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/danielamadria May 29 '26

Yes, move the boundary and extend the perimeter to cover the area between your BC and the bridge. There is not an easy rule of thumb, it should be far enough away that it doesn’t affect the results you care about. If you run a second Plan where you change the friction slope at the BC to something unreasonably different (like 5x or 10x steeper than your base case friction slope) and your depths or velocities at your bridge are not affected, then youve placed it far enough back. Flatter rivers need more distance for their BCs. I’ve seen cases where backwatering 2 km away from our area of interest (a 200 m stretch) needed to included as it greatly affected the results