About Analysis-Driven Design

Drainage Design uses:

Rule-based design for spacing inlets and their offsets (see table below).
Road Slopes/Mannings coefficients and Intensity-Duration-Frequency (IDF) Rainfall coefficients for sizing pipes and grading their slopes to outfalls.
Rational Runoff calculations to analyze surface inlet performance and pipe run hydraulic performance.

For component roads, Drainage Design responds to contextual placement, slope and materials. Analysis of inlet location, tributary area, gutter spread and inlet performance utilizes both the component materials and the cross-slopes to adjust an inlet's placement and slope for the best solution in storm conditions. Analysis adjusts runoff coefficients to reflect the choice of materials used in a component road.

Drainage Design analysis enables you to change the AEP (Annual Exceedance Probability) setting (default = 1/10) prior to inspecting the performance of a selected pipe run. Thus, you can check its performance under different storm-level conditions.

With Inlet Analysis turned on (from an inlet's stack Tributary panel), Drainage Design re-calculates, in real time, runoff data for the tributary area associated with a pair of selected inlets. You can see the data change as you adjust the location of an inlet.

The following rule-based intervals and offsets are used when adding pavement drainage features:


Inlets	Inlets are placed only if the selected road uses a road style with a Curb track. Inlets are placed at low points along the road curb, spaced from high points based on the maximum inlet spacing defined in the Pavement Drainage design standard.
Manholes	Manholes are placed at inlet locations at offsets based on the horizontal and longitudinal placement offsets defined in the Pavement Drainage design standard. Horizontal placement offsets to the left are negative. Horizontal placements offsets to the right are positive.
Pipes	Drainage pipes are placed to connect inlets and manholes. Pipes are placed to meet the minimum defined slopes in the Pavement Drainage design standard. If the horizontal placement of a manhole is: Inside the roadway curb, pipes connect from each inlet to the manhole, then to the next manhole. Outside the roadway curb, pipes connect from one inlet to the next, and then to the manholes. Near the roadway curb, pipes connect between the inlets and then along the curb to the next inlet.