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Global warming resulting in climate change has become a new disaster in the world. One of the changes in climate is the rise of sea water to land surface, which causes tidal flooding. One area that experienced tidal flooding was Kawunganten District, Cilacap, Central Java Province. The area is traversed by the Parit River with the river estuary located in Ujungmanik Village. The problem of tidal flooding in Kawunganten District can be overcome by constructing a moveable weir in the estuary of the Parit River. In planning on the moveable weir, a hydrological analysis is needed to determine the flood discharge plan. Rainfall data used as a basis for calculation of flood discharge at the study site is rainfall data from 3 observation stations namely Cilacap Station, Majenang Station and Ujungbarang Station with the recording period from 2009 to 2018. Calculation of rainfall plan is done using the Pearson Log Method III with a value of T100 = 165.463 mm. The results of the calculation of the flood discharge plan with the haspers method Q100 = 280.989 m3/sec, while the weduwen method Q100 = 132.804 m3/sec and the HSS Nakayasu method Q100 = 102.444. Furthermore, an analysis of tides on the coast of Cilacap Regency with the results of MWL (Mean Water Level) = 110 cm, LWL (Low Water Level) = 20 cm, HWL (High Water Level) = 220 cm.

In Semarang urban coastal areas experience daily flooding from the sea during high tide (tidal flooding). Flourishing residential areas have changed into unhealthy slums with the nuisance of daily flooding in parts of the city. To overcome these problems a polder system was implemented to address the tidal flooding. The Semarang polder system is the first fully operational polder system in a densely populated urban area in Indonesia. This article describes the polder system that prevents flooding in the Eastern part of the city; the Banger polder area. An important element of the polder system is an emergency response plan that prepares for a flood emergency condition. The emergency response plan provides different emergency scenarios and identifies emergency levels and criteria. The management of emergency situations can be divided into four phases, namely mitigation, preparedness, response and recovery. The research results provide a detailed description of four emergency scenarios with 3 emergency levels for each scenario in the Banger polder area. The scenarios are; pumping stations operational damage, high-intensity rainfall in combination with high tide, failure of levees and dams, and an inflow of water from the west and east side of Polder system area.

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The high demand for land to be built on, makes the price of land more expensive. Various efforts were made to get land to build houses on, one of them was by way of coastal reclamation. The pond area initially functioned as a water catchment area, but later became new land through the reclamation process. This will have adverse impacts on the environment such as flooding due to lack of water storage. To overcome the problem of building in the coastal area without reclaiming, is using floating house. A floating house is a building structure that floats on the water surface by leaning to drowned area weight as the weight parameter which the structure could handle. This research is done to analyze the material platform. PVC pipe is used with floating force (Fa) parameter and cost plan analysis. The structure weight analysis total result is 555,887.5 Newton. The floating force of structure platform is 648.792 Newton. The connection system is a bolt connection system that us 3 cm in diameter with an anchor of length 22 cm, and a total of 4 bolts on each connection. Cost plan analysis using PVC pipe costs IDR 379.500.000,00.

Cilacap is one of the regions in Indonesia in the southern coastal region bordering the Indonesian Ocean. In the coastal areas of Cilacap including Kawunganten district, there are frequent floods due to sea level rise. Tidal flood problem in Cilacap can be overcome by constructing a moveable dam. The selection of moveable dam gateis needed so that it can be work optimally. Data in this study were obtained through a questionnaire and distributed to respondents who were experts in the field of water. There are 5 criteria used to select the type of moveable dam gate, namely material, function, operational and maintenance, cost and location. There are 4 alternatives of moveable dam gatenamely flap gate, radial gate, sliding gate and rubber dam. The results of the questionnaire were then processed using Analytical Hierarchy Process. The results showed that the most important criteria to select the type of moveable dam gate is cost (0.273). The best alternative of moveable dam gate based on all criteria is flap gate (0.291). Movable dam with flap gate became the priority because it is easy to operate and low cost. The best location for moveable dam placement is before Ujungmanik Bridge with a score 0.376.

The impact of tidal floods in the coastal area of Semarang greatly disrupts people’s activities and damages settlements and infrastructure buildings. Floating building is one of the alternative solutions to overcome the rising sea level. This study aims to compare 2 (two) floating housing material platforms, namely EPS (Expanded Polystyrene) and PVC (PolyVinyl Chloride). The analysis method of floating structure platform was carried out by using various indicators, namely, the uplift generated, the stability and costs. Based on the findings of the analysis, the uplift platform to bear building loads on the water surface showed a value of 0.2 ton / rod for Ø10 inches PVC pipes and 4 meters in length. Then, the uplift capacity of 0.9 tons / sheet was for EPS Styrofoam with dimensions of 2 m x 1 m x 0.5 m. The stability level of floating buildings on water was indicated by the high value of spectrum that was +3.23 m for PVC and +3.61 m for EPS. To support the loads of 54.01 tons, the comparison of material expenses and installation of PVC materials required a cost of IDR. 561, 561, 350.00; meanwhile EPS material cost IDR. 40, 420, 000.00.

Floating building is one of the solutions to anticipate residential areas against Tidal floods which have been occurring on the North Coast of Central Java. This floating building can adjust its buoyancy to the effect of rising sea level and land subsidence. This building can be applied in sea tidal flood areas and retention ponds in polder systems. The main materials used as the floating building platform are styrofoam and lightweight concrete. This study aims to determine the stability, capacity and buoyancy of the prototype platform using styrofoam and lightweight concrete. This study uses mathematical analysis methods and prototype testing with laboratory experiments. Based on the analysis result for the styrofoam material platform with dimensions of 2 × 2 × 0.62 m, a buoyancy force of 2.73 tons was obtained with the Safety Factor (SF) of 1.25. A lightweight concrete weight of 0.97 tons, the load that can be supported by the prototype is 1.2 tons. The prototype of the styrofoam material platform with a lightweight concrete cover has a stable condition with a value of m>0, namely the center of object weight (B0) is +0.74 meters and the metacentric value is +0.9 meters.