Tips, QA, troubleshooting

Common QA checks

• Units sanity: area in ha vs \(km^2\), lengths in m, Tc in minutes.
• IDF sanity: intensities should typically decrease with increasing duration.
• Return periods: peaks should typically increase with return period.
• Method selection: verify Rational vs SCS threshold behavior for each catchment.

Typical issues and fixes

Peaks look too high/low

• Verify \(T_c\) method inputs (flowpath length and elevation difference).
• Verify the IDF row and the intensity segment used for the duration.
• Verify ARF is applied (or not) as intended.

Channel sizing does not converge / unstable depths

• Check slope sign and magnitude.
• Check Manning \(n\) is reasonable for the selected material.
• Ensure geometry constraints are not forcing impossible flow conditions.

Culvert results are unexpected

• Confirm geometry, slope, length, and inlet condition assumptions.
• Confirm whether inlet vs outlet control is governing and why.
• Review outlet velocity and any protection sizing assumptions.