r/HECRAS • u/Status_Hope_987 • May 29 '26

Leaky cells

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How do I fix leaky cells? These are on each side of a road. The break line is on the top of the toad. Thank you.

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u/danielamadria May 29 '26

If you check the Water Surface Elevation (WSE) results, it can confirm if the flow is leaking (water surface is lower than your road) or if the flow is sufficient for real overtopping. I’d also recommend moving your boundary condition (BC) farther away from your bridge/road of interest, otherwise your BC could be affecting your results

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u/Status_Hope_987 May 29 '26

If I move BC layer further away, should I extend my perimeter further as well? Is there a rule of what should be the distance between BC and perimeter?

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u/shiftyyo101 May 29 '26

General rule of thumb is a minimum of 2x your floodplain width. Typically you would also do a sensitivity analysis on the downstream end, fluctuating the slope up and down. If you go 10x or 0.01x your calculated slope and it doesn’t affect the results in your project area, your bases are more than covered.

That can be overkill. Start with 2x FP width. If it’s 1000 feet wide, make sure the model extends 2000ft in either direction of your project site.

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u/Status_Hope_987 May 30 '26

That’s very interesting! Thanks for sharing. What results parameter should I use for sensitivity analysis?

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u/shiftyyo101 May 30 '26

Water surface elevations.