20200715-003b: Persimmons SP-2018-0579C.SH variance packet — original pdf

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ITEM FOR ENVIRONMENTAL COMMISSION AGENDA COMMISSION MEETING DATE: July 15, 2020 NAME & NUMBER OF PROJECT: NAME OF APPLICANT OR ORGANIZATION: LOCATION: Persimmons (SP-2018-0579C.SH) Mike Mullone, Dunaway & Associates 7051 Meadow Lake Boulevard, Austin, TX 78744 COUNCIL DISTRICT: District #2 ENVIRONMENTAL REVIEW STAFF: Jonathan Garner, Environmental Program Coordinator, Development Services Department, (512) 974-1665, Jonathan.Garner@austintexas.gov WATERSHED: REQUEST: Onion Creek Watershed, Suburban Watershed Classification, Desired Development Zone Variance request is as follows: Request to vary from LDC 25-8-341 to allow cut of more than four feet on slopes in excess of 15 percent gradient. STAFF RECOMMENDATION: Staff recommends this variance, having determined the findings of fact to have been met. STAFF CONDITION: Revegetate the top and backside of the detention pond berm with native, deep-rooted bunch grasses, and provide additional tree protection for trees 4-8” in diameter located along the steeper slopes. Staff Findings of Fact Variance to LDC 25-8-341 Development Services Department Staff Recommendations Concerning Required Findings Project Name: Ordinance Standard: Watershed Protection Ordinance Variance Request: Persimmons (SP-2018-0579C.SH) Request to vary from LDC 25-8-341 to allow cut of more than four feet on slopes in excess of 15 percent gradient. Include an explanation with each applicable finding of fact. A. Land Use Commission variance determinations from Chapter 25-8-41 of the City Code: 1. The requirement will deprive the applicant of a privilege available to owners of similarly situated property with approximately contemporaneous development subject to similar code requirements. Yes. The project proposes a multi-family, affordable housing project in an area conducive to such a development. All along the East William Cannon Dr. corridor, there are a number of multi-family developments that are constructed on slopes within the 0-15 percent category. All of the proposed impervious cover with this project is similarly situated on the portion of the property within the 0-15 percent slope category. The proposed water quality and detention pond are required by the Land Development Code, and the project intends to incorporate an amphitheater amenity into the design of the detention pond in order to foster community engagement by hosting events for the multi-family development. 2. The variance: a) Is not necessitated by the scale, layout, construction method, or other design decision made by the applicant, unless the design decision provides greater overall environmental protection than is achievable without the variance; Yes. The variance request is necessitated by the layout of the site plan, but to the degree that the proposed layout provides greater overall environmental protection by achieving the following: • All of the proposed cut is located outside the 500-year floodplain; • No Protected Class trees (>19” diameter) will be removed for the construction of the ponds; • The slopes that will receive the cut descend towards a large area of flat open land (0-15% slopes) that is shared PARD property and a gas line easement, and no other development will be proposed at the bottom of the slope that would be adversely impacted by the proposed construction; • The location and footprint of the pond avoids any conflict with the existing wastewater lines at the southern end of the property; • The pond design will make a vertical cut in the slopes and reinforce the cut side with a concrete trapezoidal wall with stone veneer (see Pond Section in exhibit labeled Detention Pond Plan, page 20); and, • The pond takes advantage of the natural slope of the land, and by locating the pond in this proposed location, the project does not seek to significantly alter the existing drainage patterns. b) Is the minimum deviation from the code requirement necessary to allow a reasonable use of the property; Yes. The project does not seek to maximize development on the property with regards to allowable impervious cover (33% Gross Site Area proposed, 65% Gross Site Area maximum allowable), therefore the cut needed for the pond to capture the required water quality and detention volume is only necessitated by the amount of impervious cover proposed on the site. If the project were to maximize the amount of allowable impervious cover on the site, the water quality and detention facility would have to be enlarged in order to capture the required volume, which would most likely require expanding the footprint of the pond and locating the cut over four feet on slopes of a steeper category (25-35% gradient). c) Does not create a significant probability of harmful environmental consequences. Yes. A different layout of the pond that would not require cut of more than four feet would also require locating the 0-4’ cut onto the steeper slopes (25-35% gradient), require the removal of Protected Class trees, require the outfall of the pond to be located on the steeper slopes of the site – possibly generating a need for a cut variance for the outfall structure –and, has the probability of requiring cut within the 100-year floodplain. 3. Development with the variance will result in water quality that is at least equal to the water quality achievable without the variance. Yes. All cuts will be stable, vertical cuts that will be reinforced with concrete retaining walls to prevent erosion from occurring in the location of the cut. The disturbed areas within the vicinity of the cut will be required to be restored with native, deep-rooted bunch grasses and other forbs indicative of a Blackland Prairie. B. The Land Use Commission may grant a variance from a requirement of Section 25-8-422 (Water Supply Suburban Water Quality Transition Zone), Section 25-8-452 (Water Supply Rural Water Quality Transition Zone), Section 25-8-482 (Barton Springs Zone Water Quality Transition Zone), Section 25-8-368 (Restrictions on Development Impacting Lake Austin, Lady Bird Lake, and Lake Walter E. Long), or Article 7, Division 1 ( Critical Water Quality Zone Restrictions ), after determining that:: The criteria for granting a variance in Subsection (A) are met; N/A 1. 2. 3. The requirement for which a variance is requested prevents a reasonable, economic use of the entire property; N/A The variance is the minimum deviation from the code requirement necessary to allow a reasonable, economic use of the entire property. N/A Staff Determination: Staff determines that the findings of fact have been met. Staff recommends the following condition: • Revegetate the top and backside of the detention pond berm with native, deep-rooted • Provide additional tree protection for trees 4-8” in diameter located east of the proposed bunch grasses; and, pond along the steeper slopes. Environmental Reviewer (DSD) __________________________ Jonathan Garner Environmental Review Manager (DSD) Environmental Officer (WPD) Mike McDougal Mike McDougal _____________________________ Chris Herrington Date 6-11-2020 Date 6-11-2020 Date ______________ 06-24-2020Application Form Variance to LDC 25-8-341 January 21, 2020  ENVIRONMENTAL COMMISSION VARIANCE APPLICATION FORM   Mike Mullone 5707 Southwest Parkway, Suite 250 Austin, Texas 78745 512-399-5373 mmullone@dunawayassociates.com Persimmon SP-2018-0579C.SH 7051 Meadow Lake Boulevard PROJECT DESCRIPTION Applicant Contact Information Variance Case Information Name of Applicant Street Address City State ZIP Code Work Phone E-Mail Address Case Name Case Number Address or Location Environmental Reviewer Name Environmental Resource Management Reviewer Name Applicable Ordinance Watershed Name Watershed Classification Jonathan Garner N/A LDC 25-8-341(A)(4) Onion Creek ☐Urban ☐Water Supply Rural ☐ Suburban    ☐Water Supply Suburban ☐ Barton Springs Zone City of Austin | Environmental Commission Variance Application Guide  1  January 21, 2020  Edwards Aquifer Recharge Zone Edwards Aquifer Contributing Zone Distance to Nearest Classified Waterway Water and Waste Water service to be provided by City of Austin ☐ Barton Springs Segment ☐ Not in Edwards Aquifer Zones ☐ Northern Edwards Segment ☐ Yes ☐ No 0.5 miles to Onion Creek (Suburban Watershed)  The variance request is as follows (Cite code references): Per LDC 25- 8-341(A)(4), grading over four feet for construction of a water quality control or detention facility is not allowed on an existing slope with a gradient of more than 15 percent. Existing  ________  0.00  0% Proposed  _________  4.32  33.1%  Habitat for Humanity proposes to construct 126 affordable housing units which  qualify as SMART Housing.  There are no current improvements on the site.  The  site improvements will include 18 buildings (for 126 residential units), water and  wastewater utilities, storm drain utilities, open space community play area,  water quality and detention ponds.  The improvements will require grading with  cutting more than 8 feet on slopes over 15% for a detention pond.    Slopes range from 1% to 25%.  Highest elevation 587, Lowest elevation : 540  Mature trees and grass are the main site vegetation. There is a CWQZ for the  unnamed tributary to Onion Creek that runs along the southern end of the  property.  There is a floodplain for each the Onion Creek and the unnamed  tributary to Onion Creek.   No improvements will be located in the CWQZ or the  floodplains.  There are no CEFs or Heritage Trees on this Site.  Request Impervious cover  square footage:  acreage:   percentage:  Provide general  description of the  property (slope  range, elevation  range, summary of  vegetation / trees,  summary of the  geology, CWQZ,  WQTZ, CEFs,  floodplain, heritage  trees, any other  notable or  outstanding  characteristics of the  property)  City of Austin | Environmental Commission Variance Application Guide  2  January 21, 2020  Clearly indicate in what  way the proposed project  does not comply with  current Code (include  maps and exhibits)  FINDINGS OF FACT  Project:  Ordinance:   Per LDC 25‐8‐341(A)(4), grading over four feet for construction of a  water quality control or detention facility is not allowed on an existing  slope with a gradient of more than 15 percent.  A detention pond and dual use amphitheater is proposed in an area  where the slope is over 15%. As required in LDC Section 25‐8‐41, in order to grant a variance the Land Use Commission must make  the following findings of fact:    Include an explanation with each applicable finding of fact.  A. Land Use Commission variance determinations from Chapter 25‐8‐41 of the City Code: 1. The requirement will deprive the applicant of a privilege available to owners of similarly situated property with approximately contemporaneous development subject to similar code requirements. Yes / No  [provide summary of justification for determination]  Due to the unique topography of this Site, it all drains to the adjacent creek.   Maximizing of affordable units is clustered on the 0% ‐ 15% slope land. The  layout requires the detention pond be located in the area where the slope starts  to increase toward the creek  2. The variance: a) Is not necessitated by the scale, layout, construction method, or other design decision made by the applicant, unless the design decision provides greater overall environmental protection than is achievable without the variance; [provide summary of justification for determination] Yes / No  The pond location was chosen to minimize tree removal and to be adjacent to residences so alternate use as amphitheater was assessible to home owners City of Austin | Environmental Commission Variance Application Guide  3  January 21, 2020  b) Is the minimum deviation from the code requirement necessary to allow a reasonable use of the property; [provide summary justification for determination] Yes / No  ‐The layout maximizes green space within the development which provides increased environmental protection. ‐There is minimum amount of slope impacted by the pond design. ‐The construction will stabilize the slope and will not create harmful environmental consequences. ‐The detention pond and associated water quality pond will meet current standards. c) Does not create a significant probability of harmful environmental consequences. [provide summary justification for determination] Yes / No  The construction on slopes consists of a detention pond that will be fully revegetated with grass and new trees around the pond. 3. Development with the variance will result in water quality that is at least equal to the water quality achievable without the variance. Yes / No  [provide summary justification for determination]  The construction on slopes consist of detention pond which will be fully  revegetated with grass and new trees around the pond.  No impervious cover is  proposed on these slopes, and no slope erosion is anticipated.   B. Additional Land Use Commission variance determinations for a requirement of Section 25‐8‐422 (Water  Quality  Transition  Zone),  Section  25‐8‐452  (Water  Quality  Transition  Zone),  Article  7, Division  1  (Critical  Water  Quality  Zone  Restrictions),  or  Section  25‐8‐368  (Restrictions  on Development Impacting Lake Austin, Lady Bird Lake, and Lake Walter E. Long): 1. 2. 3. The criteria for granting a variance in Subsection (A) are met; [provide summary of justification for determination]  Yes / No  The requirement for which a variance is requested prevents a reasonable, economic use of the entire property; [provide summary of justification for determination] Yes / No  The variance is the minimum deviation from the code requirement necessary to allow a reasonable, economic use of the entire property. Yes / No  [provide summary of justification for determination]  **Variance approval requires all above affirmative findings.  City of Austin | Environmental Commission Variance Application Guide  4  Jonathan Garner City of Austin Development Services Department 505 Barton Springs Road, 4th Floor Austin, Texas 78704 January 21, 2020 Re: Persimmon (SP-2018-0579C.SH) 7051 Meadow Lake Boulevard, Austin, Texas 78744 Land Use Commission Variance for Administrative Cut/Fill Variance Request (LDC 25-8-341(A)(4)) Dunaway UDG # 17-949 Mr. Garner, Habitat for Humanity proposes to construct 126 affordable housing units which qualify as SMART. There are no current improvements on the site. The site improvements will include 18 buildings (for 126 residential units), water and wastewater utilities, storm drain utilities, open space community play area, water quality and detention ponds. The improvements will require grading with cutting more than 8 feet on slopes over 15% for a detention pond. Per LDC 25-8-341(A)(4), grading over four feet for construction of a water quality control or detention facility is not allowed on an existing slope with a gradient of more than 15 percent. We are requesting support and approval from the Environmental Reviewer on this project to get variance approval from the Land Use Commission. The reasons we are requesting approval as it pertains to the Findings of Facts is as follows: 1.) Due to the unique topography of this Site, it all drains to the adjacent creek. Maximizing of affordable units is clustered on the 0% - 15% slope land. The layout requires the detention pond be located in the area where the slope starts to increase toward the creek. 2.) a. The layout maximizes green space within the development which provides increased environmental protection. b. There is minimum amount of slope impacted by the pond design. c. The construction will stabilize the slope and will not create harmful environmental consequences. 3.) The detention pond and associated water quality pond will meet current standards. 4.) The pond location was chosen to minimize tree removal and to be adjacent to residences so alternate use as amphitheater was assessible to home owners 5.) The construction on slopes consist of detention pond which will be fully revegetated with grass and new trees around the pond. No impervious cover is proposed, and no slope erosion is anticipated. Applicant Exhibits Variance to LDC 25-8-341 Engineering Firm #F-1114 TX Registered TBPLS Firm No. 10065900 5707 Southwest Building 2, Suite 250 Parkway PERSIMMON AERIAL WITH BOUNDARY TX 78735 !Austin, 5: ------------------------------------------------------------_.... ------....... ----......1 Phone: 512-306-8252 SP-2018-0579C.SH 9 8 1 2 17 WH WH WH 18 WH 3 10 4 5 11 15 WH WH 16 13 6 14 12 7 HATCH LEGEND SYMBOL DESCRIPTION PRIVATE COMMON OPEN SPACE STREETYARD AREA UNDISTURBED NATURAL AREA Texas Firm #F-1114 TBPLS Firm No. 10065900 5707 Southwest Parkway Building 2, Suite 250 Austin, TX 78735 Phone: 512-306-8252 0 1 2 1 IF THIS BAR DOES NOT MEASURE 1" THEN DRAWING IS NOT TO SCALE THESE PLANS ARE UNDER REVIEW BY THE C.O.A. AND ARE NOT APPROVED FOR CONSTRUCTION. (THIS NOTE TO BE REMOVED ON FINAL, APPROVED PLANS.) N O M M S R E P I S A E R A E P A C S D N A L D E R U Q E R I SP-2018-0579C.SH SHEET NUMBER 38 OF 49 ' ' ' ' ' ' ' ' ' ,_ ' '' _-, ' ' , ' �� ' o;.> ' ', I , ' � :i' ,, ' ' . ' , , b ( .... ' -- -... , ' ' ' ' • ' ' ' ' ' ' • -- ' ' -' / - ' ' , , --- ' ' ' ' ' ' ' ' ' I, __ , , ' ,,_ 'µ'" ' ' _< '!,, ... ..... � '!,,1;1 ' ' ' '-, .i ' '-./;,/ -; , ' , I -"'- /� ,' \ � / .... ' , , r -• ., ', ... -\ \ ... ., ' " -" f ,. .. r. " ' , ' ' , ' ', ' ' -, , " ', - - ' ' , , ,, , ,_ • • ' ' ' ' ... ,. .. .,,,, ·< ' , , ' ' , , SLOPE CATEGORIES 0-15% 15-25% 25-35% , ' , - .\ ,, 35%+ z Q.... a. QC (.} VJ w 0 z 0 iii > I!! w !:c" >­ ID SCALE: I"= 60' � 0 � IF THIS BAR DOES NOT 1 MEASURE 1" THEN DRAWING IS NOT TO SCALE TIIESE PLANS ARE UNDER REVIEW BY TIIE C.O.A. AND ARE NOT APPROVED FOR CONSTRUCTION. (THIS NOTE TO BE REMOVED ON FINAL, APPROVED PLANS.) a. z ,c 0 ::!E ::!!!: ::!!: Ill en a. 0::: 0 w ..... a_ rn c O' '" � ' "' (!] (!] ' I "- I / "� • • l (!] / c 0 [L •� " c (!] 0 0:: / 0 -<: u l-��--1..�����-,0N '° �DU NAW AYllID en ' Texas Firm No. F-1114 TBPLS Firm No. 10065900 Parkway 5707 Southwest Building Austin, Phone: 512-306-8252 2, Suite 250 TX 78735 11812020 SL ' -,' �', .. . ,,,, , ,,-; / ""r--;� I /1\ .,...f_fI 0 ,, ' "' Basin ID Impervious CN weighted Total Q (H) Total Q (R1+R2) Total Q (Existing) - ToC min. 16 5 5 Existing Hydrologic Summary Q2 ft3/s 24.5 7.2 1.6 24.5 8.8 29.0 80.6 93.3 95.1 Proposed Hydrologic Summary ToC min. 5 14 5 5 Q2 ft3/s 30.6 9.8 7.2 1.6 - 88.9 80.0 93.3 95.1 % 3 74 84 % 50 0 74 84 Q10 ft3/s 62.2 13.1 2.8 62.2 16.0 71.1 Q10 ft3/s 61.4 25.2 13.1 2.8 Area ac. 14.33 1.75 0.37 Area ac. 8.70 5.63 1.75 0.37 Q25 ft3/s 81.6 15.9 3.4 81.6 19.4 92.6 Q25 ft3/s 76.1 33.2 15.9 3.4 Q100 ft3/s 113.4 20.4 4.4 113.4 24.7 128.2 Q100 ft3/s 98.6 46.1 20.4 4.4 - H R1 R2 - H1 H2 R1 R2 Basin ID Impervious CN weighted Detention Inflow 30.6 61.4 76.1 98.6 Detention Outflow 3.9 29.9 43.7 64.3 Detention WSEL (ft) 554.9 557.1 557.9 559.0 Detention Storage (ac-ft) 0.74 1.22 1.42 1.69 Total Proposed Q Leaving the Site 11.1 54.9 76.8 110.4 Q Summary Existing (H) Proposed w/ Det.(H1+H2) Q2 ft3/s 24.5 Q10 ft3/s 62.2 Q25 ft3/s Q100 ft3/s 81.6 113.4 11.1 54.9 76.8 110.4 Flow Reduction -13.4 -7.3 -4.8 -3.0 Detention Outlet Structure Outlet # Structure Size Elevation 1 2 Orifice Weir 5" 27" 550.4 554.4 Detention Pond Summary Stage-Storage-Discharge Storm Qpond in Qpond out WSEL Storage - 2YR 10YR 25YR 100YR ft3/s 30.6 61.4 76.1 98.6 ft3/s 3.9 29.9 43.7 64.3 ft. 554.9 557.1 557.9 559.0 ac-ft. 0.74 1.22 1.42 1.69 Elevation Volume Cum. Vol. Cum. Vol. Detention Pond Volume Summary Area ft2 0 ft3 0 ft3 0 ft. 550.40 552.00 554.00 554.50 556.50 557.00 559.00 559.50 561.50 8152 8631 9406 9874 10706 11164 12052 12499 Area ac. 0.000 0.187 0.198 0.216 0.227 0.246 0.256 0.277 0.287 6522 16783 4509 19280 5145 21870 5804 24551 6522 23305 27814 47094 52239 74109 79913 104464 ac‐ft. 0 0.150 0.535 0.639 1.081 1.199 1.701 1.835 2.398