February 26, 2025, Planning Board Special Meeting Transcript - WEHI

03/03/2025 06:36:47 AM Page 37 to 40 of 115 10 of 46 sheets 37 downstream. Because now the site isn't holding back1 water. It could actually be generating more runoff. So2 the issue with flooding downstream, now we're3 exacerbating that problem. If you develop this plan and4 now your producing even more runoff than less. The5 point of the regulation to reducing peak flow is that it6 should not impact further downstream. We don't want to7 -- in order to develop buildings you have to develop8 land sometimes, but you don't have to flood downstream9 areas.10 I'm going to be getting a little technical here,11 I just kind of want to use an analogy here to kind of12 make it simpler. Suppose -- I'm a basketball fan,13 suppose I saw someone dunk a basketball and say, yeah, I14 can dunk basketballs, then when you kind of went closer15 to the net and brought the tape measure to it you're16 like, wait a minute, this is an 8 foot tall net,17 basketball nets are 10 feet tall. And that's what's18 going to happen here. You're artificially shortening19 the time of concentration to meet these requirements,20 so.21 MR. KLEIN: Can I ask a question.22 I want to go a little further on --23 A. MR. KLEIN: One quick question. What year24 did that change? From using that general unpaved to --25 38 THE WITNESS: I don't know off the top of my1 head. I can get it for you. I don't know off the top2 of my head.3 MR. KLEIN: Do you know if, when they did4 the calculation that was correct at the time or you're5 sure it wasn't?6 THE WITNESS: No, I'm sure it wasn't.7 MR. KLEIN: Okay.8 MR. AFRAN: Mr. Chairman, I hate to burden9 to board, could I ask for a two-minute break.10 CHAIRMAN BAGOFF: You got it. Two-minute11 break.12 (Whereupon, a short recess is taken.)13 CHAIRMAN BAGOFF: Back on the record.14 Mr. Afran, Mr. Walsh.15 MR. AFRAN: Thank you, Mr. Chairman. I16 appreciate the break and we will continue with Mr.17 Walsh.18 All right. So we just finished talking about how19 A. the time of concentration was used with the current20 method. It's longer, which means the flow rates should21 be lower than originally calculated in the applicants22 submission.23 I want to point something out with POA-2 here.24 You can see the blue line here, this is where you show25 39 the flow path of POA-1. This is a path that goes from1 top of the drainage area down to the bottom.2 You're tracing a line that's

-2 here.24 You can see the blue line here, this is where you show25 39 the flow path of POA-1. This is a path that goes from1 top of the drainage area down to the bottom.2 You're tracing a line that's parallel to those3 Q. red arrows, is that correct?4 Yes, parallel to the red arrows.5 A. You'll see there, that path total is about 6716 feet long. What's unusual here is you compare it to the7 other model of the drainage area, the left POA-1, the8 blue line goes all the way to the discharge point, which9 is what it's supposed to do. But for some reason they10 stopped it short, it stops here, but the drainage -- the11 discharge point is here. The time of concentration is12 supposed to measure the entire flow event. This water13 should keep going down here, go around, keep going. At14 a minimum it's 700 feet short. So there's 700 feet of15 flow, this isn't accounting for the time of16 concentration calculation. And, again, this is just17 another example of how like a basketball rim gets18 artificially shortened, because now it's traveling less19 distance than it really is. So again, time of20 concentration will be, will be shorter. The peak flows21 will be higher and it will be easier --22 MR. AFRAN: For the record, the battery was23 running low on Mr. Walsh's computer and he's about to24 charge it.25 40 All right. Sorry about that.1 A. So once again, this is just another example how2 the time of concentration calculation, it's not even3 complete here. They use their own method and not using4 equal distance, so it just can't be trusted.5 So let me ask one question. Accepting what you6 Q. just said, what does this translate into in terms of7 practical outcomes that the board should be concerned8 about?9 So to demonstrate that what I did was, we used10 A. the information that was available from the applicants11 submission. We recalculated the existing conditions12 models using the HydroCAD, which is the model they used,13 to develop new peak flow runoff rates, and compare them14 to what they hd in the report to see how big a15 difference is, because this is their own methods. It's16 less than half the distance. We were concerned what the17 impacts of that's going to be.18 I got to go through my notes to make sure I get19 the numbers correct.20 So the applicant's submission shows that time of21 concentration is 16.8 minutes. Our calculation is22 closer to 60, at

o be.18 I got to go through my notes to make sure I get19 the numbers correct.20 So the applicant's submission shows that time of21 concentration is 16.8 minutes. Our calculation is22 closer to 60, at about 60.8 minutes. Four times longer23 more time during that time period.24 Now, for example, two-year storm we calculated25