A project dissertation submitted to the Universiti Teknologi PETRONAS Civil Engineering Program in partial fulfillment of the requirement for. Stormwater was identified as one of the factors causing surface runoff on land. Runoff is caused by the inability of water to penetrate the soil, causing the water to remain in the soil and causing major problems such as flooding and puddles.
A rain garden promotes infiltration into the soil below, reducing surface runoff thereby solving flooding problems. The objective of this study is to investigate the effects of soil media composition on hydraulic performance in a rain garden system. In order to analyze the hydraulic performance of the system, several parameters have been identified as indicators in this study, which are water flow, soil hydraulic conductivity, water removal efficiency and water holding capacity.
A coarser grained material was known to give greater flow and hydraulic conductivity, however, an addition of fine sand and leaf compost helps with water removal and drainage, which is also a parameter good for a better rain garden system. First of all I want to thank Almighty Allah for His willingness that I was able to complete my final year project and for His goodness I was given a good health condition during the completion of the project.
INTRODUCTION
- Project Background
- Problem Statement
- Objective
- Scope of Study
From a landscaping point of view, a rain garden can be a new concept in gardening and beautification. Plants not only improve the appearance of the garden, but can also improve the performance of the rain garden in terms of hydraulic conductivity (Asleson et.al, 2009). Maintenance is a must to ensure that the rain garden can function effectively and to prevent problems.
Another sign that the rain garden is not effective is the presence of wetland sycamores such as cattails and arrowheads (Asleson et.al, 2009). The primary function of the rain garden is to act as a bioretention that can retain a certain amount of water underground to prevent an increase in surface runoff. Each type of soil mix has a different impact on the hydraulic performance of the rain garden.
The aim of the study is to investigate the effects of different artificial soil compositions on the hydraulic performance of rain gardens. Rain garden hydraulic performance includes outflow, hydraulic conductivity, and efficiency in terms of water removal through the soil mix.
LITERATURE REVIEW
- Bioretention
- Hydraulic Conductivity
- Infiltration Testing Method
- Darcy’s Law on Hydraulic Conductivity
Hydraulic conductivity can be defined as a measure of a soil's ability to transmit water. Under saturated conditions, this parameter is usually denoted as Ksat or (Ks) and is assumed to be constant for a given space and time within a soil (Amoozegar and Wilson, 1999). Ksat knowledge of a specific soil is very important for example. in drainage design, saturated hydraulic conductivity is used to calculate the rate at which water can move to and in drainage lines below the water table (Amoozegar and Wilson, 1999). Some of the most influential factors are soil porosity, particle size, and soil density.
Porosity refers to the number of voids or holes in the soil particle, while bulk density is the measure of soil mass per unit volume of soil. The advantage of field tests on soil is that the soil is undisturbed and the result can accurately represent the actual situation. However, these measurements depend on the properties of the soil such as the soil's disturbed or undisturbed nature and size of particles.
In the soil texture series, sand is the coarsest of the textures in the soil group. Because the sand is larger in the group, it has the highest permeability, allowing for greater water infiltration. Porosity is the ratio between the area of voids and the total volume of the deposit.
There are methods by which hydraulic conductivity testing can be done, either in a controlled environment (laboratory) or field testing. Asleson (Asleson et.al, 2009) had done the infiltration rate test in the rain garden using the modified Philip-Dunne Infiltrometer, which places an infiltrometer in the soil to determine how quickly water will be able to infiltrate on the ground. From the illustration, H₀ is the initial height if the water, H(t) is the height of the water at a given time, Lmax is the depth of penetration into the ground, r₀ is the equivalent radius of the source, r1 is the radius of the cylinder, r is any radius within of the wetted front, and R(t) is the radius at the sharp wetted front at time t.
Darcy's law and the mass conservation equation are equivalent to the groundwater flow equation, one of the basic relationships of hydrogeology. The proportionality constant Ks is the hydraulic conductivity in the s direction, a property of the geological medium. Hydraulic conductivity is a measure of the ease with which a medium transmits water; Materials with higher Ks allow water to pass more easily than materials with low Ks.
If there is flow in the positive s direction, Qs is positive and dh/ds is negative. Conversely, when flow is in the negative s direction, Qs is negative and dh/ds is positive.
METHODOLOGY
Study Methodology
Apparatus and Equipment Setup
- Design discharge
- Design dimensions of sand column
- Design of layers in the sand column
Other parameters can also be known from the designed column discharge. In the layer design according to the MSMA bioretention impermeable rain garden design, the column is separated into several layers to serve different functions in the experiment. The layer consists of small cobblestones that are relatively flat and range in diameter from 3.0 mm to 6.0 mm.
The layer is made thin to avoid errors in the experiment as the stones will affect the discharge of water flowing from the column. A net layer is also placed between the drainage layer and the soil layer to prevent clogging and to distinguish between the layers. Engineered soil will consist of the sand with different types and dimensions, and leaf compost, which consists of ground dry leaves.
The mixture proportions are varied to see their effect on the rate of water infiltration. A pond is an above-water layer above a layer of mulch that holds water above a layer of sand. The ponding layer is made to simulate the condition during a storm, when water collects on the ground before percolating into the ground.
RESULT AND DISCUSSION
Overall Result of the Experiment
Graphical Comparison
- Flow of Water based on different engineered soil composition
- Hydraulic conductivity of soil based on different engineered soil composition
- Percentage of water removal based on different engineered soil composition
The graphs show that the reductions in hydraulic conductivity with and without leaf compost are in a similar pattern. The use of coarse sand gives a higher value of hydraulic conductivity, and with the addition of fine sand these values decrease. When adding leaf compost, the effects in terms of improving hydraulic conductivity are rather insignificant.
From graph 13 it can be seen that the hydraulic conductivity for each case of fine sand addition is lower than the cases where leaf compost is not involved. Therefore, it can be said that the leaf compost reduces the hydraulic conductivity of an engineered soil instead of improving them. Another parameter observed in this experiment is the water removal efficiency of the engineered soil, which is represented in Figures 14 and 15.
From the graphs, it can be seen that the efficiency of water removal is greater with the addition of leaf compost. Without leaf compost, water removal can go up to 90.2%, however, the test with leaf compost gives a water removal efficiency of approximately 94.2%. The difference may be due to the difference in hydraulic properties between sand and leaf compost.
Therefore, it can have other properties, which can remove the water in a larger volume than just sand.
CONCLUSION AND RECOMMENDATION
As can be seen from the results of the study, a random dry leaf is used as leaf compost. In future studies, another organic material should be tested to find one that performs better than leaf. Another compost material that can be tested includes vegetation waste as this can be very economical and environmentally friendly.
Mulch layer and vegetation can be included in future studies to represent the real outdoor situation. The inclusion of mulch can have a positive influence on the performance of the rain garden. Hunt III, P.E., M.ASCE (2010) "Impacts of Construction Activity on Bioretention Performance." Journal of Hydrological Engineering, Vol.
The Impact of Media Depth on Effluent Quality and Hydrologic Performance of Undersized Bioretention Cells." Journal of Irrigation and Drainage Engineering, Vol. Effect of Stormwater Runoff on Clogging and Reduction of Faecal Bacteria in Sand Columns." Journal of Environmental Engineering, Vol. Shepherd, (1990), Correlations of Permeability and Grain Size, Journal of Department of Geological Science, University of Kentucky, Vol.
34;Hydraulic performance of biofilters for stormwater management: First lessons from both laboratory and field studies." Water Science and Technology, Vol 56 No 10 pp 93-100, IWA Publishing 2007.
