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Network "nme" Flow line initiation below 0.004 square km flow accumulation, based on a 141cm resample of the topo-bathy surface. The more detailed east Marin County extent featured intensive hydrologic enforcement that had been derived from the storm drain systems of about a dozen municipal or county agencies. The analysis grid was resampled near 141cm gridding for precise 2-square-meter grid cells. Flow line initiation below 0.004 square km flow accumulation, nominally 1-acre catchment, was used to detect likely ephemeral flow over highly impermeable urban surfaces common in this area. In many cases, hydrologic enforcement had detailed curb gutters on both sides of the street at better than 1:1000 map scale. This much detail led to stability problems for the 32-bit Esri ArcGIS 10.3 for Desktop application over which ArcHydro was running, and so the east county area was produced in two parts. This "nme" network was named to imply "north Marin east". |