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Hydraflow Hydrographs Extension: Critical Duration Analysis

Hydraflow Hydrographs Extension: Critical Duration Analysis

Hydrographs is a useful tool for its simplicity and (relatively) bug free performance, but the inability to integrate a "Critical Duration" analysis is highly limiting.


A Critical Duration involves routing a series of rainfall events with varying durations through the model and is required on a large percentage of projects involving stormwater management. The purpose of the analysis is to demonstrate the duration that would produce the highest peak flow and, thus, should govern design (i.e. 2-hour peak<6-hour peak>24-hour peak). The analysis could be performed for any recurrence interval, but the most typical in northeast Illinois is the 100-year (1%) event (IDOT-adjacent projects also require 10-year and 50-year). Durations range from 1-hour or less to 240-hour, typically.


Currently, the analysis can be performed in Hydrographs, but the process is quite cumbersome. If one wants to perform such an analysis, either a separate .gpw file must be created for each duration or the input for rainfall, duration, distribution, etc. must be revised each time the analysis is performed. Both options are far from ideal due to the amount of repetitive input. Most competitor software allows a Critical Duration to be performed within a single file. 


I recognize that this could involve some major changes to the software, but this is the biggest current limitation in Hydrographs. I look forward to this being incorporated at the earliest opportunity.



Robert Gilbert

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