Spatial dataset for the publication "A nationwide survey of drainage-ditch CH4 and CO2 emissions: within-system conditions, rather than soil type or land use, drive diffusive fluxes"

This dataset provides a national-scale inventory of drainage ditches and surface waters across the Netherlands, covering approximately 6143 km² of mapped water area. Of this, about 1322 km² falls within the 1.5–10 m median-width range, which represents the principal ditch-size class used in the associated national analysis. National area summaries by water type, source status, and width are provided in area_per_WaterType_status_width_med_m.csv and area_per_WaterType_status_width_class.csv. The dataset therefore provides a spatially explicit basis for quantifying Dutch drainage-ditch extent, upscaling greenhouse-gas emissions from inland waters, and supporting water-quality assessment, hydrological analysis, and regional water management. For rapid spatial visualization of the national dataset, an overview raster is provided as Waterways_NL_overview.tif. The dataset was developed for the studies "A nationwide survey of drainage ditch CH₄ and CO₂ emissions: within-system conditions, not soil type or land use, drive diffusive fluxes" and "Developing a spatial database for drained peatland forests in the North Sea–Baltic Sea Region". It combines existing hydrographic information from Dutch water authorities with additional drainage ditches detected from AHN5 airborne LiDAR data using the deep-learning workflow of Busarello et al. (2025). Existing water features are classified as Old, whereas additional LiDAR-derived ditch detections are classified as New. The complete spatial dataset is provided in Waterways_NL_dataset.zip. Within the 1.5–10 m median-width class, approximately 475 km² is associated with newly detected (New) watercourses and approximately 846 km² with existing (Old) hydrographic data, resulting in a substantial increase in the mapped extent of drainage ditches. Narrow watercourses with median widths below 1.5 m account for approximately 88 km². Wider canals, rivers, and other open waters account for approximately 2921 km², excluding the IJsselmeer and Markermeer. The mapped areas of the IJsselmeer and Markermeer are approximately 1130 km² and 683 km², respectively. These area estimates can be explored in the accompanying area summary by median width and area summary by width class. Water width was estimated from polygon geometry using rasterization, medial-axis skeletonization, and a Euclidean distance transform. Local width was calculated as twice the distance from the skeleton to the polygon boundary. The dataset contains median width, 10th and 90th percentiles, and width classes. For ditches, the mapped width represents the maximum ditch width at approximately surrounding ground-surface level and should not be interpreted as the width at mean ditch water level. The national distribution of mapped surface-water area across width classes is shown in Waterways_NL_histogram_width.png, or pdf. The figure distinguishes narrow "greppels", drainage ditches, canals/rivers, and wider rivers/lakes and separates existing (Old) from newly detected (New) water features. Soil type was assigned to the drainage ditches using the Grondsoortenkaart 2006, and groundwater salinity information was derived from the DANK008a groundwater salinization map. The spatial distribution of drainage ditches varies strongly among soil types. Within the principal 1.5–10 m ditch-width class, ditch surface-area density is highest on peat soils (7.51% of the total Dutch peat-soil area), followed by heavy clay (6.05%), peaty soil on sand (4.48%), light clay (4.01%), clay loam (3.73%), sandy clay loam (3.40%), sand (3.21%), built-up/other areas (2.38%), and loam (1.97%). These patterns are summarized in Ditch density.pdf. The national width distribution further shows that mapped ditch area is particularly concentrated in the approximately 2–5 m width classes, whereas wider canals, rivers, lakes, and other open waters increasingly dominate the larger width classes. The contribution of different soil types across the complete width distribution is shown in Waterways_NL_histogram_width_soiltype.pdf. The Zenodo deposit therefore contains the complete spatial dataset, national area-summary tables, tiled GeoPackage data with width attributes, auxiliary GIS files for loading and visualization, a national overview vertial polygon, and figures describing the national width distribution, soil-type distribution, and ditch surface-area density. These files can be used for national-scale analyses of drainage-ditch extent, surface-water area, width distributions, greenhouse-gas upscaling, hydrology, and biogeochemical cycling, and provide the source data underlying the national Dutch ditch and surface-water area estimates reported above.