Many times, a stream needs to be drained into a storm sewer system via a headwall. When this occurs, two analysis should be considered:

1. The headwater at the headwall (the mechanics of the water getting into the pipe at the headwall). Generally KYTC has utilized the hydraulic grade line (HGL) of the node immediately downstream of the headwall (or open ended pipe with no treatment) as the tailwater for a given event. In other words, the 10 year HGL for the downstream node would be used in the assessment of the 10 year headwater at the headwall/open pipe inlet.

2. The HGL from the storm sewer analysis should be evaluated at the headwall/open pipe inlet.

Sometimes these two numbers may coincide (usuall for shallow sloped storm sewer pipes where outlet control applies). However the two are techinically different analysis, and the higher of the two numbers should control how high the water level at the inlet is.

Since Headwater analysis is for culverts only, and HGL is for storm sewers only, it requires a series of switching the inlet pipe into the system from a culvert to a storm sewer pipe, and defining the tailwater in the culvert condition. It would be nice if these were seprately analyzed, and the Headwater was actually shown as a headwater.