Kouli_etal_2008_Groundwater modelling_BOOK.pdf - Pantelis ...

8
Goloka Behari Sahoo and Chittaranjan Ray
Table 1. Continued
Item
no
Parameter
8 Distance to streams or
other contaminant sources
Type of data collected
Rang-specific data (m)
Actual /rangespecific/descriptive
data
arranged in recognized clusters
for ANN modeling
Model
value
≤30.5 2
>30.5 1
9 Well-site topography Descriptive data
10 Season of sample collection Descriptive data
11 Presence of irrigation well Descriptive data
12 Spill or disposal site Descriptive data
13 On-site pesticide storage Descriptive data
14 Presence of animals Descriptive data
15 Aquifer class Descriptive data
Level land 4
Hill top 3
Depression 2
Hill slope 1
Fall 4
Winter 3
Spring 2
Summer 1
Yes 2
No 1
Yes 2
No 1
Yes 2
No 1
Yes 2
No 1
Sand/gravel 2
bedrock 1
16 Pesticide leaching Actual concentration
(μg/L)
Real index value (0.1 to 10.0)
Index
value
4. Analysis, Results and Discussions
4.1. Pre-processing of Input Data
Repetitive data (i.e., two or more identical input samples and each having a different target)
undermine ANN training (ASCE Task Committee, 2000). Because of the categorical inputs
for all 15 input parameters and pesticide concentration index as the target, a few repetitive
samples are found in the dataset. All repetitive samples are replaced by one input sample and
the average target value (i.e., the average pesticide concentration index) of all similar
samples, thus reducing the total available 631 samples to 572 samples. Moreover, the data are
scaled from 0 and 1 before presenting to ANN for training, validating, and testing.