STORMWATER MANAGEMENT COMPUTATIONS. Mount Prospect

Transcription

1 STORMWATER MANAGEMENT COMPUTATIONS Mount Prospect MHG PROJECT No November 6, 2014 Prepared for: Piney Meetinghouse Investments c/o Mr. Dennis Fling Clopper Road Boyds, MD (301)

2 Project: Mount Prospect MHG Proj. No.: Date: November 5, 2014 Background Drainage ESD MEP STORMWATER MANAGEMENT SUMMARY OVERALL SITE DESCRIPTION The 9.47 acre property is located at 230 McCrossin Lane in Potomac, Maryland. The existing property consists of existing Parcel P570, Liber 4461, Folio 256, and is proposed to be subdivided into 3 buildable lots: Lot 1, Lot 2, and Lot 3. The property is currently zone RE-2. The existing on-site buildings will be demolished and 3 single family homes will be constructed, 1 on each lot. These homes will be serviced by a single shared driveway. This property will go through the Preliminary Plan of Subdivision Process. This site drains to the Potomac Direct tributary. This portion of the Watts Branch Watershed is designated as class I-P waters by the State of Maryland. Under existing conditions, runoff from Lots 1, 2, and part of Lot 3 generally flows southeast through the site and adjoins with the southernmost point of Lot 3 at Sandy Branch stream, which flows southwest and continues offsite. With the proposed development, the direction of flow continues to run towards the southeast portion of the site, but is largely contained within the vicinity of the proposed stormwater management facilities. The proposed conditions will also slightly lower the flow rate into the site under both 10 and 100-year circumstances. A floodplain is shown on-site per FEMA Map Number 24031C0310D. This property does not exist within a Special Protection Area. Stormwater Management Stormwater management for the proposed site is designed such that environmental site design (ESD) techniques have been proposed to treat the entire volume of runoff generated by the property under proposed conditions. Each lot will contain three gravel dry wells, which will be situated around each house to treat the runoff from the roof drains. In Lots 1 and 2, grass swales are proposed to treat runoff from their corresponding driveways. Any additional runoff on lots 2 and 3 will be directed towards a micro-biorentention area located on either site. Limitations A major limitation to achieving ideal stormwater management design is the existing soil. Part of Lot 2 and the majority of Lot 3 is dominated by soil belonging to hydrologic group D, which has properties such as a potentially high water table, clay near the surface layers of soil, slow infiltration rates and, in effect, a high runoff potential. In addition, the majority of Lot 3 consists of steep slopes, which disallow several types of ESD practices. Soil testing is pending to determine the extent of these limitations.

3 Summary of ESD Practices Green Roof: Green roof technology was not proposed because alternate ESD practices are proposed to manage the roof area. Pervious Pavement: Pervious pavement was not explored because other lower maintenance ESD practices are proposed and can manage the entire ESDv requirement. Reinforced Turf: Reinforced turf was not explored because all surface paving is expected to be too heavily used to be practical. Disconnection of Rooftop Runoff: This practice is not feasible for this site due to steep slopes; alternate ESD practices are proposed to fulfill the ESDv requirement. Disconnection of Non-Rooftop Runoff: This practice is not feasible for this site due to steep slopes; alternate ESD practices are proposed to fulfill the ESDv requirement. Sheetflow to a Conservation Area: Conservation areas are not located in areas that are conducive to receiving sheetflow from the proposed development area. Rainwater Harvesting: Rainwater harvesting was not explored because year-round demand cannot be practically provided. Submerged Gravel Wetland: Submerged Gravel Wetlands are not suggested because it is not aesthetically appropriate for the proposed houses. Landscape Infiltration: Landscape infiltration is not currently proposed because soils analysis is still pending. Infiltration Berms: Infiltration Berms are not proposed because full ESDv management can be provided using other ESD practices that are more reliably constructible. Dry Wells: Dry wells are proposed to treat the majority of the new rooftop area. Micro-Bioretention: Micro-bioretention is proposed to treat portions of the proposed paved areas. Rain Garden: Rain gardens were not proposed because alternate and more efficient ESD measures are proposed in the open space areas. Swales: Grass swales are proposed to manage a portion of the paved area.

4 SWM COMPUTATIONS Mount Prospect MHG PROJECT No Table of Contents: Lot 1 ESD Sizing Criteria 1-3 ESD Micro-Scale Treatment Summary 4 Average Treatment P E Calculation 5 ESD Micro-Scale Reduced RCN Calculation 6 Dry Well Design: DW-1A 7 Dry Well Design: DW-1B 8 Dry Well Design: DW-1C 9 Grass Swale Design: GS Lot 2 ESD Sizing Criteria ESD Micro-Scale Treatment Summary 16 Average Treatment P E Calculation 17 ESD Micro-Scale Reduced RCN Calculation 18 Dry Well Design: DW-2A 19 Dry Well Design: DW-2B 20 Dry Well Design: DW-2C 21 Micro-Bioretention Design: MB Grass Swale Design: GS-2A Grass Swale Design: GS-2B Lot 3 ESD Sizing Criteria ESD Micro-Scale Treatment Summary 34 Average Treatment P E Calculation 35 ESD Micro-Scale Reduced RCN Calculation 36 Dry Well Design: DW-3A 37 Dry Well Design: DW-3B 38 Dry Well Design: DW-3C 39 Micro-Bioretention Design: MB

5 DATE: 11/6/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 1 Site Data: Total Drainage Area (DA): 101,000 SF = 2.32 Acres Total Impervious (I) Area: 6,550 SF = 0.15 Acres = 6.5% Determine Target P E : Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) % of Total DA 0.0% 101,000 SF 100.0% 0.0% HSG I Area (SF) HSG %I 0.0% 6,550 SF 6.5% 0.0% 0.0% HSG RCN HSG P E * 0.0'' 1.0'' 0.0'' 0.0'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Target RCN = 55 x 100% = 55.0 Target Rainfall = P E = 1'' x 100% = 1.00'' LOT 1 Environmental Site Design (ESD) Sizing Criteria HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.0'' 1.2'' 5% % % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.0'' 1.2'' % %

6 Proposed Disturbed Area: PAGE: 2 Total Disturbed Area (LOD): 38,000 SF = 0.87 Acres Impervious Area (I) Within LOD: 5,686 SF = 0.13 Acres = 14.96% Determine Q E : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (14.96%) = 0.18 Q E = Runoff depth in inches that must be treated using ESD practices = P E x R V = 1'' x 0.18 = 0.18'' Determine ESD V : ESD V = Runoff volume used in the design of specific ESD practices (P E )(R V )(A) = where A is the drainage area (in square feet) (1'')(0.18)(38000) = = 585 CU FT

7 Minimum ESD Target: PAGE: 3 As a minimum, ESD shall be used to address both Re v and WQ v requirements Determine RE V : Re V = Groundwater Recharge volume component of ESD V (S)(R V )(A) = (0.26'')(0.18)(38000) = = 152 CU FT SOIL SPECIFIC RECHARGE FACTOR (S) HSG (S) % AREA (S)(%A) A % 0 B % 0.26 C % 0 D % 0 COMPOSITE S = 0.26 Determine WQ V : Wq V = Water Quality volume component of ESD V = 1.0" Eastern Zone and 0.9" Western Zone (P E )(R V )(A) = where A is the drainage area (in square feet) (1'')(0.18)(38000) = = 585 CU FT

8 JOB #: DATE: 11/6/2014 Macris, Hendricks & Glascock, P.A. PAGE: Wightman Road, Suite 0 ESD SUMMARY - LOT 1 TREATMENT IMPERVIOUS UNIT NO. FACILITY DESCRIPTION AREA (SF) AREA (SF) P E (IN) R V ESD V DW-1A Dry Well DW-1B Dry Well DW-1C Dry Well GS-1 Grass Swale 1,960 1, TOTALS 4, , AVG. PE 1.88 R V = (I) (P E )(R V )(A) (ESD V ) ESD V = PE = where I is percent impervious cove (RV)(A)

9 DATE: 11/6/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 5 It is not practicable for all parts of the development area to drain to stormwater facilities. It is therefore necessary to average the treated ESDv from all drainage areas over the entire development area. This is accomplised using the relationship between P E and ESDv such that the ESDv term is the summation of all treated stormwater volumes, while the site data is based on the development area. Determine Avg. Treatment P E for Total Site: P E = (ESD V ) (RV)(A) Treated ESDv = 649 CU FT Disturbed Area (LOD) = 38,000 SF Rv = 0.18 Avg. P E = (649) (0.18)(38000) Avg. Treatment P E = 1.11 Average Treatment P E for Development Area (From ESD SUMMARY Sheet) Target P E = Avg. Treatment P E = ESDv Required = ESDv Provided = 1.00'' 1.11'' 585 cu ft 649 cu ft

10 DATE: 11/6/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE 6 Design Treatment P E= 1.11'' Use 1.0'' Site Data: LOT 1 Environmental Site Design (ESD) Sizing Criteria Total Drainage Area (DA): 101,000 SF = 2.32 Acres Total Impervious (I) Area: 6,550 SF = 0.15 Acres = 6.5% Determine Reduced RCN: Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) 0 SF 101,000 SF 0 SF 0 SF % of Total DA 0.0% 100.0% 0.0% 0.0% Site %I 6.5% 6.5% 6.5% 6.5% HSG RCN* Design P E 0.0'' 1.0'' 0.0'' 0.0'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Design RCN = 55 x 100% = 55.0 Design RCN (55) < or = Target RCN (55) THUS REDUCED RCN = ''WOODS IN GOOD CONDITION'' AND CPv HAS BEEN SATISFIED HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.0'' 1.2'' 5% % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.0'' 1.2'' 5% % % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.0'' 1.2'' 5% % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.0'' 1.2'' 5% % %

11 DATE: 10/22/2014 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 7 Design Goals: Target Rainfall = P E = 2.60 Target Runoff = Q E = 2.47 in Target Runoff = ESD V = 494 ft 3 in 75% ESD V = ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.6 in ESD V = 165 ft 3 LOT 1 - DW-1A Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

12 DATE: 10/22/2014 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 8 Design Goals: Target Rainfall = P E = 2.60 Target Runoff = Q E = 2.47 in Target Runoff = ESD V = 494 ft 3 in 75% ESD V = ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.6 in ESD V = 165 ft 3 LOT 1 - DW-1B Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

13 DATE: 10/22/2014 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 9 Design Goals: Target Rainfall = P E = 2.60 Target Runoff = Q E = 2.47 in Target Runoff = ESD V = 494 ft 3 in 75% ESD V = ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.6 in ESD V = 165 ft 3 LOT 1 - DW-1C Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

14 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 10 Design Goals: Target Rainfall = P E = 1.80 in Target Runoff = Q E = 0.74 in Target Runoff = ESD V = 301 cu ft LOT 1 - GS-1 Grass Swale Design Site Data: Drainage Area (DA) = 4,900 sq ft Impervious Area (I) = 1,960 sq ft Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.41 x 4900) / = 435 cu ft Design Equations: From 2000 Maryland Stormwater Design Manual ESD V = (P E )(R V )(A) Grass Swale Design: Swale Width (W f ) = 3.00' Swale Length (L) = 150' Surface Area (A f ) = 450 sq ft % of DA (2.0% min) = 9.18% Longitudinal Slope (S) = 4.00% (4.0% max) Swale Side Slope (m) = 3 : 1 P E = 1.0'' (P E )(R V )(A IMP ) ESD V = (1)(0.95)(1960) = ESD V = 155 cu ft

15 Determine ESD V Discharge: PAGE: 11 Flow Rate, Q Design Rainfall = 2.6 in Proposed Condition RCN = 75.8 Runoff = 0.75 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/75.8) -2 = Ia/P = (0.639)/2.6 IN = tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 958 CSM/IN OR CFS/AC/IN qi = (0.75 IN)(1.496 CFS/AC/IN)(0.11 Ac.) = 0.13 CFS Flow Depth, d Q = (1.49/n)*A*R 2/3 *S 1/2 A = 1/2*d(2*W f +2*m*d) R = A / P P = W f + 2*d*(1+m 2 ) 1/2 Manning's n = 0.15 For Flow Depth d = FT 4'' Flow Area (A) = 0.50 SF Wetted Perimetter (P) = 3.92 FT Hydraulic Radius (R) = 0.13 FT Flow Rate (Q) = 0.25 CFS Flow Velocity, V V = Q / A Velocity (V) = 0.50 FPS 1 FPS

16 Determine 10-Year Discharge: PAGE: Design Rainfall = 5.1 in Proposed Condition RCN = 75.8 Runoff = 2.60 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/75.8) -2 = Ia/P = (0.639)/5.1 IN = 0.5 tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 1002 CSM/IN OR CFS/AC/IN qi = (2.6 IN)(1.566 CFS/AC/IN)(0.11 Ac.) = 0.5 CFS Flow Depth, d Q = (1.49/n)*A*R 2/3 *S 1/2 A = 1/2*d(2*W f +2*m*d) R = A / P P = W f + 2*d*(1+m 2 ) 1/2 Manning's n = 0.06 Flow Depth d = 0.13 FT Flow Area (A) = 0.4 SF Wetted Perimetter (P) = 3.8 FT Hydraulic Radius (R) = 0. FT Flow Rate (Q) = 0.52 CFS Flow Velocity, V V = Q / A Velocity (V) = 1.18 FPS 4 FPS, non-erosive

17 DATE: 11/7/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 13 Site Data: LOT 2 Environmental Site Design (ESD) Sizing Criteria Total Drainage Area (DA): 90,150 SF = 2.07 Acres Total Impervious (I) Area:,600 SF = 0.29 Acres = 14.0% Determine Target P E : Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) 71,950 SF 18,200 SF % of Total DA 0.0% 79.8% 0.0% 20.2% HSG I Area (SF),600 SF 0 SF HSG %I 0.0% 17.5% 0.0% 0.0% HSG RCN HSG P E * 0.0'' 1.2'' 0.0'' 1.0'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Target RCN = 55 x 79.8% + 77 x 20.2% = 59.4 Target Rainfall = P E = 1.2'' x 79.8% + 1'' x 20.2% = 1.16'' HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.0'' 1.2'' 1.4'' 15% % % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.0'' 1.2'' % %

18 Proposed Disturbed Area: PAGE: 14 Total Disturbed Area (LOD): 65,800 SF = 1.51 Acres Impervious Area (I) Within LOD:,450 SF = 0.29 Acres = 18.92% Determine Q E : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (18.92%) = 0.22 Q E = Runoff depth in inches that must be treated using ESD practices = P E x R V = 1.16'' x 0.22 = 0.26'' Determine ESD V : ESD V = Runoff volume used in the design of specific ESD practices (P E )(R V )(A) = where A is the drainage area (in square feet) (1.16'')(0.22)(65800) = = 1,401 CU FT

19 Minimum ESD Target: PAGE: 15 As a minimum, ESD shall be used to address both Re v and WQ v requirements Determine RE V : Re V = Groundwater Recharge volume component of ESD V (S)(R V )(A) = (0.22'')(0.22)(65800) = = 265 CU FT SOIL SPECIFIC RECHARGE FACTOR (S) HSG (S) % AREA (S)(%A) A % 0 B % C % 0 D % 0.01 COMPOSITE S = Determine WQ V : Wq V = Water Quality volume component of ESD V = 1.0" Eastern Zone and 0.9" Western Zone (P E )(R V )(A) = where A is the drainage area (in square feet) (1'')(0.22)(65800) = = 1,208 CU FT

20 JOB #: DATE: 11/7/2014 Macris, Hendricks & Glascock, P.A. PAGE: Wightman Road, Suite 0 ESD SUMMARY - LOT 2 TREATMENT IMPERVIOUS UNIT NO. FACILITY DESCRIPTION AREA (SF) AREA (SF) P E (IN) R V ESD V DW-2A Dry Well DW-2B Dry Well DW-2C Dry Well MB-2 Micro-Bioretention 16,000 4, GS-2A Grass Swale 2,750 2, GS-2B Grass Swale 1,450 1, TOTALS 22, , ,534.8 AVG. PE 1.68 R V = (I) (P E )(R V )(A) (ESD V ) ESD V = PE = where I is percent impervious cove (RV)(A)

21 DATE: 11/7/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 17 It is not practicable for all parts of the development area to drain to stormwater facilities. It is therefore necessary to average the treated ESDv from all drainage areas over the entire development area. This is accomplised using the relationship between P E and ESDv such that the ESDv term is the summation of all treated stormwater volumes, while the site data is based on the development area. Determine Avg. Treatment P E for Total Site: P E = (ESD V ) (RV)(A) Treated ESDv = 1,535 CU FT Disturbed Area (LOD) = 65,800 SF Rv = 0.22 Avg. P E = (1534.8) (0.22)(65800) Avg. Treatment P E = 1.27 Average Treatment P E for Development Area (From ESD SUMMARY Sheet) Target P E = Avg. Treatment P E = 1.16'' 1.27'' ESDv Required = 1401 cu ft ESDv Provided = 1535 cu ft

22 DATE: 11/7/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 18 Design Treatment P E= 1.27'' Use 1.2'' Site Data: LOT 2 Environmental Site Design (ESD) Sizing Criteria Total Drainage Area (DA): 90,150 SF = 2.07 Acres Total Impervious (I) Area:,600 SF = 0.29 Acres = 14.0% Determine Reduced RCN: Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) 0 SF 71,950 SF 0 SF 18,200 SF % of Total DA 0.0% 79.8% 0.0% 20.2% Site %I 14.0% 14.0% 14.0% 14.0% HSG RCN* Design P E 0.0'' 1.2'' 0.0'' 1.2'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Design RCN = 55 x 79.8% + 77 x 20.2% = 59.4 Design RCN (59.4) < or = Target RCN (59.4) THUS REDUCED RCN = ''WOODS IN GOOD CONDITION'' AND CPv HAS BEEN SATISFIED HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.0'' 1.2'' 1.4'' 10% % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.0'' 1.2'' 1.4'' 10% % % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.0'' 1.2'' 1.4'' 10% % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.0'' 1.2'' 1.4'' 10% % % 84 77

23 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 19 Design Goals: Target Rainfall = P E = 2.60 Target Runoff = Q E = 2.47 in Target Runoff = ESD V = 494 ft 3 in 75% ESD V = ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.6 in ESD V = 165 ft 3 LOT 2 - DW-2A Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

24 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 20 Design Goals: Target Rainfall = P E = 2.60 Target Runoff = Q E = 2.47 in Target Runoff = ESD V = 494 ft 3 in 75% ESD V = ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.6 in ESD V = 165 ft 3 LOT 2 - DW-2B Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

25 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 21 Design Goals: Target Rainfall = P E = 2.60 Target Runoff = Q E = 2.47 in Target Runoff = ESD V = 494 ft 3 in 75% ESD V = ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.6 in ESD V = 165 ft 3 LOT 2 - DW-2C Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

26 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 22 LOT 2 - MB-2 Micro-Bioretention Design Site Data: Drainage Area (DA) = 16,000 sq ft Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.29 x 16000) / = 1,0 cu ft Upstream ESDv Provided= cu ft Maximum Runoff Volume = 1,0 cu ft Effective Drainage Area: Upstream ESD V Provided = 0 cu ft or 0% of Maximum Runoff Volume Effective Drainage Area = x 100% = sq ft Design Equations: From 2000 Maryland Stormwater Design Manual ESDv = (P E )(R V )(A) P E = (ESDv)() (Rv)(A) Facility Design: A f = 325 sq ft (2 % DA) Bottom Storage Area = 325 sq Elev 0.00' Top Storage Area = 430 sq Elev 0.50' Storage Depth = 0.50' Temp. Ponding Volume = 189 cu ft Planting Media Depth = 3.5 ft (2.0'-4.0') Sand Layer Depth = 0.5 ft Porosity (n) = 0.40 Media Storage Volume = 520 cu ft Total ESDv Provided = 709 cu ft P E = ()(ESDv) (Rv)(A) = ()(709) (0.29)(16000) P E = 1.82 in

27 Enhanced (Y or N): N Enhanced Filter - Stone Reservoir Design: PAGE: 23 S = Re V = 0.26 in 101 cu ft A f = 325 sq ft Depth (D) = 1.0 ft Porosity (n) = 0.4 Vol. of Stone = 325 cu ft Vol. of Storage= 130 cu ft P E in Stone Reservoir = ()(ESDv) (Rv)(A) = ()(130) (0.29)(16000) = 0.33 in Total Facility Treatment Provided: ESDv treated by Filter = 709 cu ft ESDv treated by Enhancement = N/A Total ESDv Treatment = 709 cu ft P E treated by Filter = P E treated by Enhancement = Total P E Treatment = 1.82 in N/A 1.82 in

28 Determine 10-Year Discharge: PAGE: 24 Design Rainfall = 5.1 in Proposed Condition RCN = 70.9 Runoff = 2.19 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/70.9) -2 = Ia/P = (0)/5.1 IN = 0 tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 987 CSM/IN OR CFS/AC/IN qi = (2.19 IN)(1.543 CFS/AC/IN)(0.37 Ac.) = 1.2 CFS Determine 10-Year WSEL: Inlet Weir Crest = 0.50' Inlet Weir Length = 5.0' c = 3.1 Q 10 = 1.2 CFS Q = c * L * H 1.5 H = WSEL 10 = 0.18' 0.68'

29 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 25 Design Goals: Target Rainfall = P E = 1.20 in Target Runoff = Q E = 0.26 in Target Runoff = ESD V = 320 cu ft LOT 2 - GS-2A Grass Swale Design Site Data: Drainage Area (DA) = 14,500 sq ft Impervious Area (I) = 2,750 sq ft Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.22 x 14500) / = 693 cu ft Design Equations: From 2000 Maryland Stormwater Design Manual ESD V = (P E )(R V )(A) Grass Swale Design: Swale Width (W f ) = 2.00' Swale Length (L) = 118' Surface Area (A f ) = 236 sq ft % of DA (2.0% min) = 1.63% Longitudinal Slope (S) = 4.00% (4.0% max) Swale Side Slope (m) = 3 : 1 P E = 1.0'' (P E )(R V )(A IMP ) ESD V = (1)(0.95)(2750) = ESD V = 218 cu ft

30 Determine ESD V Discharge: PAGE: 26 Flow Rate, Q Design Rainfall = 2.6 in Proposed Condition RCN = 68.0 Runoff = 0.43 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/68) -2 = 0.94 Ia/P = (0.94)/2.6 IN = tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 868 CSM/IN OR CFS/AC/IN qi = (0.43 IN)(1.357 CFS/AC/IN)(0.33 Ac.) = 0.2 CFS Flow Depth, d Q = (1.49/n)*A*R 2/3 *S 1/2 A = 1/2*d(2*W f +2*m*d) R = A / P P = W f + 2*d*(1+m 2 ) 1/2 Manning's n = 0.15 For Flow Depth d = FT 4'' Flow Area (A) = 0.39 SF Wetted Perimetter (P) = 3.00 FT Hydraulic Radius (R) = 0.13 FT Flow Rate (Q) = 0.20 CFS Flow Velocity, V V = Q / A Velocity (V) = 0.51 FPS 1 FPS

31 Determine 10-Year Discharge: PAGE: 27 Design Rainfall = 5.1 in Proposed Condition RCN = 68.0 Runoff = 1.95 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/68) -2 = 0.94 Ia/P = (0.94)/5.1 IN = tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 980 CSM/IN OR CFS/AC/IN qi = (1.95 IN)(1.531 CFS/AC/IN)(0.33 Ac.) = 1 CFS Flow Depth, d Q = (1.49/n)*A*R 2/3 *S 1/2 A = 1/2*d(2*W f +2*m*d) R = A / P P = W f + 2*d*(1+m 2 ) 1/2 Manning's n = 0.06 Flow Depth d = 0.23 FT Flow Area (A) = 0.6 SF Wetted Perimetter (P) = 3.5 FT Hydraulic Radius (R) = 0.18 FT Flow Rate (Q) = 1.00 CFS Flow Velocity, V V = Q / A Velocity (V) = 1.59 FPS 4 FPS, non-erosive

32 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 28 Design Goals: Target Rainfall = P E = 1.00 in Target Runoff = Q E = 0.14 in Target Runoff = ESD V = 173 cu ft LOT 2 - GS-2B Grass Swale Design Site Data: Drainage Area (DA) = 15,300 sq ft Impervious Area (I) = 1,450 sq ft Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.14 x 15300) / = 449 cu ft Design Equations: From 2000 Maryland Stormwater Design Manual ESD V = (P E )(R V )(A) Grass Swale Design: Swale Width (W f ) = 2.00' Swale Length (L) = 82' Surface Area (A f ) = 164 sq ft % of DA (2.0% min) = 1.07% Longitudinal Slope (S) = 4.00% (4.0% max) Swale Side Slope (m) = 3 : 1 P E = 1.0'' (P E )(R V )(A IMP ) ESD V = (1)(0.95)(1450) = ESD V = 115 cu ft

33 Determine ESD V Discharge: PAGE: 29 Flow Rate, Q Design Rainfall = 2.6 in Proposed Condition RCN = 64.5 Runoff = 0.32 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/64.5) -2 = 1.1 Ia/P = (1.1)/2.6 IN = tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 758 CSM/IN OR CFS/AC/IN qi = (0.32 IN)(1.185 CFS/AC/IN)(0.35 Ac.) = 0.13 CFS Flow Depth, d Q = (1.49/n)*A*R 2/3 *S 1/2 A = 1/2*d(2*W f +2*m*d) R = A / P P = W f + 2*d*(1+m 2 ) 1/2 Manning's n = 0.15 For Flow Depth d = 0.3 FT 4'' Flow Area (A) = 0.29 SF Wetted Perimetter (P) = 2.78 FT Hydraulic Radius (R) = 0.11 FT Flow Rate (Q) = 0.13 CFS Flow Velocity, V V = Q / A Velocity (V) = 0.44 FPS 1 FPS

34 Determine 10-Year Discharge: PAGE: 30 Design Rainfall = 5.1 in Proposed Condition RCN = 64.5 Runoff = 1.68 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/64.5) -2 = 1.1 Ia/P = (1.1)/5.1 IN = tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 969 CSM/IN OR CFS/AC/IN qi = (1.68 IN)(1.514 CFS/AC/IN)(0.35 Ac.) = 0.9 CFS Flow Depth, d Q = (1.49/n)*A*R 2/3 *S 1/2 A = 1/2*d(2*W f +2*m*d) R = A / P P = W f + 2*d*(1+m 2 ) 1/2 Manning's n = 0.06 Flow Depth d = 0.22 FT Flow Area (A) = 0.6 SF Wetted Perimetter (P) = 3.4 FT Hydraulic Radius (R) = 0.17 FT Flow Rate (Q) = 0.90 CFS Flow Velocity, V V = Q / A Velocity (V) = 1.54 FPS 4 FPS, non-erosive

35 DATE: 11/7/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 31 Site Data: LOT 3 Environmental Site Design (ESD) Sizing Criteria Total Drainage Area (DA): 222,300 SF = 5.1 Acres Total Impervious (I) Area: 8,800 SF = 0.2 Acres = 4.0% Determine Target P E : Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) 22,700 SF 41,900 SF 157,700 SF % of Total DA 0.0% 10.2% 18.8% 70.9% HSG I Area (SF) 5,100 SF 0 SF 3,700 SF HSG %I 0.0% 22.5% 0.0% 2.3% HSG RCN HSG P E * 0.0'' 1.6'' 1.0'' 1.0'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Target RCN = 55 x 10.2% + 70 x 18.8% + 77 x 70.9% = 73.4 Target Rainfall = P E = 1.6'' x 10.2% + 1'' x 18.8% + 1'' x 70.9% = 1.06'' HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.4'' 1.6'' 1.8'' 20% 68 25% % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.0'' 1.2'' % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.0'' 1.2'' 0% % %

36 Proposed Disturbed Area: PAGE: 32 Total Disturbed Area (LOD): 64,300 SF = 1.48 Acres Impervious Area (I) Within LOD: 8,100 SF = 0.19 Acres =.60% Determine Q E : R V = the dimensionless volumetric runoff coefficient = (I) where I is percent impervious cover = (.6%) = 0.16 Q E = Runoff depth in inches that must be treated using ESD practices = P E x R V = 1.06'' x 0.16 = 0.17'' Determine ESD V : ESD V = Runoff volume used in the design of specific ESD practices (P E )(R V )(A) = where A is the drainage area (in square feet) (1.06'')(0.16)(64300) = = 929 CU FT

37 Minimum ESD Target: PAGE: 33 As a minimum, ESD shall be used to address both Re v and WQ v requirements Determine RE V : Re V = Groundwater Recharge volume component of ESD V (S)(R V )(A) = (0.09'')(0.16)(64300) = = 82 CU FT SOIL SPECIFIC RECHARGE FACTOR (S) HSG (S) % AREA (S)(%A) A % 0 B % C % D % COMPOSITE S = Determine WQ V : Wq V = Water Quality volume component of ESD V = 1.0" Eastern Zone and 0.9" Western Zone (P E )(R V )(A) = where A is the drainage area (in square feet) (1'')(0.16)(64300) = = 875 CU FT

38 JOB #: DATE: 11/7/2014 Macris, Hendricks & Glascock, P.A. PAGE: Wightman Road, Suite 0 ESD SUMMARY - LOT 3 TREATMENT IMPERVIOUS UNIT NO. FACILITY DESCRIPTION AREA (SF) AREA (SF) P E (IN) R V ESD V DW-3A Dry Well DW-3B Dry Well DW-3C Dry Well MB-3 Micro-Bioretention 10,650 1, TOTALS 13, , AVG. PE 2.60 R V = (I) (P E )(R V )(A) (ESD V ) ESD V = PE = where I is percent impervious cove (RV)(A)

39 DATE: 11/7/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 35 It is not practicable for all parts of the development area to drain to stormwater facilities. It is therefore necessary to average the treated ESDv from all drainage areas over the entire development area. This is accomplised using the relationship between P E and ESDv such that the ESDv term is the summation of all treated stormwater volumes, while the site data is based on the development area. Determine Avg. Treatment P E for Total Site: P E = (ESD V ) (RV)(A) Treated ESDv = 931 CU FT Disturbed Area (LOD) = 64,300 SF Rv = 0.16 Avg. P E = (931.1) (0.16)(64300) Avg. Treatment P E = 1.06 Average Treatment P E for Development Area (From ESD SUMMARY Sheet) Target P E = Avg. Treatment P E = ESDv Required = ESDv Provided = 1.06'' 1.06'' 929 cu ft 931 cu ft

40 DATE: 11/7/14 CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 36 Design Treatment P E= 1.06'' Use 1.0'' Site Data: LOT 3 Environmental Site Design (ESD) Sizing Criteria Total Drainage Area (DA): 222,300 SF = 5.1 Acres Total Impervious (I) Area: 8,800 SF = 0.2 Acres = 4.0% Determine Reduced RCN: Drainage Area Hydrologic Soil Group (HSG) Distribution HSG A B C D HSG DA (SF) 0 SF 22,700 SF 41,900 SF 157,700 SF % of Total DA 0.0% 10.2% 18.8% 70.9% Site %I 4.0% 4.0% 4.0% 4.0% HSG RCN* Design P E 0.0'' 1.0'' 1.0'' 1.0'' *See Abridged Rainfall Targets/RCN Reductions Table(s) Below Design RCN = 55 x 10.2% + 70 x 18.8% + 77 x 70.9% = 73.4 Design RCN (73.4) < or = Target RCN (73.4) THUS REDUCED RCN = ''WOODS IN GOOD CONDITION'' AND CPv HAS BEEN SATISFIED HYDROLOGIC SOIL GROUP A %I RCN* P E = 1.0'' 1.2'' 0% % % HYDROLOGIC SOIL GROUP B %I RCN* P E = 1.0'' 1.2'' 0% % % HYDROLOGIC SOIL GROUP C %I RCN* P E = 1.0'' 1.2'' 0% % % HYDROLOGIC SOIL GROUP D %I RCN* P E = 1.0'' 1.2'' 0% % %

41 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 37 Design Goals: Target Rainfall = P E = 2.00 Target Runoff = Q E = 1.90 in Target Runoff = ESD V = 380 ft 3 in 75% ESD V = 285 ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.0 in ESD V = 7 ft 3 LOT 3 - DW-3A Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

42 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 38 Design Goals: Target Rainfall = P E = 2.00 Target Runoff = Q E = 1.90 in Target Runoff = ESD V = 380 ft 3 in 75% ESD V = 285 ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.0 in ESD V = 7 ft 3 LOT 3 - DW-3B Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

43 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 39 Design Goals: Target Rainfall = P E = 2.00 Target Runoff = Q E = 1.90 in Target Runoff = ESD V = 380 ft 3 in 75% ESD V = 285 ft 3 Site Data: Drainage Area (DA) = 800 ft 2 Design Equations: From 2000 Maryland Stormwater Design Manual (1) (P E )(R V )(A) ESD V = (2) P E = (ESD V ) (RV)(A) Facility Requirements: For P E = 1.0 in ESD V = 63 ft 3 For P E = 2.0 in ESD V = 7 ft 3 LOT 3 - DW-3C Dry Well Design Facility Design: Trench Width (W) = 10 ft Trench Length (L) = 10 ft Trench Depth (D) = 4.5 ft (Stone Only) Stone Volume (V) = 450 ft 3 (W x L x D) Porosity = 40% Storage Volume = ft 3 (0.4 x V) P E = 2.8 in (Eq. 2)

44 DATE: CHECKED BY: Macris, Hendricks & Glascock, P.A. PROJECT No.: Wightman Road, Suite 0 PAGE: 40 LOT 3 - MB-3 Micro-Bioretention Design Site Data: Drainage Area (DA) = 10,650 sq ft Maximum Runoff Volume: V = (P x R V x A) / = (2.6 x 0.19 x 10650) / = 437 cu ft Upstream ESDv Provided= cu ft Maximum Runoff Volume = 437 cu ft Effective Drainage Area: Upstream ESD V Provided = 0 cu ft or 0% of Maximum Runoff Volume Effective Drainage Area = x 100% = sq ft Design Equations: From 2000 Maryland Stormwater Design Manual ESDv = (P E )(R V )(A) P E = (ESDv)() (Rv)(A) Facility Design: A f = 250 sq ft (2.3 % DA) Bottom Storage Area = 250 sq Elev 0.00' Top Storage Area = 350 sq Elev 0.50' Storage Depth = 0.50' Temp. Ponding Volume = 150 cu ft Planting Media Depth = 3.5 ft (2.0'-4.0') Sand Layer Depth = 0.5 ft Porosity (n) = 0.40 Media Storage Volume = 400 cu ft Total ESDv Provided = 550 cu ft ESDv exceeds Max. Runoff Volume Total ESDv Provided = 437 cu ft P E = ()(ESDv) (Rv)(A) = ()(437) (0.19)(10650) P E = 2.60 in

45 Enhanced (Y or N): N Enhanced Filter - Stone Reservoir Design: PAGE: 41 S = Re V = 0.19 in 32 cu ft A f = 250 sq ft Depth (D) = 1.0 ft Porosity (n) = 0.4 Vol. of Stone = 250 cu ft Vol. of Storage= 100 cu ft P E in Stone Reservoir = ()(ESDv) (Rv)(A) = ()(100) (0.19)(10650) = 0.59 in Total Facility Treatment Provided: ESDv treated by Filter = 437 cu ft ESDv treated by Enhancement = N/A Total ESDv Treatment = 437 cu ft P E treated by Filter = P E treated by Enhancement = Total P E Treatment = 2.60 in N/A 2.60 in

46 Determine 10-Year Discharge: PAGE: 42 Design Rainfall = 5.1 in Proposed Condition RCN = 72.2 Runoff = 2.29 in Proposed Condition Tc = 0.10 Hours Initial Abstraction = Ia = (200/72.2) -2 = Ia/P = (0)/5.1 IN = 0 tc = 0.1 Hours or 0.10 Hours Minimum From TR55: qu = 991 CSM/IN OR CFS/AC/IN qi = (2.29 IN)(1.548 CFS/AC/IN)(0.24 Ac.) = 0.9 CFS Determine 10-Year WSEL: Inlet Weir Crest = 0.50' Inlet Weir Length = 5.0' c = 3.1 Q 10 = 0.9 CFS Q = c * L * H 1.5 H = WSEL 10 = 0.15' 0.65'