How to handle insufficient slope in stormwater pipes: Field construction experience

If the stormwater pipe slope is insufficient, it might drain okay in the short term, but problems will arise during heavy rain or after settlement. I once saw a parking lot drainage project where the pipes were buried and backfilled, only for the water test to reveal very slow flow at the end. We ended up having to partially excavate and redo it, which was much more expensive than just checking…