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Home My WebLink About20061042 Ver 3_Stormwater Info_20111201 l WITHERS �' RAVENEL cesz ENGINEERS I PLANNERS I 5URVEYORS December i 2oii Ms Annette Lucas NCDENR Division of Water Quality 5iz N Salisbury Street Raleigh NC 27626 � D ��QL%� Re Ashton Hall Subdivision — Phases 3&4 D Durham NC �E� � 1 ?0" DWQ Pro�ect#06 io42 v 3 wE �ENR WqTER W&R Pro�ect#02090500 0 ��S'�►'OSTpR��R �NCH Dear Ms Lucas Please�nd attached three (3) copies of Diffuse Flow Plans and supporting documents for the above referenced pro�ect This information is provided in response to your November zz 2oii letter requesting additional information The additional information requested is listed below followed by a written response Additional lnformation Requested i Please p�owde one Leve/ Spreader Supplement form for each proposed level spreader available athttp//portal ncden�or.g/web/wq/ws/su/bm,v manual Please include the required items checklist and all items listed therein Response Included with this submitta!are three (3) copies each of the following documents • Diffuse Flow Plans (i3 sheets) • Stormwater Impact Analysis Memorandum (3 pages) • Flow Splitter Worksheets (3 pages) • Plunge Basin Dissipator Report(i page) • Level Spreader Vegetated Flter Strip Supptement (one supplement each for all three level spreaders-9 pages total) • Fitter Stnp Restored Riparian Buffer and Level Spreader Operation&MaintenanceAgreements (one each for all three level spreaders—9 pages total) If you need any additional informa�v�o�r�h��ny questions please give me a call at 919 469 3340 �'�� ' ��! ��I Sincerely � ��f M � � � WITHERS VENEL I C � � �� .� / � Bradle Hart PE �y�/�� f�i`��\�~ � �'rjr��°�'� 1�,,``� cc Patrick Atlen — Beazer Homes Corp fi le iii MacKenan Drroe�Cary NC 275ii �tel 919 469 3340� fax 9i9 238 zo99 I�withersravenel com ipio Commonwealth Dnve�Suite ioi�Wilmington NC i8yo3 I tel 9zo 256 9z77�fax 9zo 256 2584 4i6 D Gallimore Dairy Road I Greensboro NC 27po9 i tel 336 993 5504 1 c-e3z ENG�NEERS � PLaNNERS ' SURVEY❑Rs December i, 2011 Ms.Annette Lucas � NCDENR-Division af Water Quality 512 N. Salisbury Street Raleigh, NC 27626 Re: Ashton Hall Subdivision — Phases 3 &4 Durham, NC DWQ Praject#ob-za42 v.3 W&R Project#ozo9o5o0.0 Dear Ms. Lucas: Please find attached three (3) copres of Diffuse Flow Plans and supporting dacuments for the above- referenced project. This information is provided in respanse ta your November 22, 2011 letter requesting additional information. The additional information requested is listed below,followed by a written response: Additianal fnformatron Requested.• .t. Please provide one Leve/ Spreader 5upplement Form for each proposed leve/ spreader, avai/able athtt : ortal.ncdenr.or,g/web/w4fws/sufbmp-manual. Please 1nc/ude the required items check/ist and al!items listed therer"n. Response: Included with this submittal are three (3) copies each of the following documents: • Diffuse Flow Plans (13 sheets); • Stormwater Impact Analysis Memorandum (3 pages); • Flow Splitter Worksheets (3 pages}i • Plunge Basin Dissipator Report (1 page); • Leve[ Spreader-Vegetated Filter Strip Supplement (one supplement each, far all three level spreaders-9 pages total); • FilterStrip, Restored Riparian Bufferand Level SpreaderOperation&MaintenanceAgreements (one each, for all three level spreaders — 9 pages total). If you need any additional info�rn��,�;�i��,��y questions, please give me a call at g7g-469-3340• �� }�� , � .# Sincerely, ��;.. � � WITHERS �V��L*� �F �} � � �,. ; r � �•{ �' �� }� `'> ' � I��d�� *.�t � �� }Y"�+ 4 Y ��°�I��f . ��t �� %,� � � �„ � , r.„ � . r�. c�* Patrmck Allen ��z��H�rn�� r�. '•, file xix MacKenan Drive f Cary,NC z75iz I te(:9s9�469•334a I faxc9i9,238.zogg� .w�thersravenel.com zqzo Commonwea{th RrEVe�Suite iox�Wifmington,NC z8r�o3�tel:9io.z56.gz77 I fax.qxa.256.258t� qi6 D Gat(imore Dairy Road � Greensbaro,NC 27409 � tel:33b-993-55a4 i Praject Qes�rip�i.an Solve For �3��c��r�� InpUt;Crafa Headwater Elevation 347.12 ft Centroid Elevation 346.15 ft Tailwater Elevatian 345.8q ft Discharge Caefficient 0.60 Diameter 6.00 i� t'SU��S discharge [�.�� #�� Headwater tieight Above Centroid 0.97 ft Teilwater Height Aboue Centroid -0.35 ft Flow Area 0.20 ftz Velocity 4.74 ftls Bentiey Systems,Inc. Haestad Methods Solufian Center Bentley FlowMaster [48.01.071.00] 11130t2011 12:02:44 PM 27 Siemons Company Drive Suite 260 W Watertown,CT 08795 USA +1-2Q3-755-1666 Page 1 of 1 1 Project Descri�tic�r� Salve Far �i��h��°�� T1�U�,��t� Headwater Elevation 359,73 ft Centroid Elevatfon 359.05 ft Tailwater Elevation 358.70 ft Discharge Coefficient 0.60 Diameter 6.04 �t� E;.ESGI� Discharge ��'�� f� Headwater Ffeight Above Centroid 0.68 ft Tailwater Height Above Centroid -Q.35 ft Flow Area 0.20 ftZ Veloci#y 3.97 f#is Bentley 3ystems,Inc. Haeskad Methods Solution Center Benttey F9owMaster [08.01.071.Q0] 11l30l2011 12:02:17 PM 27 Siemons Company Qrive Suike 200 W Watertown,CT 06795 USA +1-243-755-166& Page 1 af 1 1 P�aject Des�ripfiian Solve For C�r`s�Yr�� tpU�� Headwater Elevation 380.25 ft Centroid Elevation 379.25 ft Tailwater Elevation 378.95 ft Discharge Goefficient 0.60 Diameter 6.d0 °is� F��UG#S Discherge �3•�� f� Neadwater Height Above Centroid 1.OQ ft Tailwater Height Rbove Centrold -Q.30 ft Flow Area 0.2d it2 Velocity 4.84 ftls Bentley Syskems,tnc. Fiaestad Methads Solution Center Bentley FlowMaster [08.01.079.00] 19t3012011 12:02:47 PM 27 Siemons Company Qrive 3uite 200 W Watertown,CT q6795 U5A +7_p03-755-1666 Page 1 of 1 � r��- �8 �* �* eei �'"�. . ��. rvx '� :.; :: � � �, , � � �' ' �. � �' *�t� 4r �€ti#` � `._ ::::° �Sa s� �,' � ', , ,....: . �s. u: ' � �; ;.., _ c �...��,;.,;;,,;,,, ya: �. � ..::: '..,',.-,`?; �3 � �: ....... .. �'a C".x �"a , a° e— .. .... . �.. t, �:s �� C,b. � �.,.. ..:�..:.... ." �� ,b ��.� cs� ....�:._..:��. ':-. �'y. q'y .t`.is s�. :.;.,.�:��,,,. . .. .... � � ata ��..�... ': '.; � � � � � ..;..: i .,��:I #t ... �', � � � `��'�::i >�� ,��. � � � I�k�4q � i ... ... � tiJF�4' 2, 3 z ��. F- AIRt. � P :� �.. I1Ye� � r V �:. i Z � ��,.,. �� .. � � 6�N6�: �� .. � J � � �y 3�. � �"". � �. � ,� �"'. �� Y... � �.� J}# :: .'�'£ � ... . �. ii� ix� � ��. � �� r �� " � �., :GiE`�� suw �'�«��,�, � +�. . ?,:.��x-Yi � ��. � � A �* ��,�� d.�7 �°9� 'w �.: � �i �g�,:E. ..v,:' � i'V�,� � �; a� � �7 � � � , �r s � �'� �.':�.: �' � � � `;��n" � � �..,s�� x �., � � ��,� � � r, � �:� �� as �� °i � �� N � �W �.�v, r�� -� � � � � �z � �s � � :��. � � � ,� s #�} �� ,� ,� � � �t �d7 C�i �w £�.'�t�: � �1 �� . ��.� ��. ��.��. � ��. ��.. . �'t, C3i E�. � Permit Number: ' (to be provided by DWQ) Drainage Area Number: �%YJf'�,�4�� I �P 1 r eS� I'f.' 1 1'1 �' V � T c� C'TC �' 1 1 f� Ce ee e �' I will keep a rnaintenance record on this BMP. °s m ' ten ce record wi11 be kept in a log in a known set lacation. Any deficaent BMP elements noted in the inspection w�11 be corrected,repaired or replaced i ediately. These deficiencies c affect the ' tegrity af structures,safety of the public, d e removal efficiency of the BMP. I partant aintenance procedures: — Immediately after e filter strip is established, y newly planted vegetat7an will be watered twice weekly xf needed til e plants becorne established {co anly six weeks). — C�nce a year, the filter strrp w�11 be reseeded ta maintain a dense growth of vegetation — �fable groundcover will be maintained in the drainage area ta reduce the sediment load ta the vegetation. — Twa ta three times a year, grass filter strips w�ll be mawed and the clippings harvested ta pxomote e growth of thick vegetatian with optimum pollut t removal efficiency. Turf grass shauld not be cut shorter�han 3 to 5 inches and may be a owed ta grow as tall as 22 inches depending on aeskhetic require ents (NIPC,1993). Forested filter strips do nof require °s fype af m " tenance. — Once a year,the soil will be aerated i£necessary. — Once a year, soil pH wilt be tested d ` e will be added if necessary. After the fzlter skrip is established,it will be inspected quarterly and it in 24 o s after eve sta event eater t an 1.Q inc (or 1.5 inc es i�in a Caastal Coun ). Recards of operatian and ainten ce wi11 be kept in a awn set location and will be available upan request. Inspectian activities shall be performed as follows. y prable at are found shail be repaired immediately. 'B P ele enf: 'PotenEial rable : ow I will remediate the rablem; The entire filter strip Trash j debris is present. Remove the trash j debris. s stem The flow splitter device The flow splitter device is Unclog the conveyance and dispose '{if applicable) 'clo ed. of an sediment off-site. 'The flaw spiitter device is ' Make any necessary repairs or damaged. replace if ciamage is toa large Eor re air. Form SWU401-Level Spreader,Filter Strip,Restored Riparian Buffer O&M-Rev3 Page 1 of 3 B P e1e ent: ' Patential rablern: How I will remediate the roble : '' ' The swale and the level The swale is clogged with 'Remove the sedirnent and dispose lip sediment. a�it off-site, - The Ievel iip is cr°acked, Repair or replace lip. settled,undercut,eroded or okFierwise dama ed. There is erosian around the Regrade the soYl to crcate a berm end af the level spreader that that is higher than the Ievel lip,and shows stormwater has 'then plank a graund cavex and bypassed it. water until it is estabiished. Pravide lime and a one-kime ferkilizer a lication. Trees or shrubs have begun Remove them. ' to grow on the swale or just downslo e of the level li . The bypass channel ' Areas of bare soil and jor Regrade e sail if necessary to ' erosive gullies have formed. remove the gully,and then reestablish ra er erosion contral, ' Turf re' orcement is Study the site ta see if a larger damaged ar ripap is rolling bypass channel is needed(enlarge if dow iil. necessary). After thas,reestablish e erasion control material. The filter strip Grass is too shart or too lang Maintain grass at a heaght of ' if a licable . 'a rox° atel three ta six inches. ' Areas of bare soil and/or Regrade the soil if necessary to ' erosive gullies have formed. ' remove the gully,and then plant a ', ground caver and watex until it is ' established. Pravide lime and a one-t�me fert�3izer a Iication. Sed°unent is bu�Iding up an Remove the sedi ent and t�e filter sfrip. restabiiize the sail with vegetafion if necessary. Provide Iime and a one- ° e fer ' ' er a licafion. Plants are desiccated. Provide additional irrigation and ' fer ° ' er as needed. ' Piants are dead,diseased or Determine the source of the dying. problem: soils,hydrology,disease, ' etc. Remedy the problem and ' replace plants. Provide a one-time fertilizer a licaEian. Nuisance vegetatian is Re ave vegetaNan by hand if choking out desirable species. 'possible. If pesticide is used,do not allaw it to get into the receiving ' water. The xeceiving water Erosion or other signs of Contack the NC Division of Water damage have accurred at the Qualify local Regional Office,or the outlet. 401 Oversi ht LJrut at 919-733-1786. Form SWU401-Level Spreader,Filter Strip,Restored Riparian Buffer C?&M-Rev.3 Page 2 of 3 Permit Number: � (to be�arovided by DWQ) I acknawledge and agree by my signature beiow that I am respansible for the perfo ance of the maintenance procedures listed above. I agree ta notify DWQ of any prabiems with the system or prior to any changes to the system nr respansible party. Pr°oject name: Ashton all - Phases 3 & 4 BMI' c�rainage area number; BMP#7 Print n�z7.��9 "T� Sc.�2.rrn2�-h.t'�rrl, Title. r� Address: � ��" �°�°� �.:�'�.� ��.� �� 2'1G 12 Phone: t t _ ��a�t�r�a _ Date, �� t t NOte: TI1e legaliy responsible party should nat be a homeowners association unless mUre than SO°lo of the lots have been sold and a a°esident of the subdivisian has been named the president. I, �.�`��"°� *�� ' ,a Notary Public for the State of � �� , Caunty of , do hereby certify th�t personally appeared before e this �` day of � - � , �� '- , d acknowledge the due execu�ion of the forgoing filter strip, riparian buffer, and/ar level spreader maintenance requirements. Witness my hand d official seal, 41111i1lJ �.�. ��*�� '+�' � � � �! � � m .°' � ��+�� a � � � � � �` *�,� w*dx e '�x �� : �� o-�� y cammission expires 4� t � � i'or�n SWU401-Level Spreader,Filter Strip,Rcstored Riparian Buffer O&M-Rev.3 Page 3 of 3 Permit Number: (to be provided by DYYQ) Drainage Area Number: P, fv i t i , es r i ari r evel re er erati ai e ce e e I will keep a m ° tenance record on this BMP. is rnainten ce recoxd will be kept ' a log�n a own set location. y deficient BMP elemenfis noted in the inspection will be ' corrected,repaired ar xeplaced immediately. These deficiencies can affect the integrity ' of structures, safety of the public, d the removal efficiency of the BMP. Irnportant maintenance procedures: — I ediately after the filter sfrip is established,any newly pl t�d vegetai�on will be watered twice weekly if needed til the pl ts become established (co anly six weeks). — Once a year,the f°rlter strip wi11 be reseeded ta maintain a dense gxawth af vegetatian — Stable groundcover w�ll be maintained in the drainage area to reduce the sedi ent load to c vegetation. — Two to ee tsmes a year, grass f�lter stY'rps will be mowed d e clipp° gs harvested tt�promote the grawth af °ck vegetation with aptimum pallutant re oval efficiency. Turf grass should nof be cufi shorter th 3 ta 5 ° ches d ay be allowed ta grow as tall as 12 inches depending on aes etic requirements (NIPC, 1993).Forested filtex strips do not require is type of maintenance. — Once a year,the sail will be aerated if necessary. — Once a year,sail pH will be tested d lime will be added�f necessary. After the filter strip is established,it will be inspected uarterly an it in 24 aurs ter every sta event eater t an 1A inc (or 1.5 inc es if in a Coastal Caun ). Records of operatian and ainten ce will be kept in a own set Iocatian and w�il be ava�Iable upon request. Inspection activities shall be performed as follows. y prablems I-hat are found shall be repaixed immediately. P element: Potential roblem. ow I will re ediate the roble : The enfire£i]ter strip Trashjdebris is present. Reznove khe trashjdebris. s ste The flaw splitter device The flow splitter device is Unclog the conveyance and dispose ', (if applicable} cla ed. of an sed° ent off-szte. ' The flow splitter device is 'Make any necessary repairs ar damaged. 'replace if damage is toa large for re air. Form SWIJ401-Level Spreader,Filter Strip,Restored Riparian Buffer U&M-Rev3 Pagc 1 of 3 ' BMP elemenEc Potential rable : ow I wi11 re ediate the roblezn: The swale and the level The swale is clogged with Remove the sediment and dispose ' lip sediment. af it off-site. ', The Ievcl lip is cracked, Repair or replace Iip. ' settled,undercut,eraded or , ' atherwise darna ed. ' ' There is erosion around the Regrade the soil to create a berm ' end of the level spreader that ' that is higher than the level lip,and ' ' shows stormwater has 'then piant a ground cover and ' , bypassed it. water until it is established. Provide ' ' ' lime and a one-time fertilizer ' a licatian. ' Trees or s}Zrubs have begun Remove them. to grow on the swale or just ' downslo e of thc level li . The bypass channel Areas af bare sai]and/or Regxade Ehe soil if necessary to erosive guilies have farmed. remove the gully,and then reestablish ra er erosian cantrola Turf re' orcement is Study the site ta see if a larger damaged or ripap is rolling bypass channel is needed{enlarge if dow ill. necessary). After ° ,reestablish the erosion control material. The filter sErip ' Grass is too shart or tao long Maintair7 grass at a height of if a licable . a roximatcl three to si�c inches. Areas of bare soil and f or ' Regrade the soil if necessary to ' erosive gullies have formed. ''remove the gully,and then plant a ground cover and water until it is estabiished. Provide lime and a 'ane-time fertilizer a licatian. Sediment is buiiding up an Remave the sediment and e fil:ker strip. restabilrze e sail with vegetatzan if necessary. Provide ' e and a one- time fer ' ` er a lication. Plants are desiccated. Pravide additional�rigation and £er ' ' �r as needed, Plants are dead,diseased or ' Determine the source af the dying. ' prablem: soils,hydrology,disease, etc. Rernedy the problem and replace plants. Provide a one-time 'fertilizer a lication. ' Nuisance vegetation is Remave vegetation by hand if choking out desirable species. possible. If pesticide is used,do not a]]ow it ta get ulto the receiving vvater. The receiving watex ' Erosion or other signs of Caz�tact the NC Division of Water damage have occurred at the ; Qualify local Regional Office,or the ' outlet. ' 401 Oversi ht Unit at 919-733-1786. Form SWU401-Level Spreader,Filter Strip,Restored Riparian Buffer U&M-Rev.3 Page 2 of 3 Permit Number: (to he provicled by DWQ) I acknowledge and agree by my signature below that I am responsible for the perfo ance of the maintenance pracedures lzsted above. I agree to notify DWQ af any problems with the system or priar to any cl�anges to the system ar responsible party. Project name: Ashton Hall - Phases 3 & 4 13MP d�°ainage a�ea numbe�^: B P#10 �r��t �� ' ''� �� Title: �* , � �` `°'� , 1�ddress: �� ¢��.,�� #:�. �� , �� ,, �,C. 2'"�+�12. Phone: � � - Signature: � � { ' Date: � � t � Note: The legally responsible parky shauld not be a hameawners association unless more than 50°lo af the lats have been sold and a resident of the subdivision has been named the president. I, `--�°" �' � �� ' „ ,,,, a Notary Public for the State of 1 i , County of �. , da hereby certify that Tt�r,� 'S�c. u +� c�� personally appeared before rne this »��' day af- , t , and ac owledge the due execution af the forgoing filter strip, riparian buffer, and/or level spreader maintenance requirements. Witness my hand and official seal, ��q,i�1��1111��t, `,,�,v�° $. G`,[j�,+��,�r�'. _ � r : ��' � � = � ��°� : _ : , : :'� � ° �' ci.= ..,�.�� ,�`�. ., ` `� s�,� ``' �°��+rtrtf�tt`rt``` SEAL # My commissian expires 1 �- t C� � �� Form S 461-Level Spreader,Filter Strip,Restared Riparian Buffer O&M-Rev.3 Page 3 of 3 Permit Number; (ta b�provided by DWQ) Draznage Area Number: N• %f I �T 1 , eSf 1 �'Ia � E'�' E.'VE' �'t' Y' e�' �1 1 � C � f I will keep a maintenance record on this BMP. "s mainten ce recard will be kept in a Iog ir� a known set location. Any deficient B P elements nated ' the inspection wi11 be carrected,repaired or replaced ° e `ately. These deficiencies can affect the integrity of structures,safefy of the public, ana fhe removal efficiency of the BMP. Importanf ma° ten ce pracedures: — I ediately after the filter strip is established, y newly planted vegetation will be watered ice weekly if needed until the plants becorne established (co only six weeks}. — Once a year, the filter stri�will be reseeded ta aintain a dense growth af vegetation — Stable graundcover will be mau�taaned in the drainage area to reduce the sediment load ta e vegetation — Two to three times a year, grass filter strips will be mowed d the clippings harvested to promote e growth af t °ck vegetation wath optimum pollut t removal efficiency. Turf grass should not be cut shorter th 3 to 5 inches and ay be allowed to graw as tall as 12 inches depending an aesthetic requirements (NIPC,2993). Forested filter strips do not requxre ;s type of mainten ce. — Once a year,the soil w" be aerated if necessary. — Onc�a year,soil pH will be tested d lime w�ll be added if necessaxy. After the filter strip is established,it will be irtspected uarterly and ithin 24 ours ter eve stor event eater t an 1.0 inc {or 1.5 inches if in a Coastal Counfy}. Records of operation and xnaintenance wi1l be kept in a known set Iocatian and will be available upan request. Inspection activities shall be perfor ed as follows. y proble that are found sha11 be repaired im ediately. B P e1e ent: Pakenkial rc�blem:- ow I will remediate the roblem: 'The entire filter strip `I'rashJdebris ispresent. Remave the trash/debris. s stem The flow splitter device The flow splstter device is Unclog the conveyance and dispose (if applicable) clo ed, of an sed°unent off-site. The flow splitter device is Make any necessary reparrs or damaged. replace if damage is tao large far C� aII'. Farm SWU401-Level Spreader,Filter Strip,Restored Riparian Buffer O&M-Rev.3 Page 1 af 3 P e1e enk: ' Potential roble : ow I will re ediate the rable c The swale and the Ievel ' The swale is clogged with Remove the sediment and dispose Iip sedimenf. of'rt aff-site. ' The level lip is cracked, Repair or replace lip. settled,undercut,exoded or otherwise dama ed. ' There is erosian around the Regrade khe soil to create a berm ' end of the level spreader that ' that is higher than th�Ievel Iip,and ' shows stormwater has ' then plant a ground cover and ', bypassed it. 'water until it is established. Provide lime and a ane-time fextilizer ' a lication. Trees or shrubs have begun Remove fihem. to grow on the swale or just ' davvnslo e of the ievel li . The bypass channel Areas of bare sail and jor Regrade the soil if necessary to erosive gullies have formed. remove the gully,and then '' reestablish ro ex erosion cantrol. ' Turf reinforcement is ''Study the site to see if a larger ' darnaged or ripap is rolling bypass channel is needed (eniarge if downhill. necessary). After this,xeestablish e erosian control material. The filter strip Grass is toa short ar tao Iang Maintain grass at a height of ' if a Iicable). a roximatel _three ta six inches. l�reas of bare soil andJor Regrade e soil if necessary to e2°asive gullies have formed. remove the gully,and then plant a ground cover and water until it is established. Pravide lime and a one-time fextilYZex a l�cat�on. Sed�ment is bu�lding up on Remove the sed°amenE and ' the fslter strip. resEabilize the soii with vegetation 7f 'ziecessary. Pravide lime and a one- ' time fertilizer a Iication. 'Plants are desiccated. Pravide additional irrigation and '#ertili�ex as needed. ' Plants are dead, diseased csr Determine the source of the ' dying. ' praUlem: soits,hydrolagy,disease, ' etc. Remedy the problem and ' replace plants. Provide a one-time fertilizer a licatioz�. Nuisa��ce vegetation is Remove vegetat�on by hand if chaking out desirable species. possible. If pesticade is used, do nat allow it to get into the receiving ' water. The receiving water Erosion or other signs af Contact khe NC Division of Water ' damage have occurred at the ' Quality Iocal Regional Office,or the ' outlet. ' 401 C}versi ht Unit at 919-733-1786. Form S W U4d 1-I,evel Spreader,Filter Strip,Restored Riparian Buffer O&M-Rev3 Page 2 of 3 Permit Number: (to be pravided by DWQ) I acicnowledge and agree by my signature below that I am respar�sible for the performance af the maintenance procedures listed above. I agree to notify DWQ of any problems with the system ar prior to any changes to the system or responsible party, Project name: ��t�r��-T�I� �1�� BMP dr�ainage ar�ea number°: ��'�1�'' Print name: Title. �'� �`�- i Address: � r , g Phone: ��'i �� 4�3$1 — 35t� rfr Signature: Date: � � �� [ � Note: The legaliy respansibie party should not be a homeowners association unless more than 50%af the lots have been sald and a resident af the subdivision has been named the president. I, "��-�'�- � • � � �� a Natary Public for the State c�f � , County of do hereby certify that � �°` ' �° '��` personally appeared before me this,�� day of �� , �� ,> and acknowledge the due execution of the forgaing filter strip, riparian buffer, and/or level spreader mainten ce requirements. Witness my hand and official seal, ��,�,��t,�� ,�� . �� '�,�, � �� ,�, � � �` � ��. � � �, � �� # � �� *�� `'�rrrr� s��t��*�� SEAL w�'��. My cammission expires , " �� Form S 401-Level Spreader,Filter Strip,Restored Riparian Buffer O&M-Rev.3 Page 3 of 3 ��r�� STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLIGATION FORM LEVEL P E -V T T ILT T IR(L -VF ) U PLE T Tfrr°�f�rr�a rrru�f b��r��1�t�ly fFJl�c��tr��r�rrf�d,Frai��aJ�d,�r�d�a�brrad�f�d, L ��'!:�OR TIQN Project name Ashtan Hall-Phases 3&4 Contact name Brad Hart,PE-Withers&Ravenei,inc. Phone number (919)469-3340 Qate November 30,2011 Drainage area number BMP#7 #�� [��I��i��II�TI�N The purpose of the LS-VFS Bufier Rule: Qiffuse Flow ` Starmwater enters LS-VFS from A 8MP' Type of VFS Engineered filter strip(graded&sodded,s14pe z 8°�) Explanation af any"Other"responses above If Stormwater Enters the L3-VFS from the Drainage Area Drainage area , {� ��r��t c�re�pl�',�lh�i��i��r��;f t'��form. Pmpervious surface area ` {� D�r�;t c:�,Y7�I€��t3�;��flrti�r��i��f� , Percent impervious °fa G�ri�E�;ra,��l�°�t?�6s��t;�r��ih�f�, Rational C coefficient ��,�;�q��;��;��;��;�;�f�, Peak flow from the 1 inlhr storm �{s ��;��p�i;;E��,f��g� Time of concentration min C��n�i r.�mp,ete�hi�secti��c��h�3�,.. Rainfall intensity,10-yr storm inlhr D��g°c�mp:�t�:hi�s ��:��€E�� ,:. Peak flow from the 30-yr storm cfs D��ct�am�e��ihis:��ii��G€the�� ,. Design starm Maximum amount of flow directed to the LS-VFS cfs ��r:ffP;�r��lAte this sp€.ii�r c�t��tr�. is a flow bypass system going to be used? {Y or N) �o not complete this section ofi#he fo . Explanation of any"Other"respanses above If Stormwater Enters the LS-VFS fram a BMP Type of 8MP Wet detention pontl Peak discharge from the BMP during the design storm 4p.�5 ' cfs Peak discharge from the BMP dunng the 10-year storm �g,4� ' cfs Maximum capacity of a 10d-foot long LS-VFS 10 cfs Peak Ilow directed to the LS-VFS Q,93 ; c{$ is a flow bypass system gaing ta ba used? 'Y `, (Y ar N}; Explanation of any"Other"responses above LS-VFS Design Farebay suriace area 'sq� Depth of forebay at stortnwater entry paint ''i� Depth of forebay et stormwater exit point '�n Feet of level lip needed per cis 1 Q fUcfs Computed minimum leragth of the level lip needed 9 ft Ten feet is the minimum level spreader length. Length af level fip provided 't0 ft Width of VFS 30 ft Elevation at downslope base of level lip 346��fl ''fmsl Elevation at the end af the VFS that is farthest from the L5 344.7fl ''fmsl Form SW401-LS-VFS-27Juf2011-Rev,9 page 1 of 3 Siope{fram levei lip ta the end oI the VFS} 4,33 % Are any draws present in the VFS? ' !� ' {Y or N) OK Is there a callector swale at the end of the VFS? '' {� ' (Y ar N) Bypass System Design{if applicabie) Is a bypass system provided? ' 1' ' (Y or N) Is there an engineered flow splitting device? 1' (Y ar N) ��e��p��id��iar de#��I��a��litt�r�sa��r:i°��c�?cs. Dimensions of the channel(see diagram belaw): M ?,04 ' 'ft B 10.�U '' 'ft W 16.00 '' 'ft y(flow depth for 10-year storm) '1,03 'ft {reeboard{during the 1Q-year storm} 0.47 ft Peovide ai least one foat of ir��board. Peak velocity in the channel during the 10-yr storm 2.37 ' ftlsec Channel lining material Pick one: Does the bypass discharge through a wetland? '�! ' '(Y or N) Does the channel enter the stream at an angle? N1A ', ,{Y or N} Explanation of any"Other"responses above Plunge 8asin provided below 6ypass outlet 8�upstream of npanan buffer. 1�' # � { �, t< ; � #z��tr��e�l��d x tl��1 �-�••;�t��Y�� } 4 ; }�t�iurirt�Il��14-}•r,toizti� t E �� _ -� � �f �S } k... ..... ,.,.k.. � � J ��1. REQUIR�d ITE S CHECKLIST EDIT Please indicate#he page ar plan sheet numbers where the supporting documentation can be faund. An incomplete submittal package will result in a request for additional infarmation. This will delay final review and approval of the project. Initial in the space provided to indicate the foliowing design requirements have been met. If the applicant has tlesignated an agent,the agent may initiai befow. If a requirement has nat been met,attach Justification. Requried Item: E �#��1� Page or plan sheet number and any notes: 1. Pians(1"-50'or larger)of the entire site showing: ' ;8heets'4.1,4.2,8.1,8.2 -Design at ultimate buiid-out, ; -Off-site drainage{if applicable), -Qelineated drainage basins(include Rationai C coefficient per basin), -Forebay(if applicable}, -High flaw bypass system, -Maintenance access, -Proposed drainage easement and public right of way(ROW),and -Boundaries of drainage easement. i ' 2. PPan details(1"=30'or larger)for the level spreader showing: (Sheets'8.1,8.2,1t�.2 -Forebay(if applicable), i -High flow bypass system, -One foot topo lines between the level lip and top of stream bank, -Proposed drainage easement,and -Design at ultimate buiid-out. Form SW401-LS-VFS-27Ju1201 f-Rev,9 page 2 of 3 3. Section view of the level spreader(1'=20'or larger)showing: �t��.'E,"#�,� -Underdrain system{if applicable), -Level lip, ' -Upslope channel,and ' -Downslope filter fabnc. ' 4. Plan details of the flow splitting device and supporting calculations{if applicable). ;�h�#�,� 5. A construction sequence that shows how the level spreader will be protected from $�l�� sediment until the entire drainage area is stabilized. 6. If a non-engineered VFS is being used,then provide a phatagraph of the VFS showing :�ldA -'- that no draws are present. 7. Ths supporting caiculations. 8. A copy af the signed and notarized operation and maintenance(0&M}agreement � Form SW401-LS-VFS-27Ju12011-Rau.9 page 3 of 3 �� STORMWATER MANAGEMENT PERMIT APPLICATION FORM 401 CERTIFICATION APPLICATION FQRM L V L P -V T T FILT T IP(L -VF j PPL T ThF�f�rrrt r��r�t 6��r�rpf�f�Jy�tl�d�crf�p�Frrt�d,Frai�ia��d,�r�d�c�br�a�t�d. �� P� �� "�1 F R A'�1 N Project name Ashtfln Hali-Phases 3&4 Contaet name Brad Hart,PE-Withers&Ravenel,Ine. Phone number (919}469�3340 Date November 3Q,2011 Drainage area number BMP#10 II� ��It��1��#��t�►T��1 The pu�pose of the LS-VFS Buffer Rule: diffuse Elow ' Stormwater enters LS-VFS from A BMP'' Type af VFS Engineered fifter strip(graded&sodded,slope<8°l0) Explanatian of any"Other"responses above if Stormwater Enters the LS-VFS from the Drainage Area Drainage area {� ��r��t�omaEe?e this us:iic�s�cf t��f�, . impervious surface area � ��n�t�sa��Ea:�this s�uti�r�cf fn�fi�:��. Aercent impervious °!o G�r��t co�n�E�;�this�evti�r��e��, . Rational G coefficient G�r��E c:sft�pE�,�fhis��cCi�re�C 4��C�, . Peak flow from the 1 indhr storm cfs ��r r��i�;�rr��E�°��I�i�S�cli�r��f th�f�rr�;, Time af cancentration min ��n;�t c�s;n�I�°�this��c�i�n r�{;t,�f;�, , Rainfali intensity,10-yr storm inlhr G�n�t��npC�z�thi��cti�r��sh��, , Peak flow from the 10-yr storm cfs ��n�i��nple��this sa�t's�n�E zh�f�, . Design storm Maximum amount of flow directed to the LS-VFS ' 'cfs �a n�°��I�:�th;s s�et�r��f;��f�: . Is a Flow bypass system going to be used? �Y or N); ��n�:c�a��Ivt�Yh:s s?et:en�f�h�f�: , Explanation of any"Othe�'responses above If Stormwater Enters the LS-VFS from a BMP Type of BMP Wet tletention p4ntl Peak tlischar�e from the 8MP during the design starm 58.15 ' cfs Peak discharge from the BMP dunng the 1a-year storm 25.15 ' cfs' Maximum capacity of a 100-foot lang LS-VFS 14 cfs Peak flow directed to the LS-VFS 0.78 cfs Is a{fow bypass system gamg to be used? 'Y ' {Y or N) Explanation of any"Okhe�'responses above LS-VPS Design Forebay surface area sq ft Depth of forebay at stortnwater entry point '.in Depth of forebay at starmwater exit point ' in Feet of level lip needed per cfs 10 fftcfs Gomputed minimum length of the level lip needad � ft Ten feet is the minimum level spreader length. Length of level lip provided 1U ''ft Width of VFS '30 '''ft Elevation at downslope base of level lip 359.2fl ''fmsl Elevation at the end of the VFS that is farthest from the LS 358.5fl =-=-fmsl Form SW401-LS-VFS-27Ju12011-Rev.9 page 1 af 3 Slope(from levei lip to the end of the VFS) 2.33 °!o ', Are any draws present in the V�5? N , (Y or N) �i�: , is there a collector swale at the end of the VFS? ' N ,, (Y flr N} Bypass System Design(if appiicable) ' Is a bypass system provided? Y {Y or N) ' Is there an engineered flaw splitting device? Y (Y or N) Pl��se pr�r�sde p:an d�faiES�f 3;c�spl:iier��up��t�c��Ics: Dimensions of the channei{see diagram below}: ' M '2.00 ' ft B 10.OQ '' ft W 16.OQ '' ft y(flow depth far 10-year starm) D.98 ` ft freeboard{during the 10-year storm) 0.52 ` ft Prc+�id��°Ieast�rs��cf;r��ar�: Peak velacity in ths channe!dunng the 10-yr storm 2.14 ftlsec Ghannel lining makerial Picko�e: `Does the bypass discharge through a wetland? ` N s' (Y or N), Does the channei enter the siream at an angle? NIA ' {Y or N)' Explanation of any"Other"respanses abave Plunge'Basin provided belaw bypass outlet 8�upsVeam of ripanan buifer. �3'' � � , ; � , t � ti�abv<�tcl ale isa�d��lt��`�c�tvi�l}� � s �.i �� 1'{C�U1771,��1121{�-}'T.ro'CQll1T} � t � � �,.________ ��»��:_j �� Ai ..l�:...... �� .:K�. R �.l., ... ,:¢:... �': .�: .�;� ��8. �44dl8��Ea�I�L �Vrii.LALI�i EDIT Please intlicate the page or plan sheet numbers where#he supparting documentation can be found. An incomplete submittal package will result in a request for additional information. This wifl delay final review and approval of the project. Initial in the space provided to indicake the following design requirements have been met. If the appiicant has designatetl en agent,the agent may initial below. !f a requirement has not been met,attach justification. Requried Item: ��"�� t�plan sheet number and any nates: 1. Plans(1"-50'or larger)of the entire site showing: �.�h t��,2,8•5,8.6. -Design at ultimate build-aut, -Off-site drainage{if applicabie), -Delineated drainage basins(include Rational C coefficient per basin), -Forebay(if applicable), -High flow bypass system, -Maintenance access, -Proposed drainage easement and public right of way(RQW),and -Boundaries of drainage easement. 2. Plan details(1"=30°ar larger)for the level spreader showing. � iShee�8.5,8.8,10.2 -Forebay{if applicable), -High flow bypass system, -One foot topo lines between the level lip and tap of stream bank, -Proposed drainage easement,and -Design at ultimate buiid-out. Form SW401-LS-VFS-27Ju12011-Rev.9 page 2 of 3 3. Section view bf the level spreader(1"=20'ar larger)showing. ;��5�.�.��.�; -Underdrain system(ff applicatile), -Level lip, � -Upslope ohannel,and -Downslape filter fabnc. � � , 4. P(an details of the flow splitting device and suppo�ing calculations(if applicable). SM��,� � ' 5. A constn�ctian sequence that shows how the level spreader will be proteeted from ��.� sediment until the entir�drainage area is sfabiPized. # 6. If a non-engineered VFS is being used,then pravide a photagraph of the VFS showing ;P�dA that no draws are present. 7. The suppo�ing calculations. 8. A copy af the signed and notanzed operation and maintenance(0&M)agreement. Form SW401-LS-VFS-27Ju12011-Rev:9 page 3 of 3 �� ` �� a � �. �� a �' ' �� STORMWATER MANAGEMENT PERMfT APPLICATION F4RM 401 CERTIFICATION APPLICATIQN FORM L L T T ILT I (L - F ) L T Tba�f�rrr�rr�c��b��r�ap1�#�iy fr11��u�,prir�#�d,iraiti�l�d,�rad�cabrrrc�t�da �. PROJ CT I FO A"�IQN Project name Ashton`Hali-Phases 3&4 ` Contact name Brad Hart,PE-Withers&Rauenel,inc. Phone number (919}469-3340 ` Date November 30,2011 Drainage area number BMP#11 #1. ��!I F�R �`I��t The purpose of the LS-VFS Buffer Rule: Diffuse Flow Stormwater enters LS-VFS from A BMP'' Type of VFS Engineered fiiter strip(graded&sodded,slape<8°la) Explanation of any"Other"responses above If Stormwater Enters the LS-VFS fram the Drainage Area Drainage area fC2 �c n�t c��pla.�this��i�r�f t��€crrn. Pmpervious surface area ft� Gc r��t��pl�tr�this��cii�r�cf t?�� . Percent impervious °to G�r��1�mpi�tr�this�ec[ia��t?��icrm. Rationai C coefficient ��;r�;�E�;�„7�I��is��cEiar��t�r��rm. Peak flow from the 1 indhr storm cfs ��n;�t��i€�§�kl�i�:��uki�r��;�lti�f�;rrr�. Time of concentration min [3�r��t��pi��khis��rki��E t��r E�;rrr�. Rainfall intensity,10-yr storm ` inthr C��n�t��~�plei�thi��c�ica€��E t?��frrr�. Peak flow fram the 10-yr storm cfs C�G n�t c�~�ple°�this��cki�€�cf t��c . Design storm Maximum amount of flow directed to the LS-VFS ` cfs C}c n�t c��I�:e�hi�sec`J��€t�e€� . Is a Flow bypass system going to be used? (Y or N) [?�nfft c��ci��e ihis:�c:ia�c€t?�e€�rm, Explanatian of any"Othe�responses above If Stormwater En#ers the LS-VFS from a 8MP Type of BMP Wet detenti4n pond Peak discharge from the BMP during the design storm 64,58 ' 'cfs Peak discharge from the BMP during the 10-year storm 42.27 cfs Maximum capaciiy of a 10Q-foot lang LS-VFS 10 cfs Peak flaw directed to the LS-VFS 0.95 cfs Is a flow bypass system going ta be usetl? ' Y ,, (Y or N) Explanation of any"Othe�'responses above LS•VFS Design Forebay surface area ,, ,sq ft Depth of forebay at stormwater entry point ` in Depth of forebay at stormwater exit point ``in Feet of levei lip needed per cfs 10 N/cfs Gomputed minimum length of the level lip needed 10 ft Ten feet is the minimum level spreader length. Length of level lip provided '10 'ft Width of VFS '30 '' 'ft Elevation at downslope base of levei lip 379.44 ''fmsl Elevation at the end of the VFS that is farthest from the LS 379.44 ' fmsl Form SW401-L8-VFS-27Ju12011-Rev.9 page 1 of 3 Slope{from level lip to the end of the VFS) 1.33 °/m Are any draws present in the VFS? ' �# (Y or N) �K Is there a collector swale at the end of the VFS? ' N (Y or N) Bypass System Design{if applicable) Is a bypass system provided? ' Y ' (Y or N) Is there an engineered flow splitting device? Y {Y or N) .�I��s��rt��i��pl�r�z��i�;l��?1��r r>�lit��r F�;�G��;�rlir;�;�I�M}, Dimensions af the channel(see diagram below): M '2.�0 ''°'ft B 1{I.QQ ' ft W 16.00 ft y(flow depth for 10-year storm) 1.�7 ft freeboartl(during the 10-year storm) 0:33 ft �re�:de ai Iuas?��e€a�t��€ree�aar�;, Peak velocity in the channel during the 10-yr storm '2�94 ' '�/sec Channel lining material Pickone: Does the bypass discharge through a wetiand? ' � ' (Y or N) Does the channef enter the stream at an angle? 'N/A ' (Y or N) Explanation of any"Other"responses abave Plunge'Basin provided below bypass outlet&upstream of riparian buffer. tit' p,. ... ..... ..... ..... ......... .. ..... ... ... ... .... .... ..�.. � t g ti y i' �C�:��i� d�4�[lIi' �� {?"i' :i#4?[1 a d � �(ctunit�the [4=}'r ytcsnul ; � ;,:r:_____ �..��..��..$. � [+[ Af t ; F; � �F �' .� II�. REQUIRED iTEMS CHECKLIST EDIT Please indicate the page or plan sheet numbers where the supporting documentation can ba found. An incomplete submittal package will result in a request for additional informatian. This will delay finai review and appraval of the praject. initiai in the space provided to indicate the following design requirements have been met, if the appiicant has designated an agenf,the agent mey initial below. if a requirement has not been met,attach justificatfon. Requried Item: � ��g��C pl��a��r�u�tb��nd�tty��te�; 1. Plans(1"-5Q'or larger}of the entire site showing: :� �4.�,9.�,�,T��r� -Design at ulkimate build-out, -Off-site drainage{if applicable), -Delineated drainage basins(include Rational C caefficient per basin), -Forebay(iF appiicabie}, -High flow bypass system, -Maintenance access, -Proposed drainage easement and public right of way(ROW),and -Boundaries of drainage easement. 2. Pian details(1"=30'or largerj for the level spreader showing: � :Sheets 8.7,8.8,10.2 -Forebay(if applicabie), -High flow bypass system, -dne foot topo lines between the leuei lip and top of stream bank, -Proposed drainage easement,and -Design at ultimate build-aut. Form SW401-LS-VFS-27Ju12011-Reu.9 page 2 of 3 3. Secfion view 4f t�e level spreader(1"=20'or larger)showing: ,�P� �,�,��.� -Underdrain system{if applicable), -Level lip, -Upslope channel,and -Downslape fifter fabric. 4. Plan details of the flow splitting device and supporting calculations{if applicable). ;� ��.7 5. A construction sequence that shows how the level spreader will be pratected from '��,7 sediment until the entire drainage area is stabilized. 6. If a nan-engineered VFS is being used,then provide a photograph af the VFS showing :Nf� that no draws are present. 7, Tha supporting ealculations. &. A copy of the signed and notarized operation and maintenance(0&M}agreement. Farm 5W401-LS-VFS-27Ju12011-Rev,9 page 3 of 3 t c-saa ' ENG,NEERS ' P�.ANNERS � SURVEY��s ' a � � �, . *��d��a � � �� TU: Ragh u Badami, PE ,��,'� �a�� r City af Durham '` ¢"" � � m¢: Stormwater Services Department ��' �' ��w � � � � �' � � F . Hunter Freerrran PE � � � �� '�,'��'� 4' � � � �� CC: Brad Hart, file ��`��`��"�¢�"��`' � � ° � � ��J�i`�1�� ATE: Octaber 18, 2011 SU JE . Ashton Hall — Phases 3 & 4 (Previous Case # D0800057) Stormwater Impact Analysis- Revised Withers & Ravenel has campleted a hydraulic study af the revised site plans for the above referenced site. A stormwater impact analysis, prepared by Chas. H. Sells Inc. was previously approved by Durham. Withers & Ravenel has assumed design responsibility far phases 3 and 4 of the Ashton Hall subdivision. In the previously approved SIA, these phases included designs for 5 wet detention ponds. These 5 basins were referred ta as basins 5, 7A, 7B, 7C, and 1Q in the original SfA. Four {4) wet detention ponds are praposed (BMP#7, 8, 10, & 11) with level spreaders installed upslope of Neuse River Buffers in accordance with State and local ordinances. Watershed basins 5 and 7B have been cambined from the approved SIA have been combined and the runaff from these watersheds now flows into one SMP. Pond routings completed by Withers & Ravenel indicate that the major design eiements of the previously appraved SIA, including structural design efements, water quality treatment, and peak flow attenuation can be achieved with the current site plan. BMP sizing and pond routing calculations are attached to this memorandum. 7he primary outlet structure for each pond consists of a precast concrete inlet box riser with a 2" diameter water quality drawdawn device to provide water quality treatment and extended drawdawn of the runoff generated by the first 1" of runaff. The entire water quaiity valume will flow wif! be diverted to the level spreaders. The riser structures are designed to split the flow per the guidelines in the current version of the NC DWQ BMP Design Manual. The peak flow to each af the level spreaders shall not exceed 1.0 cfs. The minimum level spreader length used will be 10'. g11 Macl<enan Drive; Cary, NC 275si ; tel:9z9•4�9•3340 ; fax:9i9.238.zo99 ;www.withersravenel.corn i4io Common4ve�(th Drive � Suite aog ; Wilmingtar�, NC z84o3; tel:9io.z56.9z77� fax:9io.z56.z584 q16 D Gal(fmore L7airy Road � Greensboro, NC 27t�og tel: 33�-993-55Q4 BMP# 7 —Wet Pond_Formerly BMP_�_&_7B) -- - Drainage Area =7.73-ac - 2'Wide Weir @ 352.00' - Impervious Area =3.41-ac - t�'x 4' I.D. Riser Box, Crest @ 353�So' - Normai Pool Elev. =3So.5o' - 24" RCP Outlet Inv. =3r�8.00' (2" Diameter Drawdown Orifice) - 4a' Emergency Spillway @ 354•25' BMP_#_8_-Wet Pond (Formerly_BMPZA� - Drainage Area =7.46-ac - 2 — 6" x 4' Orifices @ 3�3•50' - Impervious Area =3.21-ac - 4'x t�' I.Q. Riser, Crest @ 365.00' - Normal Pool Elev. = 361.75' - 36" RCP Outlet Inv. =358.00' (2" diameter Drawdown Orifice) - 4a' Emergency Spillway @ 365�35' BMP#10-_Wet Pand Farmerl BMP C --- -— ---— - Drainage Area =7.8o-ac - 2 — 6"x 3' Orifices @ 373•75 ' - Impervious Area = 2.68-ac - 6'x b' I.D. Riser, Crest @ 376.00' - Normal Pool Elev. =372.00' - 36" RCP Outlet (nv. =368.00' {2" Diameter Drawdawn OriFice) - 40' Emergency Spillway @ 37�•25' BMP#11—Wet Pand (Formeriy BMP io) - Drainage Area = 6.r�o-ac - 6'x 6' 1.D. Riser, Crest @ 3�4•�5' - Impervious Area = 2.39-ac - 36" RCP Outlet Inv. =379•�0' - Normal Pool E1ev. =382.75' - 3a' Emergency Spillway @ 385•00' (2" Diameter Qrawdawn Orifice) BMP Outflow Summ� CH Sells W&R Post- percent �H Se(ls W&R Past- , p�rcent Report Developed Report Developed ' Additional BMP z-yr z-yr Increase ' lg-yr io-yr ' Increase ' petention ' ' Discharge ' Discharge , �Decrease) , a�s�harge ' Discharge tpecrease) ' Required? ' cfs cfs % cfs cfs °!o 7 21.94 7.48 �6�) �5•So �9•45 �17) N 8 �9.29 15•99 ��7) 32,59 28.06 �14) N a.o 16,73 15.11 (so} 30.14 �5.i5 (17) N ii 1y..62 2�.77 76 2y.o4 r�?.27 76 N* *Note: Detention Requirements Met afbownstream Analysis Point BMP Outflaw Summa, �i- ear Starm ' CH Sells W&R Post- p�rcent Repart DeveCoped ' �ncrease Detention ' BMP 1-yr i-yr Discharge Discharge ' {a��rease) Required? cfs cfs °!o 7 16.43 4•30 �74) N . 8 �5.27 11.92 (z2) N 1� 1�#•�� 12.27 (2�� i zz.16 20.46 83 N* *Note: detention Requirements Met at Downstream Analysis Point iiz M�cE�enan Drive= Cary, NC a751s ; te1.919•469•3340 ; fax:gl9.z38.zo9g :, �vww.with�rsrav�n�l.com i410 Common�ve�lth Drive � Suite io1 ; Wilmington, NC z8r�o3 ; te�. ggo.z56.9z�7 fax:9zo.25�.z53y yi6 D Ga�limore Dairy Road � Greensboro, NC 27r�ag tel,;36-9g,-55ot� Entire Phase Outflaw Summa CH Sells ' W&R Post- Percent ' CH Sells W&R Post- ' p�rcent Report Developed Report Developed Additional 2-yr 2_yr Increase 1a_Yr lo-yr Increase Detention ' Discharge ' Discharge �Decrease) ' pischarge Discharge , {Decrease) ' Required? , cfs cfs °la cfs cfs % ' 72.58 59.80 (18) 122.z7 116.i9 �5) � Withers & Ravenel also completed design calculatians for the emergency spilfways per ', the guidance in the current Durham Reference Guide for Development. Far this condition, fihe primary spillway was assumed ta be clogged, resulting in no flow through the primary outlet barrel. For this rauting, the starting water surface in the pond was set to ' the top of the principal spillway. A summary of the starting water surface elevations and resultirtg peak water surface elevations is shown belaw. BMP Design Infa Emergency 5pillway Design Info ' P�n� Riser zo-yr Starting Spi(lway Spillway 25_yr WSEL ' loo-yr E(evation ' WSEL WSEL ' Elev Width WSEL �ft) ' ��) �ft) , (ft) (ft) ({t) (ft) 7 353�50 354.0�. 353•5� '' 354.25 ' 4a 354•79 354•�9 ' 8 365.oa 365.30 365.oa 3b5•35 ', 40 365•89 365�99 io 376.oa 374•74 374.60 ' 376.25 40 376.79 376.89 iz 384.25 3�4•95 384.25 385.oa 3a 385.6b 385.78 Dam Design Top of Design Net Pond . Class Freeboard Settlement Neight Storm 'Dam Elev WSEL Freeboard (ft) ' (ft) �ft) �ft) (ft} tft) 7 6 B 1oo-Y� ' 356•4� 354�89 1.31 0.3o s.o1 8 7.5 B Zoo-yr 367•c�a 365•9g 1•41 0.38 s.a� ia 4.5 C soo-Yr : 37$•5a 376.89 1.6z o.23, i.38 ii 8 B Zoo-yr ' 387,5a 385,78 1,72 0.40 1.32 iiz MacKer�an Drive- Cary, NC i75zs ; teL•g79•4�9�3340 ; fax:gzg.z3�.2o99 i wwGV.withersraveneLcam 1y�o Commonuve�lth Qrive ; Suite sa1 ; Wilmington, IVC zS�o3 ; tel.g�.o.z56.9z77 Fax:g�t7.z56.z584 t;16 D Gallimore Dairy Roa�J � Greensboro, NC 2740� tel:33�-993-55a4