The Basics of Polk County s Impervious Surface Regulations

Transcription

1 The Basics f Plk Cunty s Impervius Surface Regulatins Plk Cunty Land Infrmatin Department Plk Cunty Gvernment Center 100 Plk Cunty Plaza, Suite 130 Balsam Lake, WI Fax

2 Why d we have impervius surface limits? Impervius surfaces dn t allw water t sak int the grund, thereby increasing runff that carries fertilizers, pesticides, and ther pllutants int the lakes and streams. Studies fund that fish ppulatins decline dramatically when mre f the watershed is cvered with hard surfaces such as rftps, rads and driveways. Sme studies have als shwn impervius surfaces harm fisheries because: Warm runff frm rads and ther hard surfaces raises water temperatures and decreases xygen levels, eliminating sme fish species Sediment carried in the runff creates cludy water Sediment cvers spawning areas and clgs the gills f sme fish Ecnmic Studies have shwed a relatinship between water quality and prperty evaluatins. Typically, prperty values are higher n cleaner lakes with better water quality. Impervius surfaces are ften cuntered with balancing mitigatin measures that are designed, implemented, and functin t restre natural functins and values that are therwise lst thrugh develpment and human activities. What is cnsidered impervius surface? Rfs Driveways (gravel & paved) Sidewalks Patis Hw much impervius surface am I allwed n my prperty? The impervius surface standards are frm Wiscnsin Administrative Cde NR Under NR. 115, all impervius surfaces within 300 feet f the rdinary high water mark are calculated. Every prperty is allwed up t 15% f impervius surface withut any mitigatin. Hwever, yu are allwed frm 15-30% f impervius surface, as lng as yu cmplete mitigatin t reduce the runff t the 15% threshld. Prperties with 30% r mre f impervius surface are allwed t maintain and keep their impervius surfaces, but are prhibited frm adding additinal impervius surfaces. Hw d I calculate hw much impervius surface I have? Step 1: Measure r calculate the ttal lt size within 300 feet f the rdinary high water mark. If yur prperty has been surveyed, the dimensins are als n yur survey map alng with the ttal lt size. If yu are measuring a rectangular lt, use the fllwing frmula:

3 Lt width X Lt Depth (within 300 )= Lt Size ft 2 (see Figure 1 belw) If yur lt is irregular in shape, the Plk Cunty GIS map may be the easiest way t calculate the lt size within 300 feet. Use the fllwing link t get t the website: Once n the website, select the Dept Maps tab and zm int yur prperty. Using the Measure Area tl in the Dept Maps tlbar, measure the size f yur lt within 300 f the water. Step 2: Calculate and add up all impervius surfaces within this area n yur prperty. (see Figure 1 belw) Figure 1: Calculating lt size and impervius surfaces Wds Wds Asphalt driveway (690 ft 2 ) Garage 625 ft 2 (25 x25 ) Land use ttals Lt Size 100x200= 20,000 ft ft. Huse 1600 ft 2 (40 x40 ) Sidewalk (125 ft 2 ) Impervius surface Huse: 1,600 ft 2 Additin: 160 ft 2 Garage: 625 ft 2 Driveway: 690 ft 2 Sidewalk: 125 ft 2 3,200 ft 2 Open Space Shrub/ Grass/ Sedge Grass Shrub/ Grass/ Sedge Prpsed 10 x16 sunrm additin (160 ft 2 ) 100 ft. Lake

4 Step 3: Cnvert the amunt f impervius surface int percentage f impervius surface. Using the example abve, yu wuld use the fllwing frmula: Impervius surface (ft 2 )/ Lt size (ft 2 )x100= Percent f impervius 3200/20,000=.16x100=16% Impervius surface S in rder t add the prpsed sunrm, mitigatin is required because yur prperty exceeds 15% impervius surface. Hwever, if yu cmplete this prcess and find yu under 15% f impervius surface, mitigatin wuld nt be required. What are my ptins fr mitigatin? Install and/r maintain a full shreland buffer with allwed viewing crridr Remval r replacement f nncnfrming structures and/r ther impervius surfaces f equal r greater square ftage Nn-cnfrming structures get an additinal bnus f 1.25 square feet per 1 square ft remved. Example: A prperty wner needs t remve 500 sq. ft. f impervius surface in rder t add a 500 sq. ft. additin t their huse. If the impervius surface that the prperty wner wanted t remve was a nncnfrming structure, then they wuld nly need 400 sq. ft. t qualify. Land Use Runff Rating Calculatin: The prperty wner can utilize the Land Use Runff Rating as a mitigatin calculatr t determine the amunt f mitigatin required. The prpsed develpment (after prpsed imprvements) runff rating shall be based n the land cver, existing impervius surfaces, and sil types. The prpsed impervius surface runff amunt must be less than r equal t the amunt f runff generated frm 15% f impervius surface n the lt. Optins t equalize these values may include, but are nt limited t: Vegetative Plantings, Rain gardens, Impundments, including but nt limited t, infiltratin pits and rainwater harvesting. Hw t calculate the Land Use Runff Rating? A runff rating number is determined fr the entire lt within 300 feet f the rdinary high water mark. T calculate the runff rating the landwner/agent must cmplete the fllwing steps: Measure each land use n the lt and draw them t dimensin r scale. Calculate the ttal square ftage f impervius surface and land surface type n the prperty. Determine the Hydrlgic Sil Type (HST) frm the GIS map (Plk Cunty, WI» WG Xtreme) r cntact the Zning Department. T find the Hydrlgic Sil Type, select the Dept Maps tab n the GIS map Then select Zning frm the drp dwn list in the tlbar Apply the Sils Hydr layer t yur prperty and use the key t check the sil type. (Yur screen shuld lk similar t the ne belw)

5 Using the runff rating wrksheet, enter the square ftage fr each land cver type in the respective clumns based n the sil type. The Ttal Area must meet the ttal lt size within 300 f the water. The prpsed impervius surface clumns will be autmatically filled with the values entered frm the 15% impervius surface clumns fr cnvenience. User input is required t change these quantities t their apprpriate values. Pint Credits: A ne pint credit will be applied fr the lts with public sewage and a 1.5 pint credit fr landwners wh establish cntinuus vegetative cver starting frm the OHWM and cntinuing landward 35 feet. (Allwed Viewing Crridr) Other practices r measures that the cunty determines adequate t ffset the impacts f impervius surface n water quality, near shre aquatic habitat, upland wildlife habitat and natural and scenic beauty. (i.e. practices fund in Wiscnsin Field Office Technical Guide r NRCS Technical Standards) T apply a pint credit, subtract the number f pints yu qualify fr frm the Prpsed LURR. The wrksheet will calculate if mitigatin is required, and hw much mitigatin is needed fr each mitigatin ptin.

6 Any cmbinatin f the fur mitigatin ptins is allwed, but yu nly have t pick ne ptin. If yu are ding half raingardens and half native plantings, we wuld take the ttal area required fr each ptin and multiply them by 50% t equal a ttal f 100%. (Prrated) Additinal mitigatin requirements: Mitigatin plans, including existing mitigatin ptins, must be recrded by an affidavit in the Register f Deeds. Mitigatin plans will have tw calendar years t be installed. If mitigatin ptins are nt installed and established within tw years f issuance f a permit, then citatins shall be issued and a new permit culd be required. Fr each mitigatin plan, dated pht dcumentatin f the mitigatin area during and/r after the mitigatin installatin, as apprpriate t shw cmpliance, must be submitted as part f the applicatin. Mitigatin must be maintained and is subject t peridic cmpliance checks.