A 1 foot drop on a 100 run is only a 1% grade.

That's not much fall, and I'd be concerned that such a shallow grade could easily be negated, or in fact reversed by just a little settling of the ground.

Generally you don't want anything less than about 3% for natural drainage.

A reduced slope will also cause very slow water flow rates. If you are in an area with cold winters and or silty soil a 1% slope may not allow the water to run fast enough to adequately carry away silt buildups or prevent freezing of melt water.

Best of luck.

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