Fort Walton Beach Council agenda — 06-03-08 workshop agenda — reading text

credits every four (4) years. Examples of efforts customers can make that generate less runoff or runoff at a slower rate, or contribute less polluted runoff include the following with the maximum credit amount shown at the end of each option: Pervious Pavers and /or Asphalt replacing existing impervious surfaces ( credit depending on void space provided): 5 % 1- 5% credit Rain -barrels to collect runoff from roofs for a secondary use such as irrigation with 25 -year storm or 1" of runoff volume: 50% credit Redirecting gutter downspouts to infiltration area: 30% credit Grade modifications to retain a percentage of runoff on -site: 30% credit Vegetated Natural Buffer ( 20 ft minimum width) along surface water bodies: 20% credit Impervious area accounts for less than 10% of total parcel area with no direct runoff: 30% credit CITY OF FORT WALTON BEACH STORMWATER UTILITY IMPLEMENTATION PLAN REPORT TETRA TECH May 28, 2008 19 4.2 Right of Refusal to Connect to Utility Stormwater Utilities are intended to be set up and operated similar to other City operated utilities. One aspect is the fact the City's other utility departments provide the right to a City resident to not connect to the utility. In establishing a stormwater utility, that same right is usually afforded to the residents through a program similar to the mitigation credits. With a Right of Refusal to Connect, an entity usually requires that efforts above and beyond the mitigation steps be implemented and certified by a professional engineer. In most cases, the requirements revolve around a demonstration that runoff from specific storm events is retained within a property. The following language is proposed for the City of Fort Walton Beach for a right of refusal to connect to utility element as part of the City's Stormwater Utility system: Any person or entity responsible for paying the stormwater user fee, who chooses not to use stormwater program services, may elect to develop their property in a manner that retains all stormwater discharges on -site and therefore will not be discharging to the City's stormwater infrastructure. if all stormwater is retained on -site, the property will not be subject to stormwater user fees. The responsible party must verify retention of all stonnwater on -site by submitting, for review and approval by the City, certified engineering drawings and calculations demonstrating that one hundred ( 100) percent of the total volume of runoff from the property will be retained within the property. The engineering calculations shall be based on runoff volumes from the one-hundred-year frequency rainfall event, for the following durations: one ( 1), two (2), four (4), eight (8) and twenty -four (24) hours and one ( 1), two ( 2), three ( 3), four (4), seven ( 7) and ten ( 10) days. Retention means to keep on site without ever discharging. CITY OF FORT WALTON BEACH TETRA TECH STORMWATER UTILITY IMPLEMENTATION PLAN REPORT 20 May 28, 2008 5. 0 EQUIVALENT RESIDENTIAL UNIT DETERMINATION 5. 1 INTRODUCTION To determine an Equivalent Residential Unit for the City of Fort Walton Beach an impervious area sampling was performed on single family residential properties. Using high quality aerial photography in a GIS platform, a sampling was performed throughout the City on single family residential properties to determine the amount of impervious areas. Surface areas were generated for both roof top and pavement areas for all sampled properties by digitizing an outline over the aerial photos and calculating a total impervious area within the outline. 5.2 DATA ANALYSIS The random sampling for impervious areas on the single family residential parcels was simply based on the property appraiser's building sizes. It is understood that there is not direct correlation between a parcel's building size and the total impervious area, however this is just a point from which to start the " random" sampling. The parcels were sorted by land use and all single family residential parcels were extracted to a separate file. The single family residential parcels were linked to the database file containing the building sizes. The count of single family residential properties with existing buildings is 6,236. A statistical analysis was performed on this single family residential parcel layer based on the building sizes which provided the following: Field Fre4t1enCy DWFIMER" stow= 1, 500 Count: G296 Minimum 52'I Maadwa 10484 1, 000 Sum: 13414036 Mean: 2151. 064144 500 9landand Dewahm ffig.657276 0 520 2512 4504 6495 8488 10480 1516 3308 5500 7492 9484 Based on this statistical analysis, the building sizes range from 520 to 10,484 square feet with a mean size of approximately 2,151 square feet. Based on the mean building size, approximately 10 percent of the SFR parcels were selected for impervious sampling by selecting 5% of parcels below the mean and 5% above the mean. A total of 629 properties were sampled in this manner with a range in impervious area from 63 square feet to over 12,960 square feet. CITY OF FORT WALTON BEACH STORMWATER UTILITY IMPLEMENTATION PLAN REPORT TETRA TECH 21 May 28, 2008  Figure 5- 1 shows the single family residential properties sampled in the City. The parcels sampled were determined based on a statistical distribution of properties to ensure a sampling of a variety of sizes was included. Figure 5-2 provides a closer look at the single family residential properties sampling. The mean area from this distribution of the impervious areas is 2,717 square feet. Based upon a thorough sampling throughout the City, an equivalent residential unit (ERU) equal to 2,700 square feet is recommended for the City of Fort Walton Beach. CITY OF FORT WALTON BEACH TETRA TECH STORMWATER UTILITY IMPLEMENTATION PLAN REPORT 22 May 28, 2008 LEGEND: FIGURE 5 -1 Sampled Single Family CITY OF FORT WALTON BEACH Residential Parcel STORMWATER UTILITY MASTER PLAN SINGLE FAMILY RESIDENTIAL SAMPLING LOCATIONS complex world; CLEAR SOLUTIONS" TETRA TECH  6.0 REVENUE PROJECTIONS 6. 1 INTRODUCTION The ERU for single family properties was coupled with data from the Okaloosa County Property Appraiser and analyzed to determine the count of the various types of properties within the City. 6.2 DATA ANALYSIS All Fort Walton Beach parcels were gathered from the Okaloosa County Property Appraiser in the form of a Geographic Information System ( GIS) point shapefile. The file included a point placed over each parcel. The number of parcels in this file totaled 8,893. Table 6 -1 provides a summary of the types of land use identified in the City and Figure 6 -1 shows the geographic distribution of the various types of current land uses in the City. TABLE 6-1 CITY OF FORT WALTON BEACH STORMWATER UTILITY IMPLEMENTATION PLAN SUMMARY OF CITY LAND USE DESIGNATIONS & DISTRIBUTION Parcel Land Use Designation Count Acres Commercial 552 371. 4 Office 142 49.3 Industrial 122 255. 7 Transient Lodging 16 24. 5 Low Density Residential 6418 1794. 7 Low Medium Density Residential 584 110.9 Medium Density Residential 280 55. 7 Public Land & Buildings 100 213. 7 Parking 22 6. 8 Recreational 73 468. 6 Religious 77 56.5 Educational 21 226. 8 Utilities 12 25. 2 Vacant 474 259. 9 TOTALS 8893 3919. 7 Summa Commercial 832 700. 9 Residential 7282 1961. 3 Public 305 997. 6 Vacant 474 259. 9 CITY OF FORT WALTON BEACH STORMWATER UTILITY IMPLEMENTATION PLAN REPORT TETRA TECH May 28, 2008 25  LEGEND EXISTING LAND USES Low Density Residential ( 6,418) Public Land & Buildings ( 104) Transient Lodging ( 15) Commercial ( 552) Parking ( 22) Utilities ( 12) Low Medium Density Residential ( 586) Recreational ( 73) Vacant (473) Of Educational (21) Medium Density Residential (280) Industrial ( 122)