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Orange County moves to update stormwater design after consultants find rising short‑duration rainfall intensity
Summary
County staff and consultants told the Board of County Commissioners that short, intense rainstorms have become more frequent since about 2010 and recommended updating the intensity curves used to size pipes and drainage infrastructure; commissioners directed staff to draft ordinance changes and continue cross‑departmental resiliency work.
Orange County commissioners on April 22 directed staff to begin updating the county's stormwater design guidance after consultants said short, intense rainfall events have increased in frequency since about 2010, producing higher peak intensities that can overwhelm drainage pipes and rights of way.
The county's stormwater manager, Mike Drosik, introduced a study by CDM Smith that compared Orange County rainfall records, Water Management District gauges and NOAA datasets. Mitchell Heinemann, CDM Smith’s rainfall analyst, told the board the county's current guidance — based on a 1994 Orange County table and earlier National Weather Service charts — underestimates the peak 15‑minute and other short‑duration intensities that show up in recent years.
The change matters…
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