Correlational of soil permeability and infiltration rate at the ITERA infiltration drainage development plan

Physical development has an impact on the availability of groundwater. The limited water surface requires humans to manage available wisely. Institut Teknologi Sumatera (ITERA) is a state campus on the Island of Sumatera and has an area of 275ha. The eco-drain concept attempted to recover groundwater at all masterplan development. This study aims to reveal how much influence infiltration rate has on soil permeability in the ITERA Infiltration Drainage Development Plan. This research used quantitative research using a correlational approach by processing primary data and further analyzing it in the soil mechanics laboratory at the 8 points of the equal research location. Infiltration rate data was obtained using a double-ring infiltrometer and analyzed with the Horton Method, then the sampling at a depth of ±50 cm analysis with the Falling Head Method. Based on the result, there is no correlation between both tests and resulted in different soil types. The infiltration rate test result of the soil type is loamy sand – sandy loam with moderately – moderately slow infiltration classification. The soil permeability type is fine sand or silty clay with medium and low permeability, and the infiltration rate only affected 37.6% of the permeability soil result.


Introduction
Groundwater resource management is helpful for the availability of quantity and quality of water for life, health, and ecosystem sustainability.Soil investigation is necessary to determine the condition of the soil structure so that it can be used in the design of water structures and coherent information about the characteristics and properties of the soil and comply with the required design classification.Soil investigations are essential for the design of civil engineering works, especially water reservoirs.Soil investigations in water reservoir design are infiltration rate tests and soil permeability tests.Infiltration rate tests measure the quantity of surface water that enters the soil per time unit.The infiltration rate is valuable in predicting soil water infiltration zones and is related to the sub-surface water capacity.Soil with a high infiltration rate moves water quickly [1].Tests to measure the infiltration rate can be conducted on the soil surface at specific depths by employing a double-ring infiltrometer on vegetated or bare land.The test requires a dry period (no rainfall) of 3 to 5 days in the designated location [2].The factors that determine the runoff potential are drainage, infiltration capacity, saturated hydraulic conductivity, depth to the water table, and impermeable layer [3].Soil permeability indicates the soil's capacity to transmit water to underlying layers.Soil structure, texture, and organic matter content can improve the soil permeability rate [4].As the soil permeability value increases, so does the infiltration rate.Soil classification is the process of identifying the soil type of a location to determine its properties and characteristics.Soil thickness can inhibit the regulation of air from soil pores and retard water movement, thus reducing the permeability rate of soil [5].Clay-dominant soils have tiny pores.Sanddominant soils have large pores.Soil dominated by dust will have medium pores [6].The factors affecting soil permeability include the distribution of intergranular pores, void ratio, and degree of saturation [7].Soil permeability is the capacity of water to enter the soil through its pores, whether horizontally or vertically.Hydraulic conductivity (k) is the measure that describes the ability of soil to convey water.Darcy's law is used to analyze the permeability coefficient (k).The Constant Head Method is appropriate for soil testing like granular soil types, such as sand, gravel, and sand or silt mixture.These soils of this type are classified as high permeability due to their high bulk density (depending on the granular size distribution and the arrangement and density of the granules), whereas if the soil granules are fine-textured (cohesive), such as silt or clay, the Falling Head Method is used [8].
Soil with high permeability can increase the infiltration rate and decrease surface runoff.This study aimed to acquire the expected data by testing the place with two different methods (the infiltration rate test and the soil permeability test) to reveal how much influence infiltration rate has on soil permeability in the ITERA Infiltration Drainage Development Plan.The collected data is subsequently analyzed using the SPSS application to determine the relationship correlation between the two variables and whether they affect each other.

Material and Methods
Quantitative methods were employed in this study using a correlational approach.The chosen research method utilized numerical data throughout data collection, interpretation, and analysis of the results.The data analysis will demonstrate a linear relationship between the dependent variable (infiltration rate) and independent variable (soil permeability), revealing their association and influence.The research has a location on the Institut Teknologi Sumatera (ITERA), a government campus on the island of Sumatra, which covers an area of 275 ha.The research location was determined based on the development of an infiltration drainage plan.The analysis involved collecting primary data on infiltration rate, soil characteristics, and permeability values from 8 (eight) locations between December -June 2023 (Fig. 1).

Figure 1. A Map of Location Infiltrations Rate Measurement and Sampling Soils Permeability
Infiltration rates measurement used a double-ring infiltrometer installed on flat ground, whether bare or vegetated.The first step of the soil surface cleansed from vegetation.Next, install the double ring on a flat surface.The ring should be 10cm above the ground level.The soil is excavated to a specific depth, and sampling can be measured if there has been no rainfall for 3-5 days [2].Infiltration rate testing is applied to provide information on infiltration rates and infiltration capacity.The analysis results provide a classification of infiltration rates and soil types.Soil permeability sampling is executed at the same place as the infiltration rate test, and obtaining samples is conditional on this location being at the same point as the infiltration rate test and without rainfall.Three soil samples are taken to a depth of ±50 cm.They are later tested in the soil mechanics laboratory to determine the soil permeability classification based on soil type, texture, and compositionality.
The research procedure is divided into three stages:

a. Infiltration Rate Measurement
Infiltration is measured using a double-ring infiltrometer inserted into the soil to a 5 -10 cm depth, with both rings flat.A ruler is placed on top of the inner ring to measure the drop of water.Infiltration rate testing determines how much surface runoff and ponding can infiltrate.The infiltration rate is the velocity or amount of water that enters the ground surface per unit of time or the amount of water entering the surface per unit.The test requires a dry period (no rainfall) of 3 to 5 days in the designated location.The infiltration rate varies depending on the strength of the rainfall, and therefore, it is not consistent [9].Where the infiltrating rate (f) in cm/h is the change in the height of the water's surface per time interval (ΔH) in centimeters divided by the measuring time (t) in centimeters per hour, the equation is: The infiltration capacity refers to the soil's ability to absorb water or the maximum rate at which water can enter the soil during rainfall [10].The infiltration rate in a location decreases as soil saturation caused by water increases.At a certain point, the infiltration rate can reach a constant level.Analyze infiltration capacity using the Horton Method [10] [11].The equation is: Or: Where: The infiltration rate (f) based on infiltration observations starts from a default value (fo) and exponentially decreases to a constant state (fc).The Napierian logarithm base number (e = 2.718) has a constant value for the soil type (k), which is {-1/ (m log 2.718)} a constant reduction to the dimension [t-1], where time (t) is calculated from the start of rainfall (in hours The assessment is based on the infiltration rate classification used by US Soil Conservation (1996) [10] (Table 1).
Soil surface conditions are predominant factors that affect the occurrence of infiltration.Soil roughness, vegetation cover, and land use alter the water available on the surface, influencing the soil surface's collection and openness of pores with consequent effects [12].The texture of the soil can influence the infiltration rate.The most suitable soil type for designing an infiltration plan has a minimum infiltration rate of more than 3 mm/h.The minimum soil type is sandy loam [13].

b. Soil Permeability Measurement
Soil permeability samples were taken from the same site as the infiltration rate measurements at a depth of 50 cm from the soil surface using a hand borer.The test requires a dry period (no rainfall) of 3 to 5 days in the designated location.Soil permeability was measured in a laboratory.The falling head test was employed to measure the soil permeability samples because the fine soil contained silt and clay, a finding established through a granular texture examination of the soil.The falling head method can be solved by equation  =  ), thus the value of permeability (k), [5] is: The required variables for this measurement are the surface area of the piezometer device (a) in square cm 2 , the surface area of the soil sample (A) in square cm, the length of the soil sample (L) in cm, the initial height (h1) and the final height (h2), and the time taken to collect the water (t) in seconds.Soil permeability values can be classified based on the soil type.Soil types containing silt sand, fine sand, and dense silt with a permeability value (k) of 10-3 -10-5 cm 2 /sec should be classified as low permeability, while clay soil types with a soil permeability value (k) < 10-7 cm 2 /sec should be classified as an impervious permeability soil (Das, 2010) [14].

c. SPSS Correlation Analyze
Statistical analysis is the method used to process and analyze statistical data from infiltration rate and soil permeability tests.The method of the Pearson Bivariate Correlation with the IBM SPSS (Statistical Program for Social Science) application is used to determine the strength of the relationship between these variables.Linear regression analysis was done before analyzing the correlation between variables.This analysis aims to determine whether there is a significant linear relationship between these variables.The basis for decision-making is comparing the significance value (Sig.) and the F-count value with the F-table.If the value (deviation from linearity) Sig.> 0.05, which means that there is a significant linear relationship between the independent and the dependent variables.Conversely, if Sig. < 0.05, then there is no linear relationship between the two.For the F-count value with the F-table, if the F-count value < F-table, then there is a significant linear relationship between the independent and the dependent variables.Conversely, if F-count> F-table, no significant linear correlation exists between the two variables [15].
The bivariate Pearson correlation coefficient ranges from -1 to 1, with a value of 0 indicating no correlation (Ho, accepted).Meanwhile, a correlation of 1 means that the two variables are perfectly correlated (Ho, rejected).A stronger relationship between the two variables is present as the value nears 1 or -1, while a weakened correlation is present as the value approaches 0 [15].Bivariate Pearson analysis satisfies the requirements: (1.)If Sig. (2-tailed) < 0.05, a correlation exists between the variables to be correlated, but if Sig.If (2-tailed) > 0.05, not any correlation.If the value of r-count > r-table, the variables are correlated.If the value of r-count < r-table, the variables are not correlated.If the Pearson correlation value contains the symbols (*) or (**), the variables are correlated, but if there are no symbols (*) or (**), there is no correlation between the variables.A single symbol (*) indicates a significant correlation of 1% or 0.01, while two symbols (**) indicate a significant correlation of 5% or 0.05 [15].

Result and Discussion
The infiltration rate was measured using a double-ring infiltrometer, and the data obtained was analyzed using the Horton Method (eq.2,3,4) at 8 locations (Fig. 2).A validation process is necessary to determine the level of error or deviation that may be present.The MAE, NSE, and RMSE methods were selected to test the data.Based on the MAE, NSE, and RMSE test values, the Horton method shows that the infiltration rate value is closer to the field-measured results.The smaller the MAE value obtained, or the closer it comes to 0, the closer the value obtained by the method corresponds to the value of the infiltrate rate measured on site.The NSE value of the Horton Method obtained around 0.9 or NSE> 0.75 is included in the reasonable interpretation.The RMSE value shows that the Horton coefficient is smaller or closer to 0 (Table 3).The exponential Horton Method equation explains the correlation between measured infiltration rates.The mean value obtained across the eight measurement locations to predict infiltration rate characteristics at ITERA was R2 = 0.9653 (Table 4).Horton's infiltration capacity analysis results differ at each location (Fig. 3).Many parameters, such as soil density, vegetation, granular compaction, and soil texture, impact the infiltration rate.According to the R2 value (Table 3) of each measurement location, it determined that (Table 5) the lowest infiltration rate value of the place is 1.20 cm/hour for the infiltration rate classification is Moderately slow with the soil type is loam -silty loam, while for classification of the highest infiltration rate value of 6.00 cm/hour has a medium infiltration rate classification with the soil type is loamy sand -sandy loam.The mean infiltration rate of the research location is 3.15 cm/hour, the infiltration classification is moderately (medium), and the soil type is loamy sand -sandy loam.In (Table 6) of the sieve analysis test, the soil texture is differentiated based on the size of the granules that pass through the sieve by dividing it into 4 (four) types: gravel, sand, silt, and clay.The results mean that the entire location has a fine gradation soil, with more than 50% passing through the 200-mesh sieve with silt soil types.The lowest percentage for silt is 58.0592%, and the highest is 70.0846%.Based on these results, select the falling head method to analyze soil permeability.From the results of the soil permeability measurement (k) (Table 7) using the Falling Head Method (eq.5), according to that mean of permeability soil, the research location has medium to slow permeability values, with the soil types being fine sand and silty clay.The mean soil permeability of the research location is 0.000691 cm/hour, the typical permeability is low permeability, and the soil type is silty clay.
Statistical analysis is used in the processing and analysis of infiltration rate data and soil permeability data to determine whether there is a correlation between the infiltration rate measurement by Horton's method and the results of laboratory soil permeability measurements at the same point.Infiltration rate measurements using a double ring infiltrometer according to [1] and soil sampling at the same place followed by laboratory permeability measurements.Correlation analysis using SPSS application with Pearson correlation and linear regression methods.From the linearity test analysis, according to (Table 8) to the Significant (Sig) value, which is 0.269 <0.05, there is no significant linear correlation between the variable infiltration rate and the soil permeability value.According to the F-value where the value of F-count df (deviation from linearity; within the group) is 1;5, then based on the F0.05 distribution table, the F-table value is 6.61, the F-count value is 6.61> 1.546 (F-count value bigger than F-table), concluded that there is no significant linear correlation between the two variables.The analysis (Table 9) results that the significant value (Sig.)(2-tailed) between soil permeability and infiltration rate is 0.106> 0.05 or the significance value is smaller than 0.05, is concluded that there is no significant correlation between the two variables, for the r-count value where the r-table 5% is 0.613 < 0.707, concluded that there is no correlation between the two variables.For simple linear regression between infiltration rate and permeability (Table 10), the coefficient of determination (R-square) is 0.376, which means that the influence of the independent variable (infiltration rate) on the dependent variable (soil permeability) is 37.6%.The R-square value indicates that the permeability parameter influences 37.6% of the infiltration rate, while the remaining 62.4% is affected by other parameters.The relationship curve between infiltration rate and soil permeability indicates a positive trend (Fig. 4), as the infiltration rate increases, soil permeability increases as a result.

Conclusion
The infiltration rate and soil permeability examination at the 8 points of the equal research location resulted in different soil types.Based on the results, it was determined that there is no correlation between both tests, which resulted in different soil types.The infiltration rate test result of the soil type is loamy sandsandy loam with moderatelymoderately slow infiltration classification.While the soil permeability the soil type is fine sand or silty clay with medium and low permeability.Soil permeability only affected 37.6% of the infiltration rate.For further investigation, recommend that a sample of the soil to a depth of 150cm rather than 50cm by the minimum depth requirements for infiltration wells.
This research is the initial stage in the design of modifications between drainage structures and groundwater infiltration structures.Many things can be developed in this research.One related to groundwater infiltration is research on the effect of soil permeability (hydraulic conductivity) and water infiltration behavior (velocity flow, discharge, groundwater recharge time).
time value (t) obtained from,  =

Figure 2 .
(a) Results of Field Infiltration Rate Measurement; (b) Results of Infiltration Rate Horton Method

Figure 4 .
Figure 4. Correlation between Infiltration Rate and Soil Permeability

Table 3 .
Validation Data of Field-Measured Results and Horton Method Result

Table 4 .
Linear Regression Coefficient at 8 Different Locations Figure 3. Regression Plots were Created at Eight Different Locations, Measured and Calculated Infiltration Rates with Regression Coefficients (R 2 ) and Equations for Each Measurement Point

Table 5 .
Analyze of Classification of Infiltration Rate

Table 6 .
Percentage of Soil Gradation from Wet Soil Mess at 8 (Eight) Different Locations

Table 9 .
Result in Correlation between Infiltration Rate and Permeability of Soil