I've been assigned to do this grading project and it is becoming a challenge at least for me at this point. What is needed is top of Pond set to OG elevations, down 3.5:1 to a relative elevation of 5' then bottom infill. So far so good.
Now they want the bottom to funnel into a drainage inlet which is set at 368.55. Then they want the remainder of the pond bottom to all slope towards this inlet at about 0.5%.
SO what I figure I'll do is grade down the top the 3.5:1 at 5 feet deep. Explode the grading and take the bottom feature line and insert a low point near the drain inlet at el 368.55. Then I'll use the set grade/slope between points command and slope this featureline out at 0.5 percent to the extreme corners of the pond. Once that is set I'll do an infill and create a surface I'll call "bottom". Next I'll re-grade the top down the 3.5:1 only this time I'll target the bottom surface then do an infill to get one single grading.
Sound like a good way to tackle this? Before you answer take a look at the attached image and see what kind of animal I'm up against.
Yes I need to slope the entire spiderweb of a basin about 0.5% down so that all the water will drain to the discharge at elevation 368.55. Now it does not have to be exactly .5% I kind of figured I'd work out from the discharge a half percent north and south on the first (nearest) legs then continue on the remaining three legs.
Given that geometry I'd create some flowlines down the middle of each finger, all sloping from the outlet at 5%. Then I would apply gradings to the flowlines outward at some slope to make a nice pan for the fingers and make a target surface for the sides of the pond.
Thanks for the feedback Joe.
Thinking about it a bit more I realized that it would be better to not apply any gradings to the flowlines at all. Instead just grade from the top of the pond down to the relative elevation target and add the flowlines and infills for the bottom. That way all the parameters are met. Of course this will result in variable slopes between the bottom edges of the pond and the flowlines. The flowlines can be tweaked to compensate for excessive slopes.
For ponds I almost always use a dummy surface graded in all directions towards the outfall. In other words I set an elevation at my outfall and have a grading object that goes in all directions at the desired grade.
I then grade down to this surface with my pond top.
When we have a trickle channel say at point .5%, I will run a feature along the bottom then grade away from it at 2% well past extents of the pond.
Hope that helps.