Coastal Inundation & Flood Risk Modeling: Sentinel-1 SAR Radar & DEMNAS Analysis for Jakarta Lowlands
Northern coastal districts of Jakarta face a dual threat: land subsidence (ranging between 2 to 10 cm per year) and High Astronomical Tides (HAT) compounded by seasonal monsoonal surge events.
In this HydroGIS risk analysis, we combined spaceborne radar sensing with high-resolution digital elevation models to map inundation extent and model future sea-level encroachment risks.
Remote Sensing Radar Pipeline & Elevation Stack
Because monsoonal flood events coincide with dense cloud cover, optical satellites (like Sentinel-2 or Landsat) are frequently blinded. We used Synthetic Aperture Radar (SAR) from Sentinel-1, which penetrates clouds and operates day or night:
- Sentinel-1 C-Band SAR (IW Mode): Vertical-Vertical (VV) and Vertical-Horizontal (VH) polarization backscatter coefficients ($\sigma^0$).
- Digital Elevation Model: Indonesia National DEM (DEMNAS 8m resolution) corrected for local tidal datum (Mean Sea Level).
- River & Canal Network: Ciliwung & Banjir Kanal Barat vector hydrography layers.
SAR Water Detection Principle
Smooth water surfaces act as specular reflectors, scattering radar pulses away from the satellite sensor and producing very low backscatter values ($\sigma^0 < -18 \text{ dB}$):
$$\Delta \sigma^0 = \sigma^0_{\text{flood}} - \sigma^0_{\text{baseline}}$$
Quantitative Risk Findings for North Jakarta
| Lowland Sub-District (Kecamatan) | Area Below Highest Tide (HAT) | Sentinel-1 Inundation Extent | Affected Population (Est.) |
|---|---|---|---|
| Penjaringan | 6.8 km² | 3.4 km² | ~42,500 Residents |
| Pademangan | 4.2 km² | 2.1 km² | ~28,100 Residents |
| Cilincing | 3.2 km² | 1.8 km² | ~19,400 Residents |
| Total Coastal Lowlands | 14.2 km² | 7.3 km² | ~90,000 Residents |
Spatial Infrastructure Recommendations
- Sea Wall Barrier Reinforcement: Priority 2.4 km sea wall alignment along Penjaringan waterfront districts.
- Automated Pump Station Siting: Positioning high-capacity drainage pump stations at hydraulic bottlenecks identified in the DEMNAS watershed flow accumulation model.
- Evacuation Route Signage: Mapping flood-free arterial routes to elevation nodes above +3.0m MSL.
Processed using SNAP (Sentinel Application Platform), QGIS HydroGIS, Python Rasterio, and WhiteboxTools.