Principles and concepts in designing tropical-shore settlement in estuary ecosystem, case study: Weriagar District, Bintuni Bay

Weriagar District is located in estuary area and is prone to land loss, due to river and coastal erosion. This paper will describe about tropical-shore settlement design and house design in estuary area. The results from analysis phase shows that it's necessary to design a house and settlement that can fulfil the needs of indigenous people, both functionally and aesthetically. Functionally, the house is designed to provide spaces for both private and public needs of the family. It can be used either as a family private space or as a public gathering space between family and their neighbours. Aesthetically, house’ architectural form is designed into that identifies the locality of Weriagar District. The houses’ design feature highlighted in using local material, rainwater harvesting system, high pitched roof feature as response to hot-humid climate, and elevated-floor feature as response to tidal condition in estuary area. The houses design also considered daily activity pattern and community culture, including appropriate structure, construction, and material availability. The expected result was that the settlement improvement and house design would meet suitable standards and needs of inhabitants in Weriagar District.


Introduction
Weriagar District located in Bintuni Bay Regency, West Papua, Indonesia. Bordered by a river in the northern side and the sea in the southern side, Weriagar district is one of the tropical shore settlement in estuary area. The Tropical Shore Settlement Improvement Program was initiated as an effort to rehabilitate physical condition and life quality in Weriagar District. The Rehabilitate activities are to support and improve life quality of communities not only in Weriagar District but also in the Bintuni Bay and beyond by providing a reliable and selected resources. The Tropical Shore Settlement Improvement program scope includes House Design and Settlement Rearrangement, as well as Infrastructure Development. This program phase consists of Site Survey, Site Analysis, Concept Select Matrix, Value Improving Practices, and Detailed Engineering Design. This program was intended to obtain the house design that suits with convenience and functionality, but does not eliminate the architecture value both of function and aesthetics of the building. Infrastructure development program consist of improving and complementing the existing of public infrastructure and social facilities in accordance with the regional priorities of development in Weriagar District. The design and development in this program must be based on the ecology, aesthetic, function, and existing building conditions.  The water with high salinity enter into the bay and mix with low salinity water so it causes mixing between the fresh water masses and bay water stuck in the head of bay. This factor was the one that make it difficult in finding clean water. Based on the information gathered from the site survey, the water available is mostly infected with E. Coli bacteria and is overly salty. That condition of water is unsuitable to be used for daily purposes for the villagers in the Weriagar District Area. The infected clean water in this area is caused by contamination from waste water of the existing houses. At the moment, there are no waste water sanitation system available.

Green area and vegetation.
The riverbank areas and seaside that have the heaviest process of erosion and abrasion are those where the natural cover has been disturbed and that have become an open land. Nature can no longer be a supporting and inhibiting element of the rate of erosion due to the fact that local plants such as Nypa palm and mangrove forests have lost their media to be able to grow back naturally. Built environment especially in the dense area of the village have experience the most serious degradation in its environment and spatial quality with the decrease of green open spaces. These green open spaces are supposed to be inhibiting the rate of the tide that erodes the fertile soil layer on the wet land.

Building Materials.
The use of local materials becomes dominant because of limited availability of materials from the outside area and lack of supporting accessibility to send the material into the site. The local materials have been processed beforehand to ensure their strength, durability and to facilitate their maintenance. Local materials are used as structural elements of the building and as well as cover the walls of the building. Wood is the dominant material used in the existing buildings found in the Weriagar District Area. However, the fact that materials used in residential buildings are mainly unprocessed, local materials or raw materials indicate that the construction quality does not meet appropriateness standards especially those related to durability against weather condition.

Site plan design criteria
Some principles were used as consideration in arranging Weriagar District site plan [5]: a. Geographical conditions: such as water, soil and climate affect the engineering, design, and construction on the development area. To prevent soil erosion and abrasion in Weriagar District that often happened, it is necessary to make structural protection. The tidal conditions also have to be considered in the design of the building and walkway in Weriagar District. b. Image of Region: a visual image of character which captured when seeing a region to be maintained and created in the Weriagar District is natural and comfortable coastal village. c. Accessibility: Existing access in this area should be supported by improving its infrastructure.
Weriagar district can only be accessed via the water lane, especially the river. Therefore, the jetty boundaries that should not change, and the minimum number of resident remain the same. e. The building in this region is dominated by houses and public infrastructure. The building is generally a house on stilts made of wood material. Tidal condition affecting the floor level of the house and social facilites, as well as the surface level of walkway as public infrastructure. The highest tidal water level measured is approximately 1 m, therefore the floor level of the house and social facilities were designed above the tide level, approximately 1.5 m from the existing ground level. Meanwhile, the surface level of the walkway is 1.3 m from the existing ground. The distance between the new houses on either side is at least 6 m, and the distance to the front porch of the main walkway is at least 3 m. f. Landscape Arrangement is indispensable especially in the border areas of the river and coast area. The potential of erosion and abrasion is very high. g. Completeness infrastructure of region: Weriagar district as one administrative area in Bintuni Bay Regency, need to have regional infrastructure. Public infrastructure consists of a walkway, drainage, boat dock, and the Social Facilities were Sanggar Pemuda, Posyandu and a football field. h. Social and Cultural: Culture and habits of the local people should not be overlooked in settlement improvement program. There are many social and historical values that are embedded in their living that made a principle of life for the next generations, such as ceremonies when moving house, sacred house, do routine activity in the edge of the river and many other things. i. Regulation: The estuary area has a variety of restrictions or rules in size and complexity. Thus, in the arrangement Weriagar District need to consider regulation of river border, coastal border, and emphasizes the protection of the environment and restore natural function as an area that is always experiencing tidal conditions.

4.2.2.
House design criteria has some of point that must be suits with the site condition, such as:

Climate
The design creates a new identity that responds to its climate and context. The main purpose of building is to give its occupants comfort inside the building. The comfort parameters include [6]: (a) Natural Daylight and Heat Control; Natural lighting is what the design seeks the most. The building has to design not too wide so that the sun can reach into innermost room. Points to control are, the form of building mass; the pattern, position, and shape of building openings; the system of building's cover and shade control of building. (b) Air Circulation and Humidity Control; Good air circulation, especially inside the building, makes the occupants able to do the activity well. The more opening in the lower side of the building allows air to flow inside, while the opening in the upper side pulls the air below and get it out from the building. This air movement is the optimal condition of the building. Building design with modular system to accommodate typical functions is applied in every room of the house. Modular system is a way to keep the buildings in unity. The modular system leads to easiness in design and construction process. Open layout system allows function flexibility, adaptive to function, interior layout change, and easiness for development and expansion of building module and mass.

Design Character and Façade
Design character of the buildings gives the most impression about the character of the house itself. Vernacular character is contextual with local and cultural condition of Weriagar District.
The house design has to represent the local richness by applying it in the design elements.

Constructability
Another aspect that should be considered is the easiness in the building construction process. The building material has to be fixed in early design process. It will decide how large a space can be or how tall the building will be. The material should be surveyed to make sure its availability in the location. With large number of availability, the construction can be carried out using the same material to avoid social gap. The structural modular system is benefit guideline in the initial design process as well as each development.

Design Concept 4.3.1. Design Concept of Weriagar District Settlement Plan a. Housing Arrangement Concept
Based on the analysis of neighborhood space usage, community activities, and the layout of the existing building, as well as the structuring principle of settlement in estuary there are several concepts used in the arrangement of the house. Building Boundary Line Determination is based on security considerations, health, comfort, and harmony with the environment as well as the building height. b. Public Infrastructure Arrangement Concept The public infrastructure items in Weriagar District are Walkway, Drainage and Boat Dock. The arrangement of the new Walkway path follow the existing walkway path. Walkway path aims to connect each village in the Weriagar Disrict, ease for the people to access boat dock and jetty as the main transportation, and to anticipate tidal conditions. Drainage system arrangement aimed to speed up the flow of the tides and the flow of surface water to get out from the landside. Drainage was placed on one side of walkway to ease inspection. In drainage system, water flow that coming out from the site will be heading to the river. Arrangement of boat dock that serves as transportation infrastructure for small boat belonging to people who used daily both as a mode of transportation. Based on consideration to natural protection from abrasion and geobag protection from community activities, the river boundary line space will add 5 meters to 10 meters to plant Nypa palm. Based on national regulation that states the maximum building height is 15 meters and coastal boundary line is at least 100 meters, the site plan must be accommodated the 100meter border and then planted with mangroves. Mangroves planting is intended as one of the efforts to protect the beach from erosion [7].

Building Concept a. General Concept
Based on the analysis result of space usage preferences, inhabitant's activities, and existing house layout, the following recommendations on house layout are made, house layout should follow daily activity pattern, should follow room usage and function pattern that different from public buildings, should consider the building growth to anticipate additional room needs which have not been fulfilled in the initial house construction stage. The house shape and character should still be maintained while integrating original and additional parts [8].

b. Building Mass and Form
The concept of the building mass is to express the traditional aspect of Weriagar District local house. The building is adapted from the existing traditional house found in Weriagar District. One of the main identity of a Weriagar House is the elevated system of the house. The house floor is elevated at the maximum height of the water from the river located near the site, as a response to the swampy and wet soil condition. The elements which is adapted from the Weriagar District traditional house is the high-pitched roof. Not only to create the traditional expression of the house, but also to use natural ventilation system [9]. The roofing system was modified from the old traditional roofing system by adding vents at both sides of the roof. The purpose is to allow the trapped hot/warm air in the roof to flow through (crossing ventilation). The circulation of air in the roof will decrease the number of heat that received inside the house.
c. Zoning Zoning in the house designed based on function of space to anticipate the presence of space that has not been fulfilled at the early construction so the house character can still be maintained. The zones in the house divided into three zones, they are the public zone, the semi-public zone, and the private zone. The positioning of the zones is shown in the diagram above.
d. Air Circulation One design approach for the indigenous people in Weriagar District Area is the natural ventilation to provide good indoor environment quality. It maintains a healthy, comfortable, and productive indoor climate. Natural ventilation systems rely on pressure differences to move fresh air through buildings. The amount of ventilation will depend on the placement of openings in the building. Water Treatment Due to the site condition where the clean water supply system is still insufficient to the needs of the people, rain water harvesting is one of the solution applied in this housing design. The roof of the house was designed to tilt in four directions and completed with gutters in all four sides. The gutters will collect the rainwater which then be channelled into the water tank provided at the back of the house. The water tank is equipped with a filter system using a sheet of gauze placed on the openings of the water tank to ensure that the water that enters the water tank is free from dirt. By using the filter, the rain water held in the tank can directly be used for daily needs in the house.

f.
Natural Lighting Lighting is one of the most critical qualities of an indoor space. Exposure to natural light can be the solution to create a comfortable space inside the house. In Weriagar District Area, electricity is still limited. The indigenous people still relies on solar machine (genset) as the energy source. With that condition, natural lighting is one of the important concept to be used in this design. The diagram shows that the house design enables sunlight to enter the house easily as natural lighting. But the roof is designed wide enough to prevent the heat from the sun to enter in the middle of the day. This is intended to prevent the house users to feel overly heated during the day. Building Material Weriagar District is located in the remote area with difficult access, so the usage of materials both of component and systems structure using local material that are easily found on the location of the design will minimize the cost of shipping materials. The material must be processed beforehand so the quality of construction can fulfil the building standard of comfort and can be adapted with weather conditions in the region, and the material chosen is wood. Wood is the dominant material used in the existing buildings found in the Weriagar District Area.
h. Modular Structure System A modular structure is used as an approach to reduce cost (due to less customization and shorter learning time) and to offer flexibility in the house design. The module used in this housing design varies in the multiple of 1,50 m, 2,00 m, and 3,00 m. The smallest module used has the length of 1,50 m x 2,00 m. While the biggest module used has the length of 3,00 m x 3,00 m. The length of the module used is based on the availability of the material in the area.

Conclusion
Weriagar District is included into the category of settlement in the estuary area by its location in the coastal area that flanked by river and sea. By developing criteria and concept design based on resilient design principle and criteria, The Tropical Shore Settlement Improvement Program attempt to upgrading physical condition of Weriagar District and to support and improve quality of life of communities in the Bintuni Bay and beyond by providing a reliable and selected resources. Some of the design criteria for the settlements in the estuary area are divided into two concepts. Site plan concept that describes the fulfilment of criteria design used as consideration in structuring the site plan Weriagar District and the concept building based on analysis result of space usage preferences, inhabitant's activities, existing house layout and design criteria for buildings in estuary areas.