD_W Model 

for Reducing Sediments and Pesticides 
 

Hayat Kareem Shukur*               Dawood E. Sachit** 
*Department of Civil Engineering/ Collage of Engineering / University of Al-Mustansiryah 

** Department of Environmental Engineering/ Collage of Engineering / University of Al-Mustansiryah 

*Email: hayat.azawi@okstate.edu 

**Email: dawood.sachit@okstate.edu 

 
(Received 4 October 2016; accepted 29 January 2017) 

https://doi.org/10.22153/kej.2017.01.005 

 

 

Abstract 

 
The vegetative filter strips (VFS) are a useful tool used for reducing the movement of sediment and pesticide in 

therivers. The filter strip’s soil can help in reducing the runoff volume by infiltration. However, the characteristics of 

VFS (i.e., length) are not recently identified depending on the estimation of VFS modeling performance. The aim of 

this research is to study these characteristics and determine acorrelation between filter strip length and percent 

reduction (trapping efficiency) for sediment, water, and pesticide. Two proposed pesticides (one has organic carbon 

sorption coefficient, Koc, of 147 L/kg which is more moveable than 100, and another one has a Koc of 2070 L/kg which 

is less moveable than 1000 are presented, where the goal is to prevent 95% of incoming sediment and 85% of the 

incoming pesticide to reach a receiving stream in still water, Oklahoma from a cultivated field (1250 m²),for 2 hour 

storm with 5 years return period. Several VFS lengths were simulated including1, 3, 5, 6, 9, 11, 12, and 13 m. The 

results showed that the percent of reduction of sediment, pesticide, and water mainly depends on VFS lengths. 

Moreover, considering the design storms range, the simulation illustrated that the optimal filter length was13m for 

silty clay loam. When the value of ���, was increased from 147 L/kg to 6070 L/kg, the filter length decreased from 13 
to 9.5 because of the increase in trapping efficiency. In addition, the results revealed that the trapping efficiency was 

for sediment but not for water orpesticide which was highly impacted by the narrow filter strips. The amount of the 

rainfall and runoff of the designated field was larger than the infiltration capacity of filter strips, which resulted in low 

trapping efficiency for pesticide and water. 

 

Keywords: Models ,runoff, sediment, vegetative filter strip, , water quality, watershed planning. 

 

1. Introduction 
 

Watershed planners were encouraged by the 

U.S Environmental protection agency (USEPA) 

to use a vegetative filter strip as a tool to control 

runoff quantity and quality [1] since the amount 

of surface runoff depends on the amount of rain 

and watershed characteristics such as soil type, 

land use, size, vegetation cover, soil moisture 

condition, and topography [2]. An effective way 

to minimize the amount of water and sediment 

and other contaminants in surface runoff from 

reaching a stream was needed [3].  

Such an effective way is the vegetative filter 

strip modeling system (VFSMOD-W) which is a 

computer model to study hydrology, sediment 

and pollutant through VFS. Three sub models 

were connected to the VFSMOD model to study 

the buffer performance on an event by event 

basis; a petrov- Galerkin finite element kinematic 

wave over land flow submodels, a modified 

Green- Ampt infiltration submodel and 

University of Kentucky sediment filtration model 

for grass area [4]. 

VFS is defined by Grismer [6] as a vegetative 

land that is planted on purpose to trap sediment 



Hayat Kareem Shukur                    Al-Khwarizmi Engineering Journal, Vol. 13, No. 2, P.P. 1- 12 (2017) 

 

101 

 

and pesticide from runoff water. The goal of VFS 

is to protect surface water in a number of ways; 

(1) they trap as much as 75 to 100 percent of 

water’s sediment by infiltrating the surface 

water; (2) they hold nutrients in runoff through 
adsorption to soil particles; (3) they increase 
degradation so that the pollutant become less 

toxic; (4) they prevent over 60% of certain 
pathogens form the runoff. When designing VFS, 

there are some factors that need to be taken into 

account such as slope, site preparation, soil 

conditioning, width, placement, maintenance, 

and monitoring. Slopes less than 5 percent are 

work in VFS, while slopes greater than 15 

percent is not recommended. Grismer [6] 

concluded that the width of filter strips is an 

important element affecting the performance of 

VFSs. As the strips width increases the amount 

of runoff and sediment also increases. 

The design of filter strips has been studied by 

many researchers and there is an agreement that 

the length of filter strips needed to obtain a 

certain level of trapping efficiency is highly 

variable [5]. Therefore, to effectively measure 

the length of VFS, it is necessary to study the 

relationship between the amount of sediment and 

pollutant that could be stopped and the length of 

filter strips. 

Dosskeyet al [3] evaluated a vegetative filter 

strip model to develop a design aid that is easy to 

use. Slope, soil texture, field length and field 

covers were used as variablesto determine the 

amount of sediment by using ten different 

combinations of lengths and widths. They 

reported that the narrow filter strips can be highly 

effective in some cases, while in others, even a 

small impact, could not be achieved at any 

practical width. In addition to that, it was found 

that as the slope increased or the texture of soil 

become finer, the trapping efficiency decreased 

and the field runoff increased as shown in Figure 

(1). Moreover, as field length or C factor (crop 

factor) increased the amount of runoff also 

increased, thus, the trapping efficiency of 

sediment become lower than that of shorter field 

with lower C factor (better condition).  

 

 
 

Fig. 1. Sediment trapping efficiency as a function 

of VFS width for two different sites having two 

different soil [3]. 

 
 

Dillahaet al [9]found that increasing VFS 

length will help to increase the trapping 

efficiency up to a certain level thereafter, any 

additional length does not make any 

improvement in filter performance. Furthermore, 

Holvoet et al [2]indicated that the best 

management practices can decrease the level of 

different pesticide input to a large extent but, 

more field study should be made in combination 

with modeling exercises in order to achieve good 

results whose measurements are most effective. 

Barfield et al [1], on the other hand, presented a 

steady state model to estimate the trapping 

efficiency of sediment in a filter strip under 

different variables. The trapping efficiency,��, of 
a filter strip can be calculated as follows [1]: 

�� � 	
��	

	
�                                                           …(1) 
Where ��� and ��� are incoming and outgoing 
sediment load per unit channel width. 

The aim of this research is to study the 

characteristics of VFS (i.e., length) and 

determine a correlation between filter strip length 

and percent reduction (trapping efficiency) for 

sediment, water, and pesticide. 
 

 

2. Materials and Method 
 

The vegetative filter strip modeling system 

(VFSMOD-W) version 5.x[4] was used to 
estimate the reduction of sediment, pesticide, and 

water by many different lengths of grass filter 

strip. A field site in Oklahoma was selected to 

monitor the performance of VFS. The design will 

receive water and sediment from a 50 m wide by 

25 m long source area. By using Table (1)with 

the soil- texture triangle of 17.1 % sand, 54.1 % 



Hayat Kareem Shukur                    Al-Khwarizmi Engineering Journal, Vol. 13, No. 2, P.P. 1- 12 (2017) 

 

102 

 

silt, and 28.9 % clay, the soil type was found to 

be silty clay loam type D[10]. For type D, 

cultivated area, and row cropscurve number is 

equal to 91 [9].  

Soil hydraulic parameters which are shown in 

Table (1) were taken from the United States 

Department of Agriculture (USDA) SSURGO 

database [9]. Default parameters of the VFS 

model were used and Bermuda grass type was 

assumed. The flow pattern of the source area is 

shown in Figure (2). 
 

Table 1, 

Input parameters for the VFSMOD-W[8,9]. 

Parameter Model Input Value 

Soil type Silt clay loam with 17.1% 

sand, 54.1% silt,and 

28.9% clay and 2.58% 

organic carbon. 

Soil hydraulic 

conductivity 

9.3 cm/hr 

Soil bulk density 1.44 �/��� 
Average section at the 

wetting front (SAV) 
0.43m 

Intial water content �� 0.17 
Slope 5.25 % 

Crop factor (C) 0.05 

Practice factor (P) 0.5 

Mediam parcticle size 

of incomin 

sediment ( ���) 
0.001 

 

Adsorption 

coefficient (��� ) 
147 L/kg -6070 L/kg 

 

 
 

Fig. 2. Case study characteristics (source area). 

 
 

The Porosity,(∅), which is the fraction of 
void space in the soil, is defined by the ratio: 

∅ �  !"!# � 1 −
&'() �*+,-./

012.-�(* �*+,-./ (2.65 ���3)
          …(2) 

Where6!is the volume of void space, and 67is 
the total or bulk volume of the materials [11]. 

VFSMOD required storm-based hourly rainfall 

data. In this study, the Natural Resource 

Conservation Soil method (NRCS) for 

calculating the rainfall excess was used for5-

year-2hr storm, Type ll curve [10]. The 

dimensionless precipitation,
89

8:;
, is the cumulative 

rainfall (<= )as function of time divided by the 
total 24-hour rainfall amount (<>?). The 24hr, 5-
year storm is equal to 5 inches[10]. The peak 

rainfall intensity occurs at the time when the 

slope of the cumulative rainfall distribution is the 

steepest, which for the NRCS 24-h hyetograph 

type II is from 11hrto 13 hr. The rainfall event 

was calculated to be 68 mm as shown in Table 

(2). 

 
Table 2, 

Rainfall depth calculations using NRCS method. 

Time, hr 
@A

@BC
 Depth, in 

11 0.235 0.0 

11.5 0.283 0.25 

12 0.663 1.9 

12.5 0.735 0.36 

13 0.772 0.18 

  
D B. EF GH 

= 68mm 

 

 

3. Design Guide Procedures 
 

One of the most important steps to develop a 

design guide for evaluating VFS performance is 

that the user must provide inflow hydrographs 

from the source area. Using the inputs of 

hyetograph in Figure (3) and the hydrograph in 

Figure (4), VFSMOD simulates the transport and 

deposition of sediment within the VFS. In the 

VFS model, the field length is defined as the 

distance from the edge of the field to the edge of 

the VFS as shown in Figure (2). VFS width 

which is the same as the field width is calculated 

by dividing the area of the field (1250 m²)by 

the field length. Several VFS lengths (1, 3, 5, 
6, 9, 11, and 13 m) were used in the simulation to 

estimate the reduction of sediment, runoff inflow, 

and pesticide as explained in Table (3). Then, the 

results were developed into graphical 

representation which are easier to understand 

than those of the tables as shown in Figure(5).In 

addition, to study the effect of the width of the 

filter strip on the trapping efficiency of the 

pesticide, the width was reduced to 90%, 75%, 

25%, 10% and 5% of the field width and applied 



Hayat Kareem Shukur                    Al-Khwarizmi Engineering Journal, Vol. 13, No. 2, P.P. 1- 12 (2017) 

 

103 

 

to the model. The percent reduction in the 

pesticide which were obtained from the 

VFSMOD simulation are listed in Table (4) and 

were developed into graphical representation as 

illustrated in Figure (6). 
 

 
 

Fig. 3. Hyetograph of the case study. 

 

 
 

Fig. 4.  Hydrograph of the case study using 

VFSMOD. 

 

Table 3, 

VFSMOD-W output file. 

VFS 

Length, m 

Source 

length, m 

Vegetation 

Type 
H,cm 

Sediment 

Reduction, % 

Runoff Inflow 

Reduction, % 

Pesticide 

Reduction, % 

1 24 Bermudagrass 1.35 74.187 10.19 35.018 

3 22 Bermudagrass 1.35 89.699 23.142 52.766 

5 20 Bermudagrass 1.35 94.174 32.056 62.36 

6 19 Bermudagrass 1.35 94.582 34.84 66.672 

8 17 Bermudagrass 1.35 96.514 40.289 71.67 

9 16 Bermudagrass 1.35 96.89 42.164 77 

11 14 Bermudagrass 1.35 97.8 56.294 78.6 

12 13 Bermudagrass 1.35 98 58.361 79.8 

13 12 Bermudagrass 1.35 99.47 60.149 89.889 

 

 

 
 

Fig. 5.  Percent reduction in sediments, pesticides, 

and runoff relative to vegetative filter strip (VFS) 

length (1, 3, 5, 6, 9, 11, 12, and 13 m) with organic 

carbon sorption coefficient, IJK of 147 L/kg. 
 

 

Table 4, 

Values of VFS width and trapping efficiency of 

pesticide. 

Width, m Trapping Efficiency % 

50.0 89.889 

45.0 89.115 

37.5 86.539 

25.0 79.566 

15.0 63.341 

5.0 41.756 

 
 

 

 

 

 

 

 

 

 



Hayat Kareem Shukur                Al-Khwarizmi Engineering Journal, Vol. 13, No. 2, P.P. 100- 106 (2017) 

 

104 

 

 
 

 
 

Fig. 6. Relationship between VFS widths and 

trapping efficiency of pesticide. 

 

 

4. Results and Discussion 
 

The simulation results clearly showed that 

increasing the filter strips length will help to 

increase the trapping efficiencies for sediment 

and pesticide as shown in Figure (5).The filter 

strip as narrow as 5 m was estimated to trap 

nearly 95% of the incoming sediment and only 

62% of incoming pesticide, while 13 m strips 

trapped 99.47% of incoming sediment and 89.9% 

of incoming pesticide(see Figure(5)). Thus, the 

relatively narrow filter strips can have great 

impact on the trapping efficiency for sediment 

but not for water or pesticide. 

The trapping efficiencies of a given length of 

filter strips also depend on the spacing of 

vegetation being planted and the kind of material 

being trapped.  High trapping efficiencies were 

estimated for sediment and much lower trapping 

efficiencies were estimated for water under the 

same conditions as displayed in Figure (5). The 

low trapping efficiencies for water illustrates that 

rainfall plus field runoff often greatly exceeds the 

infiltration capacity of filter strips. The filter 

length decreased from 13 to 9.5 when the value 

of ( ��� ) was increased from 147 L/kg to 6070 
L/kg because the trapping efficiencies of the 

sediment and pesticide increased as presented in 

Table (5). The VFS width also affected the 

trapping efficiency, as the width increases, the 

trapping efficiency also increases as shown in 

Figure (6). 

 

 

 

 

 
 

Table 5, 

Values of ILM and VFS 
Length, 

m 
 ILM 

Sediment 

Reduction, 

% 

Pesticide 

Reduction, 

% 

13 6070 99.47 94.692 

11 6070 90.310 90.616 

9 6070 97.244 84.238 

9.5 6070 97.385 85.088 

 
 

5. Conclusion 
 

Vegetation filter strips (VFS) are areas 

planted on purpose along streams, ponds, and 

lakes to remove sediment, organic materials, and 

chemicals carried in runoff or wastewater. The 

VFSMOD model is recommended to use by the 

U.S Environmental Protection Agency (USEPA) 

as a design aid to remove the amount of 

sediment, organic materials, and chemical carried 

in surface water. The results showed that the 

vegetative filter strips length is the most 

important parameter that directly affects the 

trapping efficiency.  Increasing the filter strips 

length will help to increase the trapping 

efficiency up to a certain level thereafter, any 

additional length does not make any 

improvement in filter performance.  

To prevent 85% of incoming pesticide to reach a 

receiving stream, it requires longer filter strips 

than sediment. The optimal filter length obtained 

was 13m. High trapping efficiencies were 

estimated for sediment and much lower trapping 

efficiencies were estimated for water under the 

same conditions. The low trapping efficiencies 

for water illustrates that rainfall plus field runoff 

often greatly exceeds the infiltration capacity of 

filter strips. When the value of adsorption 

coefficient (��� ) was increased from 147 L/kg to 
6070 L/kg, the filter length decreased from 13 m 

to 9.5 m because the trapping efficiencies for 

sediment and pesticide increased. 

The advantages of VFSMOD model over 

other models used to simulate VFS are the 

flexibility to change the parameters (slope, 

vegetation type, spacing of vegetation, etc.) 

along the filter and handling of complex storm 

pattern and intensity.  

Based on this study, it is recommended to 

implement vegetation filter strips in many 

regions in Iraq along the numerous streams 

where the prevalent areas are agricultural fields 

which are full of pesticides and fertilizers used 

by farmers. In addition, since the soil 

characteristics are important factors in the VFS 



Hayat Kareem Shukur                Al-Khwarizmi Engineering Journal, Vol. 13, No. 2, P.P. 100- 106 (2017) 

 

105 

 

performance, field studies including evaluation 

of the implemented VFS are recommended as 

well. 

 

 

6. References 
 
[1] Barfield, B.J., Tollner, E.W., Hayes, J.C., 

1979. Filtration of sediment by simulated 

vegetation I. Steady-state flow with 

homogeneous sediment. Transactions of 

ASAE 22 (5): 540–545. 

[2] Holvoet, K.M., Seuntjens, P., and 
Vanrolleghem, P.A., 2007. Monitoring and 

modeling pesticide fate in surface waters at 

the catchment scale. Ecological modeling, 

209:53-64. 

[3] Dosskey, M. G., Helmers, M. J., and 
Eisenhauer, D. E. 2008. A design aid for 

determining width of filter strips. Journal of 

soil and water conservation, 64 (4):232-241. 

[4] Munoz-Carpen, R., and Parsons, J. E., (2010). 
VFSMOD -W: Vegetative filter strips 

modeling system v.5.x.: University of Florida. 

http://abe.ufl.edu/carpena/vfsmod/. 

[5] Munoz-Carpen, R., Parsons, J. E., and 
Gilliam, W. J., (1999). Modeling hydrology 

and sediment transport in vegetation filter 

strips. Journal of hydrology, 214:111-129. 

[6] Grismer, E.M., 2006. Vegetative filter strips 
fot nonpoint source pollution control in 

agriculture. ANR publication 8195. California 

94608-1239. 

[7] Dillaha, T.A., Renea, R, B., Mostaghimi, S., 
Lee, D., 1989. Vegetative filter strips for 

agricultural nonpoint source pollution control. 

Transaction of ASAE 32 (2): 491-496. 

[8] United State Department of Agricultural 
(USDA). (2013). Web soil survey. Retrieved 

from 

<http://websoilsurvey.nrcs.usda.gov/app/Hom

ePage.htm> 

[9] United States Department of Agriculture 
(USDA), 2012. Geospatial data gateway. 

Retrieved from <datagateway.nrcs.usda.gov>. 

[10] Haan, C. T., Barfield, B. J., and Hayes, J. 
C., (1994). Design hydrology and 

sedimentology for small catchments. 

Academic press, INC., San Diego, 

California. 

[11] James, R., James, W., Finney, K., Nandana, 
P., Lucas, W., & Lee, M. (2012), Urban 

drainage modeling workbook (PCSWMM 

and SWMM5.0.002, Computational 

Hydraulic International(CHI). Canada. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



 )2017( 100-106 صفحة ،2العدد ،13المجلد الهندسية الخوارزمي جلةم                                  حياة كريم شكر                           

106 

 

 

 

  

  

للحد من الرواسب  موديل VFSMOD_W   استعمالبتصميم طول شريحة الغطاء النباتي 
  والمبيدات الحشرية

  

         **داود عيسى ساجت          حياة كريم شكر*    
  لجامعة المستنصريةا /الهندسة المدنية/ كلية الهندسة *قسم 

 لجامعة المستنصريةا /كلية الهندسة  /هندسة البيئة *قسم *
dawood.sachit@okstate.edu :البريد االلكتروني* 
hayat.azawi@okstate.edu :البريد االلكتروني** 

 

 

 
 الخالصة

 

  VFSـال و بحيرة . تصممامجرى مائي كنهر  إلى) هي أداة مفيدة تستخدم للحد من الرواسب والمبيدات الحشرية الداخلة VFSشرائح الغطاء النباتي (
 ، الخصائصمن جهة اخرى. طة عملية الترشيحسابوجم الجريان السطحي حقرب المجاري المائية وبموازاة خطوط جريان الماء فتساعد على خفض 

راسة هذه الخصائص وإيجاد .لهذا كان من الضروري دVFSكطول الشريحة مثال ليست حاليا محددة على أساس النمذجة التنبؤية ألداء الطبيعية  الفيزيائية
ولها ط مساحة متر ل ١٣وكذلك  ١٢، ١١، ٩، ٦، ٥، ٣، ١ عالقة بين طول الشريحة والنسب المئوية للرواسب والمبيدات المنخفضة. تم فحص عدة أطوال 

لفترة رجوع كل   ة عاصفة مطري٢ hrs تستقبل األمريكيةفي الواليات المتحدة  Stillwaterمتر لتربة طينية غرينية في مدينة  ٥٠عرضها  متر و ٢٥
اض نسبة انخف الحصول على قابلية حركة قليلة بهدف  يذ واآلخرقابلية حركة عالية  يفحص نوعين من الكربون العضوي ذ أيضا خمس سنوات . تم

ومقدار المبيدات المنخفضة  VFSمن الرواسب الواردة الى المجرى المائي. لوحظ وجود عالقة جيدة بين طول ال %٩٥ن المبيدات و م  %٨٥  مقدارها
  .لى نسبة الرواسب والمبيدات المنخفضة ع اً كبير اأثر VFS ـكما تبين ان لطول شريحة ال  اً متر ١٣لطول