Geotechnical Assessment of Soil Permeability in Land Development Areas

Infiltration is identified as one of the best operational and sustainable methods to handle urban storm water. Until recently, in stormwater management designs and selection of best stormwater management strategies, permeability value of different soils were not been considered as major factor. Due to the increasing housing density local land development authorities requires storm water runoff from developing lots to be retained/detained within the property. Due to lack of information on local soil properties, specifically permeability rates within the soil predominant in land development areas, it is difficult to assess storm water retention/detention requirement. This case study was carried out within the new development areas in Gosnells in Western Australia mainly focusing on identification of different soil types with respect to their infiltration capacities in selection of best stormwater management strategies. The Guelph Permeameter have been used to investigate the saturated permeability of different soil types. Based on the above tests, the results have been categorized in to four main types of permeability groups; Very Rapid (> 1.56 m/day), Rapid (0.48<1.56 m/day), Moderate (0.12<0.48 m/day) and Slow (<0.12 m/day). Finally, with the help of the existing soil map, the point represent permeability data were been generalized logically. These results have been used to develop permeability maps representing the areal average. The soil types and their observed permeability values compared with the literature; soil classification data of Department Agriculture. The comparison shows that field test data has a higher agreement with literature based soil classification. These field tests will be extended to identify the best stormwater management practices for the selected land development areas. The result will be useful for land developers as well as authorities, decision makers and policy makers to come up with sustainable land development strategies

Assessment of Infiltration Based Urban Stormwater Management for Residential Land Development

This research established a statistically significant broad approach to assess the infiltration based stormwater management concept and its application to urban land developments. The study has developed an inventory and mapping of soil characteristics using field and laboratory tests, towards developing stormwater management strategy guidelines in selecting the best stormwater management strategies in urban land developments. The outcome of this study will be useful for scientific community, authorities and decision makers for sustainable land developmen

Correlation of Soil Permeability and Particale Size Distribution with Respect to Urban Stormwater Management

The most challenging factor for stormwater management at source control concept is the soil permeability. Soil permeability plays an important role in this process as the infiltration values change from one place to another even in the same soil type and the same horizontal profile. The percentage availability of gravel, sand, silt and clay in a particle size distribution of a soil sample is one of the major factors that directly influence its permeability. Particle size distribution tests and laboratory permeability tests were performed for 90 randomly selected undisturbed soil samples collected at 1.5 m depth from the existing ground level. Two analyses were required to be conducted on the test results. The primary analysis of particle size distribution involved categorising them using the Unified Soil Classification system by plotting the sieve analysis graphs which were based on their percentage availability of different particle sizes. The secondary analysis investigated the relationship of soil permeability with respect to the percentage availability of silt and clay. The results indicated that the permeability value varies in a range from 0 to 20 m/day while the percentage of silt and clay varies from 0 to 10%. Moreover the secondary analysis clearly showed that soil permeability can be greatly varied in a particular range of same silt and clay percentage which might help in understanding the behaviour of soil permeability considering the other factors such as density, void ratio and porosity

Geotechnical investigation of the relationship between physical properties and saturated hydraulic conductivity by using the empirical formulas

Historically geologists, engineers, and soil scientist have conducted many field and laboratory tests to find the best soil permeability values for their design, identifying the fundamental relationships between the soil properties and the soil permeability it still remains inadequately quantified. As the soil permeability changes from one place to another, even in the same soil type and the same horizontal profile, the determination of the correct soil permeability value has become more challenging. Many different techniques have been proposed to quantify the hydraulic conductivity including several empirical formulas. Most of the empirical formulas overestimate the value of soil permeability even in the same soil sample and some of the values are not directly applicable in a physical environment due to the theoretical enforced limitations. However, accurate estimation of soil permeability in the field environment by the field methods is also limited by the lack of precise knowledge and equipment and the cost of any additional field operations involved. Therefore this case study was focused on identifying the most effective soil parameters which govern the value of saturated hydraulic conductivity and to check the applicability and the reliability of comparing the use of existing empirical formulas to the experimental test results

Effectiveness of Stormwater Best Management Practices in Urban Land Developments

Australian local governments urge to practice the water sensitive urban designs and best management practices in urban land development processes to protect the pre-development hydrology in the post- development stage. This usually comes with the best management practices guided by the local governments and environmental protection authorities. Under the best management practices, one criterion is retaining runoff from post development 1 year 1 hour Average Recurrent Interval (ARI) event within the development site for runoff quality control by treating the initial runoff as close as to the source. In this study, soakage wells, bio retention swales and rainwater tanks were modeled to cater 1 year ARI runoff within the development. Their impact on reduction of required 5 year and 100 year ARI event runoff storage was studied. One of the Western Australia’s residential development consist of about 118 ha was selected as the case study. The XPSWMM hydrodynamic computer model has been used to do the numerical modeling. It has shown 70% of 5 year runoff volume and 34% 100 of year required storage capacities has been reduced by applying above best management practices. Cost effectiveness of the methods used to cater 1 year ARI event was discussed. The results will be used to develop the urban water management plan for the development site

Water supply adaptation for changing water sources: introduction to movable water treatment plant

Climate change has significant impacts on water resources and particularly has detrimental impacts on water supply and management of water sources. Although Sri Lanka has a tropical climate with little seasonal variation, Sri Lankan climate has experienced vast changes in the last few decades. Due to these changes, it is really difficult task to find a reliable and long term water sources for supplying drinking water to the people who are living in isolated areas. On the other hand, the changes of river basin characteristics due to urbanization and industrialization are aggravating this problem. Increasing demand for treatment facilities of surface water due to above reasons and lack of funds to implement enhanced water treatment facilities are the major problems encountered at present. The concept of a locally made movable type surface water treatment plant emerged with the objectives, to be maintained the drinking water quality standards due to changing the raw water quality of water sources and facing disaster situations as floods, tsunami or earthquake. There is a rising demand for cheaper, easy to build, movable type water treatment unit operation modules which are an effort to reintroduce conventional water treatment modules using low cost construction materials and prefabrication techniques to achieve less construction time and movability of the modules.This study explains an approach to achieve these goals at affordable and sustainable manner. Prime objectives of this project is to create a water treatment plant of shorter construction period, affordable capital investment, capability of moving the plant to different locations when needed and to be a viable in 500 to 1000 m3day capacity in range. The introduced movable water treatment system basically includes three modules; tube settler, chlorine contact tanks and rapid sand filter. As a pilot project, these modules have been integrated at two main water supply schemes in Sri Lanka at Pugoda and Mahiyangana. Detailed assessment has been carried out to test the performance of the system as well as an economical assessment have been carried out. The assessment output highlights the suitability and high performances of the introduced systems. Output of this study will assist water resources managers and decision makers to face the future challenges related to impacts of climate change on water resources and drink water supply

Maximize the benefits of water sensitive urban designs in a local government area: Western Australia

Until recently, stormwater management strategies have failed to adequately consider the criticality of spatially varying soil permeability values and their implications on drainage designs. This case study was carried out in new development areas, focusing on identification of soil properties and development of a typology of suitable stormwater management strategies with respect to applicable infiltration capacities. The Guelph Permeameter was used to investigate the in-situ saturated hydraulic conductivities. Test results were categorized into four main permeability groups, very rapid (> 1.56 m/day), rapid (0.48<1.56 m/day), moderate (0.12<0.48 m/day) and slow (<0.12 m/day), based on the theoretical requirements of stormwater management techniques. Finally, with the help of the existing soil maps, the point represent hydraulic conductivity data were been generalized logically in order to develop the hydraulic conductivity maps representing the areal average as an electronic shape files by using a GIS Arc view mapping software. The future development areas under Central Maddington, Kenwick, Central and Outer Beckenham have been identified as low permeable areas which is not suitable for infiltration based stormwater management strategies whereas the Landford, Thornlie, North Huntingdale and Gosnells has been identified as high permeable areas which is highly recommended for infiltration based stormwater management strategies

An innovative approach to stormwater management accounting for spatial variability in soil permeability

In the past few years, major flooding incidents have been experienced in Australia. This has resulted in increased concerns for local authorities, environmental institutions and the public, giving management of stormwater a new priority. Stormwater infiltration is one of the best practise methods to operationally and sustainably handle urban drainage. However, until recently, stormwater management strategies have failed to adequately consider the criticality of spatially varying soil permeability and their implications on drainage designs. With a lack of detailed information on local soil properties, it is difficult to assess the adequacy of stormwater retention / detention requirements. This study was carried out in new land development areas of Gosnells in Western Australia, focusing on identification of soil properties and development of a typology of suitable stormwater management strategies with respect to applicable infiltration capacities. The Guelph Permeameter and the falling head methods were used to investigate the in-situ and laboratory saturated hydraulic conductivities. Test results were categorized into four permeability groups; very rapid (> 1.56 m/day), rapid (0.48<1.56 m/day), moderate (0.12<0.48 m/day) and slow (<0.12 m/day). Finally, these four key permeability categories, combined with the scale of application (lot, street, regional) and operational objective (quality, quantity, conservation), enabled the identification of suitable stormwater management approaches. The results of this study will assist land developers, engineering consultants and local authorities to devise locally appropriate, functional and water sensitive drainage approaches