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Home My WebLink About1997-04-17 Work Session MINUTES OF DRAINAGE WORK SESSION, APRIL 17, 1997 PAGE 930 ASSEMBLY The New Hanover County Board of Commissioners held a Work Session on Thursday, April 17, 1997, at 10:30 A.M. in Room 50 I of the New Hanover County Administration Building, 320 Chestnut Street, Wilmington, North Carolina. e Members present were: Commissioners Ted Davis, Jr; Charlie R. Howell, Vice-Chairman William A. Caster; Chairman Robert G. Greer; County Manager, Allen O'Neal; County Attorney, Wanda M. Copley; and Clerk to the Board, Lucie F Harrell. Chairman Greer called the Work Session to order and stated the purpose of the meeting was to discuss proposed drainage regulations. He requested the Assistant County Manager, Dave Weaver, to begin the presentation. PRESENTATION OF INTERIM DRAINAGE REGULATIONS Assistant County Manager Weaver reported on January 6, 1997, the Planning Board * ' . - . submitted recommended drainage regulations to the Board of County CClmmissioners. At the meeting, the Commissioners felt the issue was quite complex and de,cjded that more time was needed to review the regulations. During the retreat held on January 17-18, 1997, the Board held a Work Session on drainage, and as a result the Homebuilders Association formed a Drainage'Committee and invited County Staff to participate and formulate interim drainage regulations. Overall the Committee fur]ctioned well with only a few disagreements on certain regulations; however, the proposed regulations will serve as a starting point until the Pages Creek Watershed Study has been completed and sufficient information is available to determine the best approach for developing a county-wide drainage plan. e The following interim drainage regulations prepared by the Homebuilders Association Drainage Committre were presented for, residential development: (I) The maximum rate of discharge for any storm up to a 2 or 1:0 year storm after development shall not exceed the maximum rate of discharge for, respectively, 2 and 10 year storms for the site before developmen,t. This requireIJ1ent will not apply to subdivisions wh,ere all lots are greater than 20;000 square feet. ' The following definitions were presented: . . . " ,.' , ; (, '~"; ;, I,ll. Discha:r~e Rate: The discharge rate is measured in cubic feet per second at the point where the drainage way leaves the parcel that is being developed. .. ,', I., .. , ~i Two-year Stoim: A 2 year storin is a storin that has \1'50% chance of occurring in any 'given year. A' 2 'year storm occurring over a period'.of 24 hours would produce , approximately,~ 7? inches of rainfall., " . ", ., ""J ~ I' \ '1,'. I, l'~",,' ,. " j."", t." do::' 'I':.;.": l~.~ I. 'Ten Yelll' Storm:':A:."1 0 year' storm is ~ storn! iii.i'Fh~s': ,nD% chanc~ of occurring in any given year. A 10 year storm occurring over a period of24 hours would produce approximately' 7 inches ofrainfall. " ""', ,,;. . e The post-developIpent rate of discharge cannot e,xceed the pre-development of discharge.' ..' 1- '. ." .'> . 4' ).. ., " .-: .lf~, !. . " Assistarit CoUntY Man:~g'er Weaver 'advised the reguliiiions' would apply only to'conventional R-20 resid!lntjal s.iibdivisio~s, '~ot pei%imance residential subdivi~ions because,there will be lots I~ss than 20,090 ~quare(eet. Staff,feels this is a,w~akness in the drainage r!lg~l~tion because the m~er in which drajmig'e is han,qle4 from t4e ~Cla:d system in all ~u\Xliv\s\ons det~~ines,the ~.Olp~t pf the discharge rate, not the number o~ lots, I' ..; ;, l,.'" , .' f. " .1:, ,I ..:.l~'_ i~:, ~,,;[ . .,:' I I:. Commissioner Davis aSked if the County shouldretn6ve"'th!l;exemptiori from the drainage regulation? >, , . , .. '"<',., , I. >, .\ c., I"". ,. ,. ",f ,. ';'. "; MINUTES OF DRAINAGE WORK SES~ION, APRIL 17, 1997 PAGE 931 . Assistant County Manager Weaver advised the regulations should apply to all subdivisions whether conventional or performance residential. He advised that under R-20S zoning, the subdivision lots are 20,000 plus square feet; therefore, the standard would not apply When. developing large lots with no curb and glitter, the developer will easily meet the discharge rate with no other improvements. Discussion was held on the difference between R-20 conventional residential development and R-20 performance residential development. Under R-20 conventional residential, all lots must be greater than 20,000 square feet. Under R-20 performance residential, the number of acres that can be developed are multiplied by 1.9 units per acre; therefore, if a developer has 10 acres, there would be 19 buildable lots. o Chairman Greer stated if the buildable acreage remains the same, there should be no difference in the discharge rate. Planning Director, Dexter Hayes, stated if lots were clustered in one area on a large tract of land under performance residential standards, the amount of water coming from this area could be intense and would have to be well managed to control the discharge rate. Assistant County Manager Weaver presented the following definition before presenting the detention regulations: (1) detention means the storm water is held on site for a short period time, two to five days; and (2) retention means the storm water is held on the site permanently until it percolates into the soil or evaporates. (2) All residential development must detain storm water runoff from impervious surfaces for a draw-down period of two to five days at the following rates: (i) 0 to 1.9/units/acre No detention required (R-20 & R-20 Performance Resid.) o (ii) Subdivisions where all lots are Greater than 15,000 sq. ft. (Conventional R-15) No detention required (iii) R-15 performance residential (2.5 units/acre) I" detention required (iv) Greater than 2.5 units/acre (High density; R-IO) 1.5" detention required A chart was presented showing. the discharge rate under natural conditions in comparison to a developed site. If property is developed with no drainage controls, there will be a higher discharge rate and volume of water. Ifa site is developed with discharge rate controls, the rate will not exceed the discharge rate under pre-developed conditions. Discussion was held on whether the rate of volume should be controlled. Assistant County Manager Weaver advised developing regulations to control the rate of volume were more complicated and should not be considered until after completion of the Pages Creek Watershed Study o (3) . Discharge of runoff from impervious surfaces directly into natural water bodies shall be avoided where practical. Runoff should be routed through vegetative swales, detention areas or other filter media for purposes of increasing percolation, settling lind filtering of on-point pollutants, and decreasing discharge velocity Commissioner Davis referenced the second sentence and asked if the word, shall, should be used after runoff instead of should? JI..N.""",,",, tH "" .J:4~~.,. ;1(4~~' MINUTES OF DRAINAGE WORK SESSION, APRIL 17, 1997 PAGE 932 Assistant County Manager Weaver advised this language was used to accommodate certain lots. For example, steep, sloping lots could not utilize swales. He recommended allowing the language to remain unchanged. (4) The use of wetlands, natural depressions, and areas of good draip.ing soil is strongly encouraged in the development of drainage plans. . e (5) County Ordinance regulations will remain in effect. ..l.' ~ .' , The Homebuilders Association Drainage Committee recommended consideration of. the following items: . ,I: (I) The Board of County Commissioners should initiate a maintenance drainage program for FY 1997-98. (2) The Board should adopt the following regulations: (i) All lot owners shall be responsible for maintenance of swales, ditches, and other drainage ways included as part of an approved subdivision that are located on their lot. ", ., j! (ii) No one shal1"be allowed to fill, pipe, place materials (rubble, leaves, etc.) in, or otherwise alter swales, ditches, or other drainage ways without prior approval of the County. (iii) The County has the right to perform drainage work and to charge property owners -for the work, if the above violations occur. e Assistant Coiinty Manager Weaver reported the County''Attomey had drafted an ordinance to include the above regula~ions in the New Hanover County Code. e Discu~sio~ y.'as held on existing drainage regulations 'Versus the prop.osed regulations. County Engineer, v.;yatt Blanchard, reported under existing regulations, the drainage in subdivisions was collected in the roads and'released into short vegetated swales gradually emptying into a large ditch as required by the State"ofNorth Carolina. State regulations protect the water quality but do not control the discharge rate. U:p.der the propose~ drainage regula~ions, the County Engineer determines if detention panas aie'required'accordiiig'to' tJ{e'~ize"(jf'tI1:e tract: This approach divides the subdivisions into"snlall watersheds' to control the discharge r~te.:'Thetcost f6r requiring detention pop.ds will cost approxi~at.e'y $2,000 per lot. Discussion was held on h!J\v'the figUres and- statisticS"weie' developed for the amount ot rainfall. Sheets were presented shoWing how the State dilcullltes'the fomniia:' Further discussi~n was held on the amount of rainfall produced by a heavy thunde~storm. Engi~eer, Jim Craig, reported the amount of rainfall during a heavy thunder storm could be from two to four inches. , \ ,i .,.: I~ ':; _ ,I .' 11 :. , ..., '\., A lengthy discussion washeld'oii the benefits Of the interim drainage regulations, ,Assistant County Manager Weaver advised that Staff felt the proposed regulations should be strengthened; however, the propo~'edreg~iatio'hs ;Will~erlr~ 'iis il'Sfuqihg p6intJAtil"the'i>'ag~s Creek Wa:te~shed 'r _ ....\ ", . ,Ie.., .' ; " ~ ,'). Study has been completed. 'He emphasized the importance of everyone understanding that the propose drainage regulations, will not resolve the County's dr~inage problems, I"~ ~ OJ'.~, '<;' ~I;~: i.!J, ','\1 l't '. '(".~ I ,'q.~. '.,,,.' '..;.\' 'I.' rl. 'I'" ChaiI:ffian,Gre~r' expr~'ssed 'appUcilition to Staff for 'an in(drma!ive. pre'sehtation, 'and stated a Public Heirring 'ha~' been 'scheduled for April ,28; 1997, to receive' public '~o;nments about the proposed'regulati6ns," d' " ".!..' ,:' ..,:. ' " .,' .1' ..~. '~"d' ;. ~_ ..: ,.l' ,. e,/.." ( ~;'I,~":I""a~ :; :"_ '1 ""._ .. :-.; ,i< if ~,~' :"1 I ~ ~af ,,- ... ,. ,.. , I.,. ,I',:, 1'" ,~, ~ '~", '1;',\ '. .." ~ ,:.~ ". '..... ,,-:: t, " ~ ..' -. . ""1 '" r. t\ ..,.~\ :~, .);i"'~ "~:" ''i~..~t~,~; ';,'/ J' ':' - -",!, ~ ,'.i. ~, ~ .11 it, \ ,~~, ~ .. :'l ~\ ~' ~ "..,'1(' ..~ ~ _1 .~, 1', _, p. \l..t,;,: i. '" ~ .:.~ ,~J _'1~~~ !,,\..' r1,\( t.,'~""... ~ t;,: . " .. , , \, :~~~f"f~,YH l,,.i .;:~:Ju~,.,t:l i:'\~ .p~'\ j '~'.\ ;, _J ,I ./1, I ;';r,:,!)-'~,'r.' .1 It .~,ji i,'.l;'l;:\' :;, 1,.)'-' "\...-:, " I.."'. ~ ~J.~: il ':, 1: '-',.1 c ' MINUTES OF DRAINAGE WORK SESSION, APRIL 17, 1997 ADJOURNMENT Chairman Greer adjourned the Work Session at 12:30 P.M. PAGE 933; Respectfully submitted, ~~~ Clerk to the Board I II , I J , , ~ o o o