City of Charleston SC Charleston City Plan, 28 Sep 2020

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From YouTube: Special Planning Commission Meeting: City Plan 9/28/20

Description

Agenda:
Engagement Updates
Water and Land Use Analysis
Public Comment

View engagement update slides here: https://www.charleston-sc.gov/DocumentCenter/View/27688/Special-PC-Meeting-Slides-Sep-28-2020
View water and land use analysis slides here: https://www.charleston-sc.gov/DocumentCenter/View/27685/Sep-28-2020-Special-PC-Meeting-Slides---Water-Analysis

A

Hello, everybody.

B

Hey there, how are you, hello,.

A

A

This has been is not being actually on time.

A

I didn't hear you angie, I saw your lips move, I don't know I mean I know angie and I are like rushing in and carol you were just I mean donna you're there. Just all the time. I mean it's crazy. You were you probably already looked at that video. We were supposed to see to enlighten ourselves right.

C

Well, I've actually been at all the engagement meetings, so I mean that's that's what I did with plan west ashley. You know, so I just committed myself to this. Also.

A

Well, good: well, we rely on that for sure.

C

um But I think we're getting an update from the water people and they've.

A

C

They have done some incredible work, it's it's! It's pretty! It's! It's dense and good, very good.

A

So that's our presentation today right, I guess that's not sad.

C

I believe so, plus some community engagement updates, probably that's correct.

A

I can't see everybody.

A

I can only see four of us when things is that true with everybody can y'all only see four when you have the planning.

C

Yeah, but you might be able to sometimes I can.

B

A

B

Day, I can see eight, so you can stretch it out or go to grid view. If you want to see everyone.

A

Go to what kind of view.

B

A

Go to the grid.

B

View you can read it.

A

Okay, I just need to go. Do that one, I'm not okay, great view.

C

Now, there's a gray line sunday between the presentation and all the people and if you can grab hold of that, you can make that presentation screen smaller by moving it to the left and you'll pull out. You pull up more people.

A

Well, I'm on my ipad. Oh.

C

A

That's that's kind of different yeah. I know my um my laptop doesn't work real well with um with this, so I think that's probably the extent of what I can do on my.

B

B

Y'all, I'm gonna excuse myself for a minute while we're getting set up. Okay, chloe I'll, be right.

A

Back I can tell charlie he could take off his past now, hey harry. I just got to see.

A

D

Chris, I'm ready whenever you all. Are you just? Let me know.

E

We're ready, charlie.

D

Okay is chris uh kristen's place or.

F

D

Okay, all right we'll go ahead. um This is a special meeting of the city of charleston planning, commission we're going to get updates on on the city plan and meetings that have been happening uh in regard to that.

D

So uh I'm going to turn it over to mr morgan, we'll introduce any staff members who participate and uh kind of lead us through this.

F

All right well, thank you, mr chairman, so um uh just a super simple agenda today, although some uh on the number two item, we definitely have uh extensive update, but uh first off we're gonna have a city plan, engagement, update from chloe stuber about what we've been doing over the last four or five weeks meeting with various parties and getting input on the plan and then the second part is our city plan.

F

Water and land use analysis update of where that team is with their analysis, and it's some very detailed, very interesting information that I hope you all listen carefully to and have lots of questions for the team on, because I think there's a lot that we can learn from that, and this is really going to be the basis of all of our land use recommendations in this planned document.

F

So with that, I think I'll hand it over to chloe stewber our planner who's. Gonna. Give you background on our engagement updates.

E

Hey everyone. Can you hear me all.

D

Right, yes, yes, ma'am, fine,.

E

E

Okay, so I'm gonna go through this pretty quickly and just stop me if you have any questions I'll be watching the participant window, if you use your raise, handle I'll stop so just some quick overview updates by the numbers we've had over 300 participants in our virtual listening sessions, we've gotten to all areas of the city except james island, which is happening tomorrow, and we've had three housing labs, two water labs and two open listening sessions.

E

We are support, providing support to groups and individuals to host their own meetings and have ten and counting so far confirmed several more tentative and we hope to recruit some more. In the coming weeks.

E

We've had almost 900 survey responses collected, I think, probably by the end of the day, will be at 900, if not above that, 750 flyers distributed. That includes some census. Flyers. We've been tagged teaming with census and voter registration efforts and helping to get the word out about all three things and then 300 postcards distributed, which the postcards are basically just a mixture between a flyer and a business card for the city plan, inviting with several invitations on there to get involved. So on the right here. Are some group photos from our various listening sessions?

E

This is a fun way that we've been closing out. Those meetings and the so far wes ashley has won the challenge um we'll see if james island can beat west ashley's numbers has had west ashley's had the highest attendance uh so much so that on our evening listening session, we had to do two group photos because we couldn't fit them all to one screen.

D

I see miss jacob's smile on so she must be happy about that.

E

Yeah, yes, uh miss jacobs is our honorary um staff. Member has been in every single one of the listening sessions so far, um okay, so this is where we are in the engagement schedule in terms of the activities that we have confirmed so far, so we launched in august. That's when the listening sessions began, those continued into this month september september, we launched our survey and that's also when community-led meetings. That's when we got our toolkit out and people started scheduling those going into october, we'll wrap up our listening sessions.

E

Our last one is october 5th, we'll continue doing outreach for the survey and continue providing support to community-led meetings.

E

1St is when we wrap up this stage of engagement so november. 1St is when we'll close the survey, and that's also when the notes from the community-led meetings are due early 2021 next year. That's when we will resume our uh next phase of engagement that will be centered around reviewing the draft plan. Those activities and dates are to be determined, so this is a list of all community-led meeting hosts that have that we've confirmed with so there are more, as I mentioned earlier, that are tentative um and more that we hope to recruit.

E

But these are the ones so far that have confirmed not going to read through all of these, but, as you can see, it's a good mixture of groups that are in touch with a diverse mix of our population.

E

So we're hoping that these will be a great supplement to the city-hosted meetings in terms of reaching our goals of diversity and.

E

Coverage of the city- and uh this is my last slide- this is just a uh a list of our upcoming meetings, so these are the city hosted meetings that are taking place this week's this week and next, and that will wrap up our virtual meeting schedule.

D

Well, have you all been happy with the uh with the participation? I don't know if y'all anticipated a certain amount or.

F

I I think that you know the fact that we're in the middle of this pandemic and and it's you know every one of these has been a completely virtual meeting. I mean there have been some liars going around and stuff like that to people, but um I think that um it's it's been a good turnout, it's incredibly difficult, but to get participation you know. But but if you look at where we were with our plan 10 years ago, I think we've had probably comparable attendance.

F

It's probably taken a lot more staff time to get to where we are this year than it was 10 years ago, just because of the again the nature of how we do these and that we're doing more meetings, but I think we at least have equaled the type of participation we had before and the other thing to remember with a plan, is it's always more difficult to get people to participate when they don't have something to react to?

F

And I think, by virtue of us saying that we're going to let the public again have another round of input when we've got a draft of the plan and then they can see, you know they can see what's being recommended for james island or they can see what's being recommended for the upper peninsula or whatever. I think we'll get more participation then, and we may be at a point with the pandemic, that we can have some in-person sessions by then too. So we'll see.

D

Thank you, christopher.

E

And miss jacobs has her hand raised.

C

The distribution of the flyers and the postcards: what was the expected outcome of that was that to get people to be aware of zoo meetings or to send in a survey, what exactly were those? What's the target targeted result for those.

E

Yeah, the flyers were specific to uh coming listening sessions and the postcards were are more general get involved, so they have the three invitations on those are register for an upcoming meeting host your own meeting and take the survey. So that's more directing people to the website providing contact information for the plan um and just getting people's attention so do.

C

You all have any way of analyzing a metric on whether that was successful or not, and getting more people involved. Is there any way of tracking the success of that.

E

Yes, in the well, the only way we have that right now is with the survey we can see when people take the survey. The last question is: how did you find out about this? Okay and one of the options is flyers or postcards, and so we can see that some people, um some people- have responded with that as being how they found out. But I, the vast majority has been through social media cool.

C

Okay, thank you.

D

Thank you any other questions, if not uh christopher or chloe. What's next.

F

If I could just add that chloe and our consultants, our engagement consultants, have just been doing a phenomenal job and our whole staff has too, but chloe's really cheering this up and it's it's again very difficult work in the environment, we're in but they've been doing a phenomenal job with it.

D

We we appreciate it and understand that you'll have to a lot of obstacles to deal with with this pandemic. So thank you. Chris.

C

And I'll echo that since I've been at these meetings there, there has been some diversity at these meetings. I've been I've been impressed with that and some young people and some really good thoughts and some consistent trains of thoughts. So that's been good to see.

D

All right, chris, what's next.

F

Okay, well, I'm going to introduce andy stenard with the wagner and ball firm. That is going to talk a little bit about uh our water and land, use, analysis and kind of show you all what has been presented uh in our water labs that we had last week. I guess- um and so those of you who may have seen some of that- you may see some of the same things, but we want we.

F

We felt this was so important to this plan that it was worth devoting most of one of your special meetings here to this information and letting you all, you know, digest it and ask as many questions as you want- and you know talk here essentially one-on-one with andy about what they're finding. So, um with that I'll hand it over to andy.

G

All right, thank you very much good afternoon. My name is andy stern, head with wagon bowl architecture, environment in new orleans, and um thank you for the chance to talk to you again today, good to see all of you again.

G

I apologize at the beginning, there's some very vigorous lawn care happening outside. So if you hear a little background noise, that might be what it is. um This is exactly the same presentation that we gave twice at the two water labs on wednesday last week. So I'll speed it up a little bit from uh from that presentation. But but please do stop me if you have any questions or chloe someone stop me. If you see any hands raised and I'd be happy to elaborate more, um I'm gonna go ahead and skip through this city's introduction.

G

Here I think you all are familiar with what the city plan is then I'll get to the good stuff.

G

So the purpose of this presentation, it was meant to be more technical in nature and give an overview of the of the types of analyses we're doing and some of the preliminary results. So this is all still draft and work in progress, and it is has an eye towards public presentation. But these materials were not specifically designed for public presentation, so they're all they're, all a little more technical, I think than than would normally be presented in a format like this.

G

That's something we will be working with the city going forward to tweak a little bit how we best communicate some of these ideas, but this was the first really the first slide or jacob's. Last slide before we started on wednesday to introduce kind of a four-part approach going forward. But there might be certain parts of the city that will be defended against sea level, rising uh water and water of other types.

G

Some parts of the city that can adapt or that will need to adapt and whether that's housing structures, roads and infrastructure parts of the city that should be reserved for sea level, rise and and for water in nature and some of the natural marshland assets and upload forest even and then growth. Some of the which parts of the city are most suitable for safe growth and for for continued, perhaps densification.

G

um So this is kind of an early working framework to organize some of the ideas.

G

So we began with our team. uh Most of the presentation last week was uh given by wagner and ball, but we had participants from all the other teams, especially some key insight from josh, robinson and aaron stevens at circulate our two locals and dale morris at water institute of the gulf.

G

So again I'm going to go a little faster than normal just to get through. Some of these ideas um I'd be happy to discuss anything in more detail, but um I think this will be about 15 minutes or so um so the land and water analysis really is building on the dutch dialogues work from last year.

G

The really the previous two years, beginning with that base layer of ground- and this is really how the city teed up our analysis as well, that this land and water work would ground a lot of the other decision making layered on top, so we're taking what we did in the specific dutch dialogues focus areas applying that more broadly across the rest of the city and and then going a little bit more in depth.

G

We've done our own uh specific engagement in addition to the city and have spoken with all of these people in different various different formats, including some key elected officials.

G

This also is ongoing and we're happy to continue conversations as needed or, as others are interested, but we've really gotten some key feedback, especially from these regional stakeholders and elected officials, about what might be possible different recommendations.

G

So the next couple slides are about the water context, the types of flooding and what kind of setting the parameters for our analysis first being rainfall, and this is a noaa data set and what was what we're seeing just something to highlight it from other cities in the country. Is that what is considered the 500-year rainfall today is becoming the 100-year rainfall?

G

That's not necessarily true in charleston one-to-one, but that's a trend that we're seeing elsewhere- and I know the stormwater manual anticipates 10 increase in uh rainfall intensity, but there might be a need to even bump that up or revisit that that parameter over time.

G

But it's a lot of water 20 24 hour 100 year, storm 10, inches of water. It's a lot to deal with.

G

Another water context to sea level rise so we're using as the basis for our analysis the intermediate noaa scenario, which is the same as what the city used for its sea level rise strategy and that's, aiming at a range of two to three feet of sea level rise, 50 years out in 2070, and of course this is a range, could change and should be revisited over time, but um so we're looking for comp plan purposes out to about a foot of rise, just shy of a foot. But again it's a range should be taken.

G

Longer view should be taken here for length of mortgages, service, life of buildings and infrastructure. The decisions made made now obviously have a much longer tail of impact.

G

Storm surge, another key water context, factor in the map in yellow. You see there kind of a worst case, category three storm surge as if the worst case were applied across the coast.

G

So, that's just to say, there are different types of storm surge impacts that we can model, whether it's this worst case scenario, which is the the noaa 100-year storm that was called the slosh model or the storm surge incorporated in the fema floodplain, the regulatory floodplain, which is a little bit less intense, but we've looked at both and I'll, get into that in a little more detail, so trying to define what the flood means, because it changes depending on where you are water.

G

Elevation depth mean different things and different things in time, so we're trying to establish what what defines the flood is. It is it keeping water out of your home or business. Is it what's required to maintain safe egress?

G

What emergency access and then kind of hinting here, anticipating a future adaptability future, that's more adaptable with building types that can change over time, foundations and structures that might be able to be elevated.

G

So now a whole bunch of maps we've taken a watershed approach for this analysis.

G

So what you see here in gray and dark gray, is this city of charleston a boundary and in dashed black, you see the ugb tracking around what we've what we've done is defined the new boundary for our analysis, the purple line outer purple line here and that's capturing all of the of the smaller urban watersheds that affect city property, so any any water potentially flowing within, with the exception of one or two watersheds. These outer lying some of these far outlying just kept john's island whole.

G

But basically, this boundary is defined by all of the water that that might impact city property, whether that's from tide or rainfall, and even if that's just a little bit um and of course water doesn't follow the same political boundaries. So we tried to find the geographic extent made the most sense for our analysis and those watersheds are defined in large in large part by topography.

G

So um you all are, I'm sure, are familiar with this already, but the aspects of cainhoy rise all the way up above 30 feet, even in some localized portions, here, 40 or 50 feet above sea level, but most of the most of the city elevation we're dealing with is in the 10 to 20 foot range or so and again these lighter purple lines in between you start to see the watersheds I'll get into that in a little more zoomed zoomed in detail, and so now you see the watershed itself. This is the in light. Blue.

G

The light blue fill is the fema 100 year floodplain. So that's the one percent chance of flooding any given year from a combination of tide rainfall or surge as fema defines it and one other data point within the flood plain. Is this ve zone potential for higher velocity water or waves from storm surge? And you see you see those darker gray zones kind of in these perimeter locations around the city might be exposed to a little bit more risk um here.

G

Also, you see that we're breaking down the city into more or less the same chunks that were used in the vulnerability analysis in our inner and outer west ashley distinguished here in the daniel island from kane hoy, but that's allowed us to use the vulnerability analysis as a as a basis, even though that was defined by census, tracts and here we're using watersheds. The data has really grounded given us a huge leg up head start, um so we're building we're building on that. That past work really excellent work by fern leaf that the city commissioned.

G

So now, just around the city zooming in a little bit, I'm not going to get into any more resolution than this the rest of the presentation, just because it's so broad. This is kind of an introductory scope. But ultimately our analysis will zoom in a little bit more than this with each of these focus areas with the all the accompanying maps and analysis. But I think what to focus on here. Is these inner purple lines? Give you a sense of the scale of watersheds in different parts of the city, all the way from church creek?

G

Here, one of the larger ones to some of the smaller urban watersheds in west ashley, another big one to focus on is james island, creek, defining water feature james island.

G

Moving around to john's island- and you see how the scale of some of these starts to stretch out kind of with the parallel high ground, the old dune ridges.

G

We'll get into a little bit more later on about how to think about the different types of watersheds and what that might mean for land use recommendations.

G

So here moving into a little bit more of flood plain analysis, the land and the floodplain isn't all the same.

G

So what this map is showing in green is the fema flood plain 100 year, flood plain and in in orange, the additional area that is subject to storm surge flooding outside of the flood plain according to the noaa slash model, category three kind of worst case scenario.

G

So you see that almost all of the city and much of the region is is potentially impacted by flooding, but that could be to to various depths. That could mean anything from six inches to a foot or or more far, more sometimes along the coast, and so we'll pull this apart. A little bit um just remember the green and the orange um so that green range um really captures all these different types of flooding.

G

This is just a prototypical standard, cross-section through charleston landscape, from the coastal edge to the flood plain itself to the upland condition, and you can see the different types of flooding that might be experienced across the city as you move down the slope so upland, not a lot of flooding you're outside of the flood plain, with a trend for better soils for infiltration, some of these old dune sand, ridges that let water down into the soil.

G

We can take advantage of that for reducing runoff downslope, but that rainfall builds up at low points and ponding and, at some point starts to interact with the tide coming up. So you have a you, have points across the city with this compound flooding, where tide and rain interact and then layered on top. Is this range of storm surge? That might happen less frequently, but with more severe impacts.

G

So pulling apart, those floodplain and storm surge water levels a little bit more. This is an analysis of the land elevations within those orange and green shapes. So all of the flood plain is not at the same land.

G

Surface elevation, there's actually a range starting from about nine or ten feet, all the way up to 15 to 16 feet, and that indicates that compound flood risk, so you'll have more of a tidal risk at the low end of the flood plain more of a rainfall risk at the higher elevations within the flood plain, and then you've got this gradient in between where those two things interact and then the storm surge risk piling on top at different elevations, all the way up to even 20 25 feet in a worst case,.

G

And that's this is this: is land elevation, so you might, you might be experiencing worst case, storm surge, even even up to some of those higher levels in certain parts of the city, not not everywhere.

G

Okay, so now a little bit of analysis about the land elevations and the the amount of land at certain elevations across the city. So you see um this is this is not a percentage basis across the bottom. This is actually square miles, but we have we can. We can show another breakdown in percentage, but if you just squint at it, what you see is there's a small percentage of land.

G

That's high up, there's a much larger most of the city occurs between you know, five, six, seven feet and fifteen feet or so, and then a little bit of land here down at the end within the title range, and one of the goals of our analysis is to map these critical thresholds across the city so trying to define where different kinds of risks occur, at which elevations across the city and then taking those critical elevation thresholds and applying them to land use recommendations.

G

So you see this recognized. Eight foot uh mean lower low water, major tidal flood elevation, the tidal flood risk is kind of happening currently up to about eight feet. Then you'll get this. This compound flood risk, where you have water, coming down the slope and tide coming up, so there's this compound risk in between a little bit of rainfall, risk above and then relatively safe, ground, long-term, safe ground above that and we've mapped the percentage of of those land surface elevations, subject to each of those types of risk.

G

So, for example, in this teal green color, you see what percentage of land, let's say: 10 feet you get about: 40 percent somewhere somewhere between uh call it. I don't know. 40 50 percent in between of the land at 10 feet uh is, is within the floodplain within the 100-year floodplain.

G

This is a little bit complicated to read and really should take more time to explain this and study it, but I'll keep moving. Just for the sake of the presentation and again we haven't identified specifically what these levels are, but that's one of their goals. It's one of our expected outcomes.

G

If you, if you think back, if you remember it all to some of the johns island recommendations from the dutch dialogues, we had similar elevation ranges that guided certain types of recommended land use. So we're revisiting that methodology here and refining a bit this everything I've showed so far is an average over the whole city. This analysis has also been conducted per focus area and some of these levels change slightly based on local topography and water impacts.

G

And so back to those four key strategies, you see how they sort of play out sort of farmer logic in a way reserve the low ground for water defend in certain places and adapt in others in this mid-range and then in the higher elevations. Here, try to focus future growth or reinvestment and retrofits.

G

This is hinting now at some of those specific land areas for each of the focus areas across town. This is just layering them all up. Think what you see is this canehoy gray portion sticks out. That's to that indicates um there's a there's, a larger area of land in canehoy at high elevation. It's kind of that high ridge, um part of the francis marion forest part of the undeveloped area up above king hoy, and you see john's island- has some relatively high ground as well.

G

The rest of the city falls in this more or less in this middle range. James island tending to be more of the low ground. In fact,.

G

So what does that look like on a map, so this map is trying to capture a first pass of where that compound flood risk range occurs. So we've got the the title: the high tide influence um and then the that compound risk, and then the lighter blue.

G

This may be mis mislabeled, in fact, but then the lighter blue is the the more of the rainfall risk in the higher elevations.

G

So um you can see where that's where that risk is kind of creeping up, the floodplain based on the tidal creeks and then what happens if we project three feet of sea level rise on top, so this is the city's maximum projection for 2070 and how that changes.

G

These maps are a bit hard to read at the regional scale like this, but it's easier to see when we zoom in again coming coming future, not this presentation.

G

Okay, so a little visual breather here, a lot of dense information, um transitioning now from the big regional scale to sort of a watershed scale. What is that? What does that watershed planning really mean? And how do you think about your upstream and downstream neighbors? That's really really the critical scale of planning, so um we begin at the mouth of those watersheds at the mouth of the tidal creeks, this one church, creek outleting into the ashley and thinking about environmental change in a dynamic landscape.

G

How is this landscape projected to change itself as sea level rises? How is the marsh projected to migrate?

G

So we've done some preliminary mapping about where that marsh migration may be anticipated. This is important because this marsh this type of marsh habitat is a storm water sink. It also functions as somewhat of a storm surge buffer.

G

So it's important to understand where this landscape might be headed as waters rise and how to protect it, how to disincentivize things like barriers and a bulkheads that might ultimately result in the marsh extinction.

G

But here you see at a three level, three foot sea level rise projection in green, where marsh is expected to migrate and in red, where it's expected to be lost to be essentially drowned out when the water becomes too deep from the marsh to sustain itself.

G

This this map takes into account a slow sea level rise that allows the marsh to adapt over time and at a certain rate threshold. If things accelerate too quickly, the marsh won't be able to adapt so won't fulfill. These green shapes they'll become more of just open water or different types of water.

G

So there's a there's a range of time of time that we need to account for, but then we've also looked at um within those areas where the marsh is expected to migrate. What type of land use is existing there already and uh fortunately a lot of it is evergreen forest for this woody wetlands condition the two greens I know it's hard to read, but you see these kind of generally green impact areas, um which is good, so there's existing space for marsh to migrate and we can get some camp about protecting some of those areas.

G

um So there's the existing marsh itself as sea level rises. If it rises within a rate threshold where the marsh can accrete and adapt, we would expect to see the landscape changing some of these existing trees and more woody vegetation, converting dying back because of saltwater infiltration and converting into open marsh and, at the same time, higher water levels at the perimeter can push up groundwater levels inside the city, so we might expect to see some groundwater surfacing.

G

Essentially, these these white lines here are indicating a change between salt and fresh groundwater and the salt water tends to float it's less dense and actually tends to float on top of the the fresh water floats on top of the salty groundwater.

G

So this freshwater surfacing inland can be expected to be fresher generally than the salt water intrusion coming from the perimeter that might impact things like detention, ponds or inland drainage might, we might have ultimately submerged drainage systems rather than dry pipes, and we can. That might also indicate where selective relocations and adaptations might need to happen on a property by property basis.

G

We think about retreat or buyouts, not exactly part of the conversation right now, but think about those as wholesale changes along edges, when in fact they can be very targeted, especially for these localized impacts. This is what we're trying to avoid the sea walls and bulkheads that essentially, in all cases, result in marsh extinction. Marsh can't build up fast enough against that hard edge. You tend to get scouring depending on the rate of sea level rise.

G

You may ultimately get failure of these types of features, ending up putting the property that seems to be safeguarded behind the wall at some point in the future, at more risk.

G

We've done some work to characterize these landscape typologies across the city, both in terms of the planting and then the building typologies that might be adaptable within them so from the coastal edge. Again, you remember. This is referencing that prototypical section across the city lowlands uplands, but then also thinking about how to retrofit this urban and suburban landscape to be itself more adaptable, protect against things like heat heat, stress, adding shade, adding infiltration, protecting soils.

G

So we've looked at corresponding building typologies, residential and commercial flood adaptive versus non-adaptive. Again, this is just an early draft. We had some great questions about this on wednesday for thinking about it, integrating parking, maybe under buildings and a few other different types. So I think that's a lot of things we can add to this catalog and that was a great conversation but fundamentally slab on grade non-adaptive, other types of foundations pure and beam adaptive. They can change and elevate over time.

G

So this is both thinking about stipulating different types of construction that are fundamentally adaptive, but also what types of retrofits might be made commercial is a little tougher, especially the fill question uh try to avoid fill because that takes up volume in the flood plain, but in some limited cases, if you can offset around commercial structures with other types of strategies to mitigate runoff and add storage, that might be an acceptable adaptation.

G

So now, thinking about within that watershed scale, what are, what is the existing land use? What are your upstream and downstream neighbors doing, and how does that impact any particular property, so in red here in the shades of red? You see urban development from the dark red, densest urban development to the pink, which is more suburban, then out to the green, which is which is woods, forest and yellows being pastureland and agriculture and blues being some of the marsh and woody wetlands.

G

I think this kind of this is a national data set relatively coarse, but I think rings true to the experience on the ground we've taken that data set and applied it. Similarly, to the way we were looking at flood plain risk per foot of elevation zone, we've applied that land use data to each foot per portion of the city. So here's a draft from john's island.

G

You can see the specific shape of the in the amount of of land different elevations across the island, the amount of land within the flood plain across the island and then how the land use breaks down at different elevations.

G

I think what jumps out right away is you see this big gray shape this hatched gray shape, which is land outside the urban growth boundary so um well? There is a significant amount of land above 10 feet on john's island.

G

So excuse me one second, the door just blew open.

G

Got some rain storm blowing in right now new orleans? But if you look at this gray hatch here, even though there's a lot of land on john's island above 10 feet, a lot of it is outside the urban growth boundary.

G

Another thing that jumps out is the relatively small amount of red, so small amount of urban and suburban development relatively higher amounts of forest remaining on john's island within the urban ghost boundary. Even I'm going to flip ahead here to inner west ashley and just for a point of comparison.

G

These these merit a lot more close study and we've got them across the rest of the city, but I'll just flip back and forth. Here. What you see on interwest ashley is a lot more development, of course, a lot less forested area. You also see generally lower elevations of development, so that keep an eye on that 10 foot line back on john's island, not a lot of development. Still some forest, a lot of outside urban growth, west ashley much more developed.

G

You also see the floodplain characterization changes across the two so back to john's a little bit lower overall uh percentage of floodplain land in the flood plain.

G

And then on west ashley, you see those floodplain impacts creep up to slightly higher elevations.

G

A lot of that has to do. We think, with the generally low-lying long floodplains, which allow impacts to stack up so imagine rain, trying to run off trying to move across a much longer flat landscape, there's more opportunity for flooding along the way, but you can- and you can also imagine as we project this into the future- these impacts into the future with higher outfall, uh tidal elevations.

G

You can see this bulge of development that might start to be at risk as those percentages creep up to higher elevations.

G

We've tried to characterize the floodplains in different ways to understand these upstream and downstream relationships, and really there are two types, large and small, with the with the distinction in the large, the small tend to be mostly tidal kind of at the periphery draining directly into the ashley cooper or the harbor.

G

The large watersheds tend to capture more of this upstream inland condition, places like church, creek or james island, creek or knoll creek, maybe around daniel island, and these are key places to measure the upstream and downstream impacts. Because, obviously, what happens? The upstream neighbor is coming right to you.

G

The two different types within the large scale, watersheds are primarily tidal and then upland tidal is something like james island creek, where, even though it's a it's a large watershed um with a significant length of channel, it's mostly tidal, it's all very low lying, whereas something like church creek has a similar length of drainage channel, but those that kind of hinterland condition is no longer tidally impacted, and these, these different types might suggest different recommendations.

G

When you apply those to a map you can see in the darker blue here. What are what we consider the larger watersheds these these again are defined by the length of the outflow channel, so they're not actually defined by area, even though that generally correlates, but the length of channel is really important because that's where you get those compound impacts, stacking up the longer amount of time it takes for runoff to move through a watershed is really the critical factor, and within these larger watersheds there are upstream and downstream conditions.

G

So the darker blue, across the city, are the most upstream conditions, working all the way down to the lighter blue, which are more directly connected to the tail water to the the rivers and then in the harbor.

G

So those darker blue areas are the places to be most diligent in our view about um land, careful land use stewardship, because that's where the compound impacts will really begin for everything downstream, so some place like cane hoy, you already have a lot of forest cover. Some of some of this is within francis mary national forest.

G

That's a huge benefit to the communities and people and land use types farther downstream, really infiltrating and absorbing water similar upstream. In in church creek, where you could cause cascading consequences, all the way down to the outlet.

G

Getting close to finished here, a couple more slides within the watersheds also, I hinted at the beginning about the upland condition being more conducive to infiltration. So this is a map of the surface. Soil types and the thing to focus on here are the greens, the light green group b and the darker green group a are most suitable or most advantageous for stormwater infiltration.

G

So we can. We can we get a double benefit really from reserving those highest upland conditions, being careful stewards of that land and taking advantage of this infiltration capacity of the natural infiltration capacity of the landscape for for watershed benefits throughout.

G

So you see a upper church creek here you see some of the upland on the cainhoy peninsula, the high ground here into a little bit of an explanation about what exactly that means and the impact that we can see. um So, for example, if you remember those darker green soils, most advantageous for infiltration, highest sandiest soils, essentially where those former dune structures barrier sands are closest to the surface.

G

If you get a six inch rainfall, you could expect only two inches of runoff, so those soils in their natural state could absorb two-thirds of that rainfall.

G

Other thing to focus on here is this gray line. That's essentially a fully paved environment where, if you had six inches of rainfall, you would expect six inches of runoff, so the the impact is potentially dramatic for those group, a and group b soils and should be really carefully carefully preserved in their native state as much as possible.

G

Finally, last image here: um we've done a lot of other analysis again, this is just an overview, um but the last thing we presented here was the political boundaries and the overlapping political jurisdictions within each watershed.

G

So here you see in dark green, where the city has full jurisdiction over those watersheds and as you move up to orange and red, you see where there are multiple conflicting, potentially conflicting jurisdictions.

G

That's not to say there are more drainage problems in these watersheds. It's just to say that more coordination will be needed between more different types of entities in order to resolve drainage issues in these watersheds.

G

So it's um maybe just kind of a flashing light for more attention, rather not necessarily more problem, but I think this also rings pretty true, of course, on james island, um lots of small, one-off property impacts, different jurisdictions.

G

So, just to recap: these are the strategies that the city will be looking at going forward. This is jacob's slide and this will ultimately be up to the city to determine how to implement these different types of strategies.

G

So I will leave it there and turn it back, chloe and christopher and I'm happy to answer any any more questions.

D

Hey, thank you. Andy commission members, I'm sure there'll be comments or.

D

E

Miss jacobs has her hand raised.

D

Ms jacobs, you go ahead.

C

Hey andy, thank you again for that presentation. That's the third time! I've seen it and every time I see it, I've learned something: it's dense, you're right, but it's a it's a pretty thorough analysis. The um I had a question during one slide that I think maybe another slide is answering um the slide. I think it has land cover as a title and it's a two-sided, two graphs sitting next to each other one showing that um that one.

C

My question was in this original slide was how how all of these areas of the city are being used is that is that the way that slide is is being addressed like in each one of those floodplain, where you say: there's 60 miles um being used in this elevation of tidal influence. This is the density of development within that. Am I understanding that slide correctly.

C

I know that I I'm having a hard time even formulating the question, to be honest with you, but I think that's what this slide is telling us that the usage within each percentage of um the city under different water influences.

G

It's it's! It's two parts really, um this this portion on the right is identifying the the acreage within each foot of elevation and how it's being used.

C

G

So so, for example, at this 10th in inner west ashley at the 10 foot uh between 10 and 11 feet that foot you've got somewhere in the neighborhood of 80 acres uh cute, I'm sorry! This is, let's see something wrong with that. That's way too small, but um I think this might need to be percentage.

G

um But you see at that 10-foot threshold. It's it's essentially fully developed. So all.

C

Okay, that's what that's that's. My question was um the where where's the ability to grow um and it's it almost sounds somewhat conflicting, because we said we want to move our development into higher ground. Obviously, but at the same time you identify that some of the higher grounds are these evergreen forests that are actually sinking water. So we have to make sure we understand that too. I think that's what I heard from you also that I hadn't heard previously um is that correct too.

G

Right right, it's a it's, a real trade-off, and so there's a there's got to be a careful balance between where you grow, where it's safe to grow high up and where you need to manage the that impact flowing all the way down the rest of the watershed. Beginning. Okay, I.

C

Just wanted to make sure I was understanding that graph, because it is, it is difficult, but I think it's telling us a lot in there. Thank you.

D

Thank you. Thank you, mr jacobs. Thank you andy. Any other questions. uh Comments from commission members.

E

This olympus has their hand raised.

D

A

Am thank you, charlie um hi andy. Thank you for that presentation. um I wish I could see it on a larger screen um if you go back to the um slide, that has the houses and the elevations on it. um If you don't mind this one's, yes, that's it. um I had a question by some local builders and and christopher.

A

Maybe you can um assist with this that that they are being penalized, if that, let's just say, they're in a development, one development, it's in the flood area, part of it and the other part isn't, and they are getting penalized by building an elevated home if it's not necessarily in a e zone or a flood zone, um and I, after reading the dutch dialogues, I would think that that was encouraged actually in the dutch dialogues to elevate it um christopher. Is this something that that's going to change in the flood adaptive residential one?

A

How high is that pair and being grade that we're? Looking at as being available? It's really actually two questions.

F

So uh andy, how high is the purine beam and the flooded would be at the flood zone.

A

Yeah I mean uh-huh quite an adaptive, one.

G

It really, it really depends uh out on folly. Beach, of course, are the edges. Sometimes the bfe is is, is 12 feet or 14 feet that, as you move farther inland, it might just be a matter of of building with the future in mind, so maybe you're only maybe you're only building up uh two feet and it's just giving you the ability to incrementally raise if you need to over time, rather than being stuck in a slab on the ground and of course, some.

F

Base problems requiring you know two feet above that base flood elevation too. You know that's.

A

Right right, I knew that, but I mean, but um with with I guess, if somebody would like to elevate it, um would that actually count as a floor on the height bombs restrictions.

F

So in the downtown, if you have a six foot area or grader under the structure that counts as a floor in the height, but I think in our suburban areas it you it would not be in that kind of situation and you get a little bit of credit for the higher base. Flood elevation you've got to go to out there.

A

Well, I don't think that's actually happening. I think I mean I mean and again I don't know specifically, but I've heard that that's really not happening that they're having to build, and I would just think that and looking at all of these slides that that, if somebody, if a builder or you know, is, is willing to elevate, even though maybe the grade doesn't suggest, it should um andy. Would that be something that you would encourage or not encourage.

G

It's it's hard to say as a blanket statement, but I I would. I would say that what we're finding is it's important to take a little bit of a longer view than what we see as current conditions.

G

So, if you, if you look towards the end of a mortgage cycle, you might might see the landscape changing in ways that aren't necessarily anticipated at the beginning of the design, and so our our point really is just to create a as an as adaptive uh an environment as possible and not make decisions that um that might be regretted later or that might be saddle homeowners later unintentionally.

A

Well, have you all looked at how that affects the height? You know when we are looking at doing homes, we have to look at what the height is. So how we, you know you haven't, said much about how that how that changes, the height restrictions now.

G

And, to be honest, we haven't set those. um We haven't, found those target levels yet right.

F

Still early in this process, so that would come later and it may not even come completely in the comprehensive plan. I mean that might come in. You know updating zoning regulations after the plan has recommended. You know different types of development in different areas of elevation.

A

Okay, all right, thank you.

G

Maybe just one one more point to to build on that. You kind of see the range these these these levels are falling into, though there's something there's something kind of happening here where 100 percent starts to fall.

G

So that's at about an eight to nine foot, land surface elevation- and this is average across the city which we need to get more specific, um so the the eight to nine foot, land contour and the 12-foot land, contour or so end up being just things numbers to keep in mind so um homes built on land in those more rough ranges might need to consider different types of foundations.

G

Okay, that doesn't indicate the water depth of those locations. That's more of a case by case watershed by watershed.

A

Well, it's interesting because in the new flood maps that are actually due to be out on january, the 29th um in several areas that I know for a fact that flood they're actually coming down two feet. So I know I think part of the flooding areas that that happens in is probably more.

A

It's not really necessarily I mean it is tidal, but it's more storm drain runoff, that's not working well, um but I just think it's interesting that that we're trying to go higher here and and yet some of the flood zones are going from ae 11 to 89.

G

And this this data we're using, is actually the new fema floodplain.

A

It is okay, not interesting all right. Okay! Thank you. Andy you're welcome, mr.

D

Bailey, this is hand raised, go ahead, other questions or comments.

D

E

D

Go ahead, mr bailey go ahead. I.

H

I just maybe we could go down a big rabbit hole by asking questions like this, but what does the data assume um with respect to the the functionality of existing drainage infrastructure? Does it assume that it all works as designed.

G

It's a good question. um We looking really at surface flow for this. This purpose for this elevation uh this analysis, so um we haven't modeled, for example the the all of the pipes. um These are. These are conveyance channels, and things like that. um You know in a word. Yes, I think it's somewhat of an idealized state. It assumes a degree of routine maintenance.

G

What you do see, though, is on, for example, on daniel island. That drainage system is relatively low lying.

G

However, perhaps better maintained and and functional it's daniel island's, not really any higher than west ashley in terms of land elevation, but it's a bit more of a functional system, so really we're not getting too far into the weeds um particular blockages in different pipes here and there we're really looking at the the bigger tidal creeks, the the bigger creeks and channels, it's just. It gets a little bit overwhelming across the scope of the whole city to focus in too much so we kind of had to to a certain point at the watershed scale.

G

I don't know if that answered your question.

H

Yeah, I I mean my professional life. I manage about 60 miles of underground drainage, so um just because it's there doesn't mean it functions, so I think about it. A lot.

G

There there are relative moments that I'm aware of where watersheds are bridged by um on other types of underground conveyance.

G

I think they tend to flow towards uh um a main creaker channel within a watershed, and so that way we've we can sort of isolate those impacts. um It's not a we're. If we're looking watershed by watershed, those impacts from a clogged drain aren't going to necessarily spill it over into the next.

D

Thank you. Thank you, mr bailey. I think it was a good question. Other questions comments from commission members.

C

I have another question.

D

Please go ahead. Miss jacob should go ahead.

C

The the graph that's similar to this one but has um lindsay's little graphs on top of it like in this, that one where you reserve, defend, adapt and grow, and this area that you're recommending reserve, if it's already densely developed in some areas or is there going to be a retreat strategy for those areas? Because we can't reserve something. That's already densely developed.

G

A critical question for the city going forward: we're not making uh we're not making recommendations about where to implement certain strategies, we're just um presenting the the range of scenarios really, and um I think I think that's a policy uh question and conversation going forward. Thank.

C

D

Thank you, vs jacobs. I think we have a lot of challenges both with the existing areas like intel projects, as well as new subdivisions, new areas being developed. So um thank you andy and thank you. Commission members, um christopher. What's next.

E

Mr lisane has his hand raised charlie, and I also wanted to add something in response to mr bailey's question.

E

um So something that I did want to mention that is uh that is going on, and I is the stormwater department is doing- is acom, which is another consultant group has been working for quite some time now on. um They are looking at the infrastructure and drainage systems of the city, so that it's not that the city is not looking at that layer of things.

E

It's just not happening within the scope, necessarily of of what the uh water team is looking at for the city plan, and I don't know if andy wants to add a little bit more on onto the discussions that they've had with stormwater staff, but that that analysis is ongoing and we'll have more data from that. Hopefully soon.

D

Andy, do you want to add anything on that or.

G

I know I think I think chloe got it.

C

I can, I can actually add a little bit because matt fountain gave a presentation to peter shaheed's constituent zoom this past saturday on that very subject where they are, in that whole analysis of the drainage system. How what they've got cleaned? What they're getting on a schedule and stuff like that. He did a pretty nice presentation for the constituents in that district because they have some questions.

D

Okay, thank you, mr jacobs. uh Mr losing you had a question. I think correct.

I

Yeah, I did thank you, charlie and I'm gonna. um I'm gonna stop my video. While I ask my question: I'm competing with lots of people for my internet service here tonight. I just want to say a number of these questions sort of get to the issue about policy, and I just I wanted to say thank you to to andy, uh but also to the city staff and to the city.

I

More generally, I mean what what we're seeing here is the compilation of a lot of data that we never had access to before, and this is critical data that we're all going to be having to use from here going forward to make a lot of complicated and difficult decisions.

I

And so you know, I don't think anybody's got the answers today. What all this means, uh but we know it means some pretty profound things and that we're going to have to study this and become really smart about something that we've never really had acts uh you know had to do before, but now at least we have this data.

I

Due to uh to to everybody who's involved in the collection, and- and you know this preliminary analysis of this data- um we've all got a lot of work to do not just this commission but this community when it comes to figuring out what we do about this I mean we've just touched on some of the big issues now, but um this is a very uh daunting challenge.

I

I'm I'm really kind of humbled by this data, uh because there is uh you know ms jacobs last question about you know: where does this mean we need to retreat? Well, I mean, I think the water is going to take it back, whether we retreat or not at some point, so we really need to start.

I

You know we just need to start preparing people, and I know that's what this discussion is part of this is about is letting people know that there are some really difficult challenges ahead of us as we try to plan and adapt this city for what's coming and and the water's coming, we know it so anyway, that's all.

C

I

Would like to, I would like to echo.

C

What harry is pointing to because um there was a very important slide that andy showed us? It's called. um I think it was called water and politics that showed all the multi-jurisdictional um influences on our watershed, and some of them are really even outside of our city boundaries. um Where there's you know major decisions being made by other um other municipalities.

C

Other counties- and one perfect example we have right now is the building the proposed building of, I think was- was 950 homes that are going to be coming up on that land that was annexed into north charleston up highway, 61 that that we will have absolutely no say-so in but will highly impact all the developments around us our watershed around us. I don't know that it directly impacts church creek, but it's close to those watersheds up there.

C

So we have a dual challenge: an internal challenge for our city moving forward and then negotiating in the region that we're all good neighbors with each other about where the water is that's going to be another challenge.

D

Thank you well said mr lesane and miss jacobson. I guess we talk about retreat. We know the city's had to buy back homes and things like that in areas that were flood flowing, I think shadow, moss and church creek whatever that area, so we certainly want to in future plans try to plan if we can to avoid those kind of things. Mr morgan, what's next.

F

Well, you know, I think you all have definitely um captured the fact that this is very significant information.

F

um I think this is you know this information is going to lead to a plan that will be, unlike any other plan, we've had before, but it's a plan that is needed in the times that we're in and with the threats that we face.

F

So um I really appreciate y'all's attention to this, because this is really at the heart of you know what this document will be um and and some of the key recommendations and policy recommendations that we will have to be discussing in coming months.

F

So um I really appreciate y'all's attention to this and questions and um andy and your crew. I mean just amazing information and again we're going into this planning process with data that we've never had before and it's fantastic to have it, but it's also very humbling.

D

Mr morgan, anything else on the agenda today.

F

I think that's it unless any other commissioners have questions or comments.

D

Well again, I want to echo mr uh the same thoughts thanks to the staff for putting this together.

D

uh Thank you for commission members for your time, but thanks for staff putting this together because it's a lot of work, it's a lot of information and very important information for us to plan for a positive future other questions or comments from commission members yeah. If not, I guess we'll be adjourned.

D

Thank you. All.

F

B

Thank you. Thank you.

I

Thanks thanks, everybody.

I