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transcript
International Journal of Environmental Research and Development.
ISSN 2249-3131 Volume 7, Number 1 (2017), pp. 29-44
© Research India Publications
http://www.ripublication.com
A Study on Infiltration Characteristics of Soils at
Andhra University Campus, Visakhapatnam
Sreejani TP1, Abhishek D2, Srinivasa Rao GVR3, Abbulu Y3
JRF, Dept. of Civil Engineering, Andhra University
M.Tech Student, Dept. of Civil Engineering, Andhra University
Professor, Dept. of Civil Engineering, Andhra University
Abstract
An attempt has been made in the present work to evaluate infiltration
characteristics of soils at Andhra University campus using a single and double
ring infiltrometer. Experimentation work is carried out at five different points
in the campus. The study is aimed at determining the constant infiltration rates
of those soils using both the infiltrometers and comparing it with the
infiltration rates obtained by Kostiakov, Philip’s, and Horton’s and Green-
Ampt infiltration models. The values of various constants of the models are
calculated by graphical approach. To get best fitting model for a particular soil
condition the results obtained from various infiltration models are compared
with observed field data and graphs are drawn with correlation coefficient and
standard error as tools. The results showed that infiltration rate is as high as
17.43 cm/h near Samatha Hostel and, the infiltration is rate as low as 1.46
cm/h at Assembly hall area.
Introduction
Water in excess of infiltration capacity of the soil will flow overland as surface run-
off once the minor undulations in the surface have been filled. Runoff occurs most
frequently on degraded soils depending on topography and rainfall intensity. (Eze
Bassey Eze3 et.al 2011) Water is driven into the porous soil by force of gravity and
capillary attraction.( Jagdale5 et.al 2012). Infiltration is the process flow of water into
the soil profile vertically through the soil surface. Infiltration is crucial in modeling of
surface runoff, and it is usually difficult to be evaluated or measured accurately.
(Ieke4 et.al 2013) Infiltration capacity varies in space and time due to soil
heterogeneities, meteorological characteristics, clogging processes and temperature
fluctuations, as well as other processes. (Balraj Singh2 et.al 2014) The Infiltration
process is governed by two major factors viz. gravity which is a natural phenomenon
30 Sreejani TP et,al
and capillary action which is the ability of liquid to flow in narrow spaces (Anjaneya
Prasad1 et.al 2015). The methods used for calculation of infiltration capacity are
Green Ampt Method, General hydraulic budget method, darcy’s law, horton’s
equation. (Shikha6 et.al 2015). In the present study, the constant infiltration rates of
different soils under different soil conditions are calculated by double ring
infiltrometer method, and compared with the calculated values from Horton’s,
Philip’s, Kostiakov’s and Green-Ampt infiltration models. Also, the assessment of the
suitability of different models for estimation of infiltration rate of particular soil under
particular soil condition was carried out with correlation coefficient and standard error
as a tools.
Study Area
The study area, Andhra University is located in Visakhapatnam, Andhra Pradesh. It
lies between latitude 17º43’5.38’’N and longitude 83º19’17.61’’E with an area of 460
acres and a varying elevation from 10 MSL to 62.5 MSL. The average annual rainfall
is 1050 mm and the mean annual temperature and humidity are 23.7ºC and 67 to 78%
respectively. The study area is divided into two campuses viz., South campus and
North campus. Five locations are selected in the University each one at NCC building,
Near CSE Department, Samatha Hostel in the North Campus, as well as Dispensary
and Assembly hall in the south campus.
Figure 1: Study Area - Andhra University Campus
A Study on Infiltration Characteristics of Soils at Andhra University … 31
Materials and Methods
Measurement of Infiltration Rates:
Double ring infiltrometer method is used for measurement of infiltration rates at all
the sites. In this two concentric rings were used with 25cm deep, and diameter of
30cm for inner ring and 60cm for outer ring. The rings were driven at about 15cm
deep in soil by using falling weight type hammer striking on a wooden plank placed
on top of ring uniformly without undue disturbance to soil surface. Inner ring is
driven first. Water was poured into the rings to maintain depth of 5 to 9 cm and the
observations were carried out in the inner ring with measuring scale and stop watch.
Readings were taken at regular time interval of 2, 5, 10, 15, 30, 60 min. till getting a
constant infiltration rate.
The experimental setup consists of:
Two rings having diameter 30cm and 60 cm respectively of height 25cm.
One ring having diameter 30cm and height 60cm.
A wooden log having 4 cm x 4 cm and 70 cm in length.
A hammer.
A spade to collect the remove the sample from site.
A measuring scale having 30 cm in length.
Stopwatch.
Equipment for writing records.
Sufficient amount of water for reading.
Infiltration Models
The following infiltration models are considered for finding best fitting model to
observed field infiltration rate data.
Horton’s Equation (1933) Horton expressed the decay of infiltration capacity with
time as an exponential decay given by
fp = fc + (f0 – fc) e–kht for 0 ≥ t ≤ tc ---- Eq 1
Where,
fp = infiltration capacity at any time t from the start of the rainfall.
f0= initial infiltration capacity when t = 0
fc = final steady state infiltration capacity occurring at t = tc. Also, fc is sometimes
known as constant rate or ultimate infiltration capacity.
Kh= Horton’s decay coefficient which depends upon soil characteristics and
32 Sreejani TP et,al
Vegetation cover.
The difficulty of determining the variation of the three parameters f0, fc and Kh with
soil characteristics and antecedent moisture conditions preclude the general use of
Horton’s equation.
Philip’s Equation(1957) Philip’s two term model relates Fp (t) as
KtstFp 2/1
---- Eq 2
Where s = a function of soil suction potential and called as sorptivity.
K = Darcy’s hydraulic Conductivity.
Fp = Cumulative infiltration capacity
From the above equation infiltration capacity could be expressed as
Kstfp 2/1
2
1
---- Eq 3
3. Kostiakov Equation (1932) Kostiakov model expresses cumulative infiltration
capacity as
Fp= atb ---- Eq 4
Where,
Fp is Cumulative infiltration capacity
a and b are local parameters with a > 0 and 0 < b< 1.
The infiltration capacity would now be expressed as
fp= (ab) t(b-1) --- Eq 5
4. Green – Ampt Equation (1911) Green and Ampt proposed a model for infiltration
capacity based on Darcy’s law as
𝑓𝑝 = 𝐾 (1 + (𝜂𝑆𝑐/Fp)) ---- Eq 6
Where 𝜂 = Porosity of the soil.
Sc= Capillary suction at the wetting front and
K = Darcy’s Hydraulic Conductivity.
The above equation can be considered as, fp= m + (n/Fp)
Where m and n are Green – Ampt parameters of infiltration model.
A Study on Infiltration Characteristics of Soils at Andhra University … 33
Results and Discussion
The measured infiltration rates of soils in the field at five different locations in the
Andhra University are shown in table 1.
Table 1: Infiltration Rates (cm/hr) (Experimental Results)
TIME (Min) NCC
Building
CSE
DEPT.
SAMATHA
HOSTEL
DISPENSERY ASSEMBLY
HALL
2 25.2 9 109.2 23.1 6.22
4 18.3 8.7 90.84 22.5 5.21
6 9.9 8.4 87.3 19.8 4.57
8 8.4 8.1 76.5 18.3 4.16
10 7.8 7.8 74.64 16.02 3.96
15 6.84 6.72 71.04 15.9 2.92
20 5.64 6.36 65.4 15.72 2.74
25 4.92 6.12 65.2 15.6 2.46
30 4.68 6 60.36 15.34 2.43
35 4.2 5.64 58.68 15.04 2.25
40 4.08 5.6 56.52 14.7 2.12
50 3.96 4.8 54.72 14.64 1.7
60 3.6 4.4 54.6 14.4 1.46
70 3.42 3.8 53.28 12.64 1.46
85 3.32 2.72 50.52 12.32 -
100 2.96 2.69 46.58 11.88 -
115 2.84 2.6 41.92 11.32 -
130 2.8 2.36 37.26 10.92 -
145 2.68 2.24 33.48 10.32 -
160 2.68 2.2 30.17 9.72 -
190 - 2.06 26.98 8.76 -
220 - 2.06 22.72 7.8 -
250 - - 19.46 7.8 -
310 - - 17.43 - -
34 Sreejani TP et,al
370 - - 17.43 - -
Constant
Infiltration
Rate
2.68
2.06
17.43
7.8
1.46
Table 2: Parametric values of different infiltration models.
PLACE
HORTON’S
MODEL
fp=fc+(f0-
fc)e-k
ht
GREEN-
AMPT
MODEL
fp=m + n/Fp
KOSTIAKOV’S
MODEL
fp=(ab).t(b-1)
PHILIP’S
MODEL
fp=(1/2)s.t-1/2 +
K
K m n A b s K
NCC
building
2.0665 0.017 21.009 6.228 0.533 8.7724 1.0941
CSE
Department
1.4909 3.8246 2.3532 5.394 0.7784 3.4018 2.2873
Samatha
Hostel
0.7061 39.813 327.16 60.322 0.7859 35.798 26.658
Dispensary 0.6934 11.857 11.804 15.222 0.8548 6.158 9.3186
Assembly
Hall
3.2287 1.7384 1.1268 2.723 0.7186 2.212 0.7526
Table 3: Experimental Vs Calculated infiltration rates at NCC Building
Time (min)
Infiltration rate (cm/hr)
Experimental
value
Horton’s
model
Green-
Ampt
model
Kostiakov
model
Philip’s
model
2 25.2 23.7 25.03 30.6 25.14
4 18.3 22.3 14.51 13.5 18.1
6 9.9 21 11.82 10.8 14.97
8 8.4 19.77 10.22 9 13.11
10 7.8 18.64 9.07 8.1 11.85
15 6.84 16.11 7.29 6.84 9.87
20 5.64 14 6.26 5.88 8.69
25 4.92 12.2 5.58 5.28 7.89
30 4.68 10.7 5.06 4.8 7.3
35 4.2 9.43 4.67 4.44 6.84
A Study on Infiltration Characteristics of Soils at Andhra University … 35
40 4.08 8.36 4.34 4.2 6.47
50 3.96 6.7 3.83 3.78 5.9
60 3.6 5.53 3.46 3.48 5.48
70 3.42 4.7 3.16 3.18 5.16
85 3.32 3.88 2.81 2.96 4.78
100 2.96 3.4 2.56 2.72 4.49
115 2.84 3.11 2.36 2.52 4.26
130 2.8 2.94 2.19 2.32 4.08
145 2.68 2.83 2.05 2.24 3.91
160 2.68 2.77 1.93 2 3.78
Correlation
Coefficient
-
0.96
0.98
0.99
0.97
Standard
Error
-
2.0
1.09
0.89
1.32
Figure 2: Variation of experimental and calculated infiltration rates at NCC building
0
5
10
15
20
25
30
35
0 50 100 150 200Infi
ltra
tion R
ate
(cm
/hr)
Time, t (minutes)
Observed Infiltration rate (cm/hr)
Infiltration rate by Horton’s model (cm/hr)
Infiltration rate by Green-Ampt model (cm/hr)
Infiltration rate by Kostiakov model (cm/hr)
Infiltration rate by Philip’s model (cm/hr)
36 Sreejani TP et,al
Table 4: Experimental Vs Calculated infiltration rates at CSE Department-AU
Time
(min)
Infiltration rate (cm/hr)
Experimental
value
Horton’s
model
Green-
Ampt
model
Kostiakov
model
Philip’s
model
2 9 8.66 11.66 11.4 11.6
4 8.7 8.34 7.81 8.1 8.87
6 8.4 8.04 6.53 7.2 7.67
8 8.1 7.75 5.9 6.9 6.95
10 7.8 7.47 5.51 6.6 6.45
15 6.72 6.84 5.03 5.88 5.69
20 6.36 6.28 4.77 5.52 5.23
25 6.12 5.78 4.61 5.28 4.92
30 6 5.35 4.5 5.04 4.69
35 5.64 4.97 4.42 4.8 4.51
40 5.6 4.63 4.36 4.56 4.37
50 4.8 4.06 4.27 4.5 4.15
60 4.4 3.62 4.22 4.32 4
70 3.8 3.28 4.18 4.08 3.86
85 2.72 2.89 4.14 3.96 3.72
100 2.69 2.64 4.12 3.84 3.6
115 2.6 2.46 4.09 3.68 3.52
130 2.36 2.33 4.08 3.56 3.44
145 2.24 2.24 4.06 3.48 3.38
160 2.2 2.19 4.05 3.4 3.33
190 2.06 2.12 4.03 3.32 3.24
220 2.06 2.08 4.01 3.2 3.18
Correlation
Coefficient
-
0.99
0.73
0.99
0.88
Standard
Error
-
0.32
1.17
0.27
0.98
A Study on Infiltration Characteristics of Soils at Andhra University … 37
Figure 3: Variation of experimental and calculated infiltration rates at CSE
Department-AU
Table 5: Experimental Vs Calculated infiltration rates at Samatha Hostel-AU
Time
(min)
Infiltration rate (cm/hr)
Experimental
value
Horton’s
model
Green-
Ampt
model
Kostiakov
model
Philip’s
model
2 109.2 107.7 129.69 124.8 124.7
4 90.84 104.98 88.86 90.3 95.98
6 87.3 102.94 73.96 81 83.26
8 76.5 100.95 66.78 75 75.67
10 74.64 99 62.19 71.4 70.5
15 71.04 94.35 55.74 66.36 62.45
20 65.4 89.95 52.4 61.8 57.66
25 65.2 85.81 50.23 58.56 54.38
30 60.36 81.9 48.78 56.04 51.97
0
5
10
15
20
25
30
35
0 50 100 150 200
Infi
ltra
tion R
ate
(cm
/hr)
Time, t (minutes)
Observed Infiltration rate (cm/hr)Infiltration rate by Horton’s model (cm/hr)Infiltration rate by Green-Ampt model (cm/hr)Infiltration rate by Kostiakov model (cm/hr)Infiltration rate by Philip’s model (cm/hr)
38 Sreejani TP et,al
35 58.68 78.22 47.73 54 50.09
40 56.52 74.74 46.92 52.44 48.58
50 54.72 68.38 45.74 50.46 46.26
60 54.6 62.73 44.9 48.36 44.55
70 53.28 57.7 44.29 46.62 43.23
85 50.52 51.18 43.63 44.88 41.7
100 46.58 45.7 43.17 43.24 40.52
115 41.92 41.15 42.84 41.88 39.58
130 37.26 37.3 42.6 40.68 38.82
145 33.48 34.1 42.42 39.72 38.17
160 30.17 31.3 42.27 38.84 37.62
190 26.98 27.24 42.04 37.72 36.71
220 22.72 24.32 41.88 36.46 36
250 19.46 22.27 41.76 35.42 35.42
310 17.43 19.82 41.58 34.1 34.53
370 17.43 18.6 41.43 32.73 33.86
Correlation
Coefficient
-
0.97
0.82
0.99
0.91
Standard
Error
-
7.33
11.11
2.94
9
A Study on Infiltration Characteristics of Soils at Andhra University … 39
Figure 4: Variation of experimental and calculated infiltration rates at Samatha
Hostel-AU
Table 6: Experimental Vs Calculated infiltration rates at Dispensary-AU
Time
(min)
Infiltration rate (cm/hr)
Experiment
al value
Horton’
s model
Green-
Ampt
model
Kostiak
ov
model
Philip’s
model
2 23.1 22.75 27.18 24.9 26.18
4 22.5 22.41 19.62 24.1 21.24
6 19.8 22.07 17.27 18.9 19.05
8 18.3 21.74 16.08 17.4 17.75
10 16.02 21.43 15.41 17.1 16.86
15 15.9 20.66 14.39 16.44 15.47
20 15.72 19.94 13.83 15.48 14.65
25 15.6 19.26 13.48 15.12 14.09
30 15.34 18.61 13.23 14.52 13.67
35 15.04 18.01 13.06 14.28 13.35
40 14.7 17.43 12.92 13.92 13.09
50 14.64 16.38 12.73 13.56 12.69
0
20
40
60
80
100
120
140
0 50 100 150 200 250 300 350 400Infi
ltra
tion R
ate
(cm
/hr)
Time, t (minutes)
Observed Infiltration rate (cm/hr)
Infiltration rate by Horton’s model (cm/hr)Infiltration rate by Green-Ampt model (cm/hr)Infiltration rate by Kostiakov model (cm/hr)
Infiltration rate by Philip’s model (cm/hr)
40 Sreejani TP et,al
60 14.4 15.45 12.06 13.2 12.39
70 12.64 14.61 12.51 12.72 12.17
85 12.32 13.53 12.41 12.6 11.9
100 11.88 12.62 12.34 12.24 11.7
115 11.32 11.85 12.29 11.96 11.54
130 10.92 11.2 12.25 11.72 11.41
145 10.32 10.66 12.22 11.56 11.3
160 9.72 10.21 12.19 11.36 11.2
190 8.76 9.5 12.15 11.14 11.04
220 7.8 9 12.13 10.9 10.92
250 7.8 8.65 12.1 10.68 10.82
Correlati
on
Coefficie
nt
-
0.97
0.82
0.99
0.92
Standard
Error
-
1.14
1.92
0.53
1.47
Figure 5: Variation of experimental and calculated infiltration rates at Dispensary-
AU
0
5
10
15
20
25
30
0 50 100 150 200 250 300
Infi
ltra
tio
n R
ate
(cm
/hr)
Time, t (minutes)
Observed Infiltration rate (cm/hr)
Infiltration rate by Horton’s model (cm/hr)Infiltration rate by Green-Ampt model (cm/hr)Infiltration rate by Kostiakov model (cm/hr)
Infiltration rate by Philip’s model (cm/hr)
A Study on Infiltration Characteristics of Soils at Andhra University … 41
Table 6: Experimental Vs Calculated infiltration rates at Assembly Hall-AU
Time
(min)
Infiltration rate (cm/hr)
Experiment
al value
Horton’
s model
Green-
Ampt
model
Kostiak
ov
model
Philip’s
model
2 6.22 5.73 7.1 6.9 6.83
4 5.21 5.29 4.67 4.5 5.05
6 4.57 4.9 3.84 3.9 4.26
8 4.16 4.55 3.41 3.6 3.79
10 3.96 4.23 3.13 3.3 3.47
15 2.92 3.58 2.81 3.12 2.97
20 2.74 3.08 2.62 2.76 2.67
25 2.46 2.69 2.49 2.52 2.47
30 2.43 2.39 2.4 2.4 2.32
35 2.25 2.18 2.34 2.28 2.2
40 2.12 2.01 2.28 2.22 2.11
50 1.7 1.78 2.22 2.16 1.96
60 1.46 1.64 2.17 2.04 1.86
70 1.46 1.57 2.14 1.92 1.78
Correlati
on
Coefficie
nt
-
0.97
0.92
0.99
0.98
Standard
Error
-
0.33
0.51
0.18
0.27
42 Sreejani TP et,al
Figure 6: Variation of experimental and calculated infiltration rates at Assembly
Hall-AU
From the results it is found that the values of parameters of Infiltration models vary
from soil to soil and from place to place. Also the Correlation Coefficients and
Standard errors are different for the soils at different locations as calculated. From the
analysis it is found that for all regions selected in the study area, Kostiakov’s Model is
best fitting with high degree of Correlation Coefficient and Minimum standard Error.
The values of Correlation Coefficient and standard Error for soils at different
locations in the study area for Kostiakov’s model are 0.99 & 0.89 for soil at NCC
respectively, 0.99 & 0.24 for soil at CSE Department respectively, 0.99 & 2.94 for
soil at Samatha Hostel respectively, 0.99 & 0.53 for soil at Dispensary respectively,
0.99 & 0.18 for soil at Assembly Hall respectively. From the graphs drawn on
variation of infiltration rates, it is observed that, initially rates are higher and
decreased with time up to a steady state infiltration rate.
Conclusions
From the present study it was found that constant infiltration rates of selected five
locations of the study area i.e. at NCC, CSE Dept., Samatha Hostel, Dispensary and
Assembly hall are 2.68, 2.06, 17.43, 7.8 and 1.46 respectively. The values of
parameters of infiltration models vary from soil to soil and place to place. The values
of unknown parameters of Horton’s, Green-Ampt, Kostiakov’s and Philip’s model are
0
1
2
3
4
5
6
7
8
0 10 20 30 40 50 60 70 80
Infi
ltra
tion R
ate
(cm
/hr)
Time, t (minutes)
Observed Infiltration rate (cm/hr)
Infiltration rate by Horton’s model (cm/hr)
Infiltration rate by Green-Ampt model (cm/hr)
Infiltration rate by Kostiakov model (cm/hr)
Infiltration rate by Philip’s model (cm/hr)
A Study on Infiltration Characteristics of Soils at Andhra University … 43
shown in table 2. From the correlation coefficient and standard error calculations it
was found that for the soil and their conditions in the study area Kostiakov’s model is
best fitting with high degree of correlation coefficient and minimum standard error.
Kostiakov’s Infiltration model parameters of soils of Andhra University region are
estimated. The unknown parameter ‘a’ ranged from 2.723 to 60.322 and another
parameter ‘b’ ranged from 0.533 to 0.855, where ‘a’ and ‘b’ are local parameters. The
estimated values are substituted into the model equation to obtain the specific
infiltration equations for the soils of the study area. The model equations estimated in
this study area at selected five locations are Fp = 6.228t0.533, Fp = 5.394t0.778, Fp =
60.322t0.786, Fp = 15.222t0.855 and Fp = 2.723t0.719 for soils near NCC, CSE Dept.,
Samatha Hostel, Dispensary and Assembly Hall Respectively, where ‘Fp’ is in cm/hr
and ‘t’ is in hours. The obtained infiltration equations could be used to estimate
infiltration data at any time‘t’ for the soil of this area. This research work seeks to
save time and cost of field measurement during soil water management and water
resources conservative practices in this area. Double-ring-Infiltrometer (DRI) is
frequently used to estimate infiltration because the procedure is rather straight
forward and the instrumentation is simple, but the measurements are time-consuming
and tedious. From the present study it is found that the soil condition affects the
infiltration rate. The factors affecting infiltration rates are soil moisture, type of soil
medium, permeability, vegetal cover, surface fines, soil compaction, water holding
capacity, depth of surface detention, temperature of water etc. From the graphs of
infiltration rates against time it is found that initially infiltration rates were high and
decreased with time up to constant infiltration rate. To increase the infiltration rates of
the area infiltration facilities such as Rain Gardens, Vegetated filter strips, Porous
Pavements, Infiltration Planters, Grass Swales, Infiltration ponds etc.. Should be
adopted based on site conditions and economy.
Acknowledgements
The authors acknowledge Department of Science and Technology (DST), New Delhi
and Andhra University, Visakhapatnam for sponsoring a Research project under
which the present work is carried out.
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