WSUD Techniques for Urban Development with Focus on Saltwater Intrusion Problem, A Case Study of Kedonganan Village - Bali

Water is one of the most important resources in human’s life, and groundwater known as the largest freshwater source in the world. Along the development of the cities and population growth, the demand for water supply is also increasing. With the increasing of the freshwater needs, groundwater is also widely used for human’s daily activities. However, the irresponsible use and exploration of groundwater also certainly generate many problems, one of those is saltwater intrusion. Many coastal areas in Indonesia are starting to face saltwater intrusion problem which cause groundwater is no longer be used properly by the community. Therefore, the problem of saltwater intrusion needs to be addressed. This research aims to see the WSUD techniques which can be applied to prevent saltwater intrusion in coastal areas with Kedonganan Village as a case study. The research methodology used is descriptive qualitative method. For the result of this research, those are some WSUD techniques which can be applied in urban development to prevent saltwater intrusion occurs: rainwater tank, downpipe diverters, biofilters, infiltration basins & trenches, soakwells, swales & buffer strips, and pervious paving which have focus on accelerate infiltration into the aquifer.


Introduction
Water is one of the most important resources that needed in human life and all living things.In fact, the level of energy demand and the need for clean water is increasing along with the increase of human population.Water use has been growing globally at more than twice the rate of population increase in the last century [1].However, there are still many people who do not care and maintain the quality of existing clean water resources, which causes the need for clean water for life is not balanced with its availability.Many countries in the world are starting to face fresh or clean water crisis which has an impact on people's quality of life.This clean water crisis is also occurring in Indonesia, especially in Bali.Realizing that there are many problems related to water occur, many countries are developing policies and regulations related to climate change, water quality, flood risk management, environment, public health, and general concept of sustainability.Approaches for water management concept is really needed in area development planning.Water Sensitive Urban Design (WSUD) is one part of the concept of a green infrastructure approach with the aim of approaching urban planning and design related to water resources and environmental management as well as minimizing the impact caused by the presence of surface water in urban areas [2].Water Sensitive Urban Design 2 (WSUD), originally an Australian concept, recognizes and attempts to overcome these challenges by integrating water into urban development and planning from the earliest stages to maximize the opportunities for sensitive water cycle management [3].Water Sensitive Urban Design (WSUD) focuses on solutions that integrate the water cycle with the local context [4].Each Australian state develops its own WSUD policy and implementation strategy according to the context and focus of the conditions and problems of each region.In Bali, the demand for clean water is also increasing every year.Tourism activities are listed as influential factors in increasing the need for clean water in Bali.Bali Water Protection (2019) stated that clean water needs for tourism activities in Bali are 15 times greater than clean water needs of local communities.This condition certainly has negative impact for those existing water resources.In some areas, especially in southern part of Bali, groundwater level has been recorded to have decreased by more than 50 meters in less than 10 years and many wells have started to dry up or become polluted [6].The phenomenon of groundwater subsidence that occurs is caused by the high rate of groundwater exploration which is inversely proportional to the rate of reimbursement.The high level of groundwater exploration can cause coastal areas to be very vulnerable to saltwater intrusion.Saltwater intrusion such a very big problem to coastal communities that rely their livelihood on fresh groundwater supplies.Kedonganan is a village that located in the sub-district of Kuta, Badung, Bali, Indonesia, which known as its fisheries sector, as well as the beautiful Kedonganan Beach.Based on Regional and Tourist Attraction data by   measures.Avoidance measures are those which avoid the generation of contaminated stormwater runoff from allotments [11].WSUD techniques that belongs to the category are: preserve and maintain waterways and riparian areas, erosion and sediment control, street sweeping and litter control, urban design/housing design, rainwater tanks, downpipe diverters, permeable paving, green roofs and walls.Mitigation measures are those which are typically implemented to detain and treat stormwater runoff [11].WSUD techniques that belongs to the category are: gross pollutant traps, vegetated swales, gully baskets, bioretention, wetlands, floating wetlands, water smart street trees. 4

WSUD in Western Australia (WA)
Water Sensitive Urban Design concept with the aim of protecting groundwater and aquifers is the dominant focus of consideration in Western Australia.Protection of groundwater and aquifers is important because Western Australia relies on groundwater as the main source of clean water.One of the capacity building programs developed by WA Government is New Waterways Program organized by the WA Department of Water.Policy in Western Australia supports urban water management plans (UWMPs) and water management strategies as planning tools for setting and managing water quality targets to prevent groundwater contamination [4].Urban water management takes into consideration the total water cycle, facilitates the integration of water factors early in the land planning process, and encourages all levels of government and industry to adopt water management and urban planning practices that benefit the community, the economy and the environment [12].WA Department of Water has published several brochures containing information on concepts and techniques related to Water Sensitive Urban Design.The information in the brochure provided is used to assist those involved in urban design.Listed from the official website of the Government of Western Australia Department of Water and Environmental Regulation [13], the concepts and techniques described include: 1. Biofilters Biofilters, also known as biofiltration systems, bioretention systems and rain gardens, are excavated basins or trenches.To remove pollutants from stormwater runoff, biofilters are filled with porous filter media and planted with vegetation.They use natural and physical processes to treat stormwater.Biofilters can be used or applied in precinct (subdivision), street, and lot.

Constructed Wetlands for Stormwater Management
Constructed wetlands are extensively vegetated water bodies that use sedimentation, filtration, and biological uptake processes to remove pollutants from stormwater [13].In general, constructed wetland not suitable for the area where contaminated or nutrient rich groundwater is intercepted.To build constructed wetlands significant land area is usually required.Constructed wetlands for stormwater management usually used or applied in district and precinct (subdivision).

Dry or Ephemeral Detention Area
Dry or ephemeral detention areas are depressions that temporarily hold stormwater and release it at a slower rate than it comes in [13].Dry or ephemeral detention area have a purpose to reduce flow velocities and help to prevent downstream erosion.This concept also developed to improve stormwater quality primarily by allowing sedimentation of particle-based contaminants.They drain after each storm event to provide the full storage volume for the next one.Dry or ephemeral detention area method can be used or applied in district and precinct (subdivision).

Infiltration Basins and Trenches
Infiltration basins are depressions designed to capture and store stormwater prior to infiltration into the soil profile [13].Infiltration trenches are located below ground linear devices.Before the infiltration process, stormwater is stored in infiltration basins and trenches.This concept can be used or applied in district, precinct (subdivision), and street.

Litter and Sediment Traps
Litter and sediment traps are devices that retain 'gross pollutants' (litter and debris greater than 5mm) and coarse sediments (particles greater than 0.5mm) [13].They are available in several configurations and designs.Litter and sediment traps are developed to capture gross pollutants and coarse sediments.This system can be used or applied in precinct (subdivision), street, and lot.

Living Streams
A living stream is a constructed or retrofitted stormwater conveyance channel that mimics the characteristics (morphology and vegetation) of natural streams [13].They also treat the rainwater they carry using physical and biological processes.Living streams also create diverse habitats for wildlife and can become complex ecosystems that support a wide range of plants and animals.This system can be used or applied in district and precinct (subdivision).

Pervious Paving
Pervious paving can be used as an alternative to traditional impervious hard surfaces used in roads, carparks, footpaths and public squares or plazas [13].Pervious pavement is developed to reduces runoff by infiltrates the rainfall into the soil below as soon as possible.Pervious pavement can used to be an integrated water storage system.There are many types of pervious pavements such as porous turf, porous asphalt, porous concrete, permeable paving, etc. Pervious paving can be applied on street and lot.

Rainwater Storage and Reuse System
Rainwater storage systems are a simple method of capturing rainwater, traditionally from roofs, for use as an alternative water supply source and to reduce consumption of scheme water [13].
They can also provide a high-quality source of water if they can be installed and maintained in accordance with recommended guidelines.Rainwater storage and reuse system can be used or applied in street and lot.9. Soakwells Soakwells are a commonly used small-scale method of increasing infiltration into the ground as a way of managing stormwater [13].They generally provide maximum infiltration area with a vertical perforated cylinder and an open or perforated base form.This system will work well on sandy soil.Soakwells can be used in precinct (subdivision), street, and lot.

Swales and Buffer Strips
Swales are grassed or vegetated broad, shallow channels used to collect and convey stormwater flows, promote infiltration, reduce stormwater peak flow rates and discharge volumes, and remove sediments [13].Swales system is a combination of physical and biochemical processes to treat stormwater.Buffer strips are vegetated areas that reduce sediment loads from water flowing through them.Buffer strips are aligned perpendicular to the water flow [13].They are commonly used in conjunction with swales, living streams and constructed wetlands.Swales and buffer strips can be used in district, precinct (subdivision), street, and lot.Stormwater management involves a continuous chain of water quantity and treatment management elements that address hydrologic changes in urbanised catchments, including flooding impacts, water quality, water reuse and ecological objectives [12].There are 4 treatment train with their own urban water management objectives:

WSUD Data Needs
There are some data needed to support the application of WSUD concept and techniques.• Receiving waters These data are used to conduct initial analysis of the applicable system for the area.

Kedonganan Village
Based on the results of observations and secondary data collection carried out, some data related to the existing conditions of the study area were obtained which will be described as follows.

Nature of The Development
Currently, most of the land in Kedonganan Village has various functions.Based on the survey results, the functions and activities in the Kedonganan Village include: trade and services (beachside IOP Publishing doi:10.1088/1755-1315/1318/1/0120187 restaurants, Kedonganan Fish Market, supermarkets, mini markets, spas, etc.), fish pier, residences, hotels, government offices, and places of worship.

Topography
Kedonganan Village is a village in Badung Regency area with a slope of 0-5%, which is a coastal area.The land in the study area has a slope that tends to be flat.Based on the results of identification using the Google Earth application, the height of the study area is at a point 1-10 meters above sea level.

Soil Characteristics
The study area has an alluvium depositional area with regosol soil type.Alluvium deposits are clay, smooth, and can accommodate stagnant rainwater.Regosol soil is a type of soil which is a coarse grain derived from volcanic eruption material.Regosol soil is alluvial soil that is deposited.One of the characteristics of regosol soil is that it has coarse grains and has the ability to store water and low nutrients.

Groundwater
Groundwater aquifers in Badung Regency follow the general pattern of South Bali, those are: shallow aquifers are found at a depth of 30 -50 m with sloping formations to the south and confined aquifers or deep groundwater are found at a depth of 50 -150 m.The study area is included in the area with a well discharge of 5.0lt/second.This means that the area has a moderate category of groundwater content.The quality of groundwater in the Badung Regency area tends to experience a decrease in quality.Based on the results of groundwater quality research conducted by the Dinas Lingkungan Hidup Kabupaten Badung, groundwater in Kedonganan Village has a salty taste which indicates sea water intrusion.In the Kedonganan Fish Market area also noted to have high levels of Nitrate due to fish market activities, where the waste of internal organs of fish is dumped into channels or water bodies that lead to the sea [9].Based on the results of laboratory tests, high levels of TDS were also found in Kedonganan groundwater samples.

Local Climate Data
Badung Regency is included in an area with a tropical climate with 2 seasons: dry season in April -October and rainy season in November -March.Temperature and rainfall in study area were identified using data from Meteoblue website [15].The average rainfall in Kedonganan Village from January to December is 232.6 mm.The highest rainfall occurs in the rainy season in January, which is as much as 654 mm and the lowest rainfall occurs in the dry season in August, as much as 16 mm.The highest daily temperature in Kedonganan Village occurs in October, November, and December with temperatures reaching 33°C with an average temperature of 31°C.While the lowest daily temperature occurs in August and September with a temperature of 21°C at night with the lowest average temperature in that month is 24°C-25°C.The climatic conditions in Badung Regency are influenced by the movement of winds from the Australian Continent and the Asian Continent across the mainland of Bali Island in general, and Badung Regency in particular.Based on data collected from the statistical website Meteoblue, Kedonganan Village enters the area with an average wind speed of 20 km/hour -25 km/hour.The most frequent gusts of wind from the southeast have a speed of > 12 km/hour with the highest amount of time and from the south with the highest amount of time have the same speed of > 12 km/hour [15].Being on the equator makes Indonesia gets sunlight throughout the year with a long duration.The study area Kedonganan Village is included in the area with an average daytime duration of 11 hours 55 minutes [16].Based on the sun path diagram data seen in Bali, Indonesia -Sunrise, Sunset, Dawn and Dusk Times for the Whole Year (2021), sunlight in the study area tends to be on the north side in June and tends to be on the south side in December.At 12.00, an object with a height of 1 meter produces a shadow length of 0.33 meters with a UV index between 6-8.

Existing Drainage System
Kedonganan Village has not had its own wastewater treatment system.Currently, the drainage system used in Kedonganan Village is a conventional drainage system that is not yet connected to the nearest wastewater treatment system in Denpasar.The existing drainage system can be seen in the following figure which took a sample on Jalan Pantai Kedonganan.
Figure 2. Section of Jalan Pantai Kedonganan Moreover, Kedonganan Fish Market currently does not have a wastewater treatment plant in the market area but uses several holding tanks that are connected to each other.Wastewater from the Kedonganan Fish Market currently still uses a one-point collection system when it is full, the wastewater will be taken and brought to the nearest wastewater treatment plan in Suwung, Denpasar which is about 8.3 km from the design area [18].In the principle, in the Kedonganan Fish Market area, there are several wastewater collections tanks that end at one point, so when the point is full, the water will be taken and brought to the Suwung IPAL.However, in certain tanks, wastewater from the fish market is absorbed into the ground, when the soil is saturated and the tank is full, the wastewater will enter the tank afterward.The practice of infiltrating untreated wastewater into the ground certainly has a bad impact on the environment.The illustration of the wastewater reservoir in the area can be seen in the following figure.

Local Environmental Issues
Based on the results of the research conducted by Bali Water Protection, Badung Regency is included in an area with high groundwater exploration and susceptible to saltwater intrusion.This condition can lead to a decrease in the ground water level.When the groundwater level decreases and causes cavities in the aquifer layer, seawater intrusion into the aquifer becomes difficult to avoid.As a result, groundwater quality is no longer in good quality for consumption [5].Another issue is sea water pollution caused by waste from fish market activities.

Recommendation
Based on the existing condition data from the study area, it can be recommended to use the WSUD technique approach that focuses on maximizing capture rainfall and infiltration.Therefore, the possible techniques to be applied are: biofilters, infiltration basins and trenches, litter and sediment traps, pervious paving, rainwater storage and reuse system, soakwells, swales and buffer strips.In next regional planning, WSUD techniques also can be combined.An example of the application of the WSUD technique referred to in regional development can be seen in the following figure.

Recommendation
As the result of this study, it can be concluded that WSUD is not only focus on flooding as every Australian state has their own focus.Groundwater protection and aquifer improvement is a focus in Western Australia.WSUD techniques to be applied in focus with rainwater harvesting to prevent saltwater intrusion in Kedonganan Village are: biofilters, infiltration basins and trenches, litter and sediment traps, pervious paving, rainwater storage and reuse system, soakwells, swales and buffer strips.
To support this study, further studies are needed regarding the pollutant in study area.

•
Control the generation and treatment of sewage • Consider opportunities for daylighting culverts and urban channels 2. Manage water resources and abstractions to maintain groundwater levels and surface water flows 3. Promote and deliver water conservation • Reduce the use of potable water • Promote the harvesting of rainwater • Promote the use of greywater and effluent recycling 4. Integrate surface water management into developments • Protect water quality • Manage flood risk • Improve biodiversity and urban design 5. Protect public health by providing livable, resilient, and adaptable urban developments Each Australian state develops their own WSUD policy and implementation strategy according to the context and focus of the conditions and problems of each area.Protection of waterways ecosystem and conservation of coastal zones is a reference on the coasts of Brisbane, Melbourne and Adelaide, while groundwater protection is the dominant consideration in Perth [10].The illustration purposes of WSUD policies and tools of each state can be seen in the following figure.

Figure 1 .
Figure 1.Purposes of WSUD in Each Australian State Hoban (2019) grouped WSUD approaches into 2 categories: avoidance measures and mitigationmeasures.Avoidance measures are those which avoid the generation of contaminated stormwater runoff from allotments[11].WSUD techniques that belongs to the category are: preserve and maintain waterways and riparian areas, erosion and sediment control, street sweeping and litter control, urban design/housing design, rainwater tanks, downpipe diverters, permeable paving, green roofs and walls.Mitigation measures are those which are typically implemented to detain and treat stormwater runoff[11].WSUD techniques that belongs to the category are: gross pollutant traps, vegetated swales, gully baskets, bioretention, wetlands, floating wetlands, water smart street trees.

Figure 3 .
Figure 3. Illustration of Wastewater Reservoir at Kedonganan Fish Market

Table 1 .
WSUD Techniques Used in Stormwater Treatment Train WSUD Techniques