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Home My WebLink About1ST PC Hydrology Report 2025-06-24 (2) Thienes Engineering, Inc. CIVIL ENGINEERING ⚫ LAND SURVEYING HYDROLOGY AND HYDRAULIC CALCULATIONS FOR ARROW COMMERCE CENTER – BUILDING 4 ARROW ROUTE AND YELLOWWOOD AVENUE INDUSTRIAL DEVELOPMENT RANCHO CUCAMONGA, CA PREPARED FOR BTC III ARROW ROUTE CC LP 4675 MAC ARTHUR COURT, STE 625 NEWPORT BEACH, CA 92660 P. (949) 892-4900 JUNE 24, 2025 JOB NO. 4021 PREPARED BY THIENES ENGINEERING 14349 FIRESTONE BLVD. LA MIRADA, CALIFORNIA 90638 P. (714) 521-4811 FAX (714) 521-4173 HYDROLOGY AND HYDRAULIC CALCULATIONS FOR ARROW COMMERCE CENTER – BUILDING 4 PREPARED UNDER THE SUPERVISION OF: REINHARD STENZEL DATE R.C.E. 56155 EXP. 12/31/2026 INTRODUCTION A: PROJECT LOCATION The project site is located along the south side of Arrow Route between Interstate 15 and Etiwanda Avenue, in the City of Rancho Cucamonga, California. Please see following page for vicinity map. B: STUDY PURPOSE The purpose of this study is to determine the existing and proposed condition 100-year peak flow rate from the site that drains southerly to two different discharge points which are conveyed southerly under the existing railroad. C: PROJECT STAFF: Thienes Engineering staff involved in this study include: Reinhard Stenzel Brian Weil INTRODUCTION A: PROJECT LOCATION The project site is located along the south side of Arrow Route between Interstate 15 and Etiwanda Avenue, in the City of Rancho Cucamonga, California. Please see following page for vicinity map. B: STUDY PURPOSE The purpose of this study is to determine the existing and proposed condition 100-year peak flow rate from the site that drains southerly to two different discharge points which are conveyed southerly under the existing railroad. C: PROJECT STAFF: Thienes Engineering staff involved in this study include: Reinhard Stenzel Brian Weil James Wickenhaeuser APPENDIX DESCRIPTION A REFERENCE MATERIALS B HYDROLOGY CALCULATIONS C HYDRAULIC CALCULATIONS D DETENTION CALCULATIONS E CATCH BASIN CALCULATIONS F HYDROLOGY MAPS G STORM DRAIN PLANS ONSITE & OFFSITE DISCUSSION The project site encompasses approximately 96.50 acres. There is an additional approximate 14.0 acres of offsite area that is tributary to the project site. The existing condition is generally developed with buildings, stockpiles, and paved surfaces. Landscape in the existing condition is limited to the area surrounding the building in the northeast corner. Proposed improvements to the site consist of the construction of one large industrial warehouse, Building 4, totaling 1,050,861 square feet with truck yards on both easterly and westerly sides, and auto parking generally around the northerly and southerly perimeter of the building. A Street, B Street, and Yellowwood Avenue will be constructed to serve the warehouse and the project sites of four additional future buildings. The future project sites will be rough graded, but no site work will be constructed. Off-Site Drainage There is an existing warehouse type building and storage yard in the adjacent property north of the proposed building 5 that drains to the project site. The existing site (14.0 ac.) will be redeveloped for industrial use. Per hydrology report by SDH & Associates, Inc. revision date May 5, 2023, the approximate 100-year peak flow rate is 44.7 cfs and will discharge at the southeast corner. See Appendix “A” for Hydrology Report by SDH & Associates, Inc. Existing Condition The project site is generally divided into two distinct drainage zones. The eastern portion of the site drains southeasterly, while the western portion of the site drains southwesterly. Both discharge points are along the southern property line. North of the eastern portion of the project site, offsite area drains to a channel along the northern property line (Nodes 100-102, 11.8 acres). The channel doesn’t discharge to a single location, but rather overtops and spills to the project site. The 100-year peak flow rate for this offsite area is approximately 29.9 cfs. The eastern drive aisle from Arrow Route drains southerly through a series of open channels and underground conduits to the southeast portion of the site (Nodes 200-226, 37.6 acres). There is an existing detention basin near the southeast property corner. Runoff is discharged from this basin via a 24” storm drain which daylights out a head wall and continues southeasterly following the existing drainage pattern offsite. The runoff is then conveyed under the railroad via (3) 48” CMP pipes and into an existing channel that continues southerly. The 100-year peak flow rate for the eastern portion of the site is approximately 98.2 cfs. The west portion of the site drains southerly towards the southwest corner of the project site (Nodes 300-314, 61.1 acres). Here the runoff from the existing building along Arrow route and the associated parking/storage areas drain southwesterly towards an existing catch basin. An existing storm drain conveys this runoff westerly and southerly towards an existing headwall into a small basin. The runoff from the areas south of the existing building drains southwesterly towards the southwest corner of the site. The runoff is then conveyed under the railroad via (3) 48” CMP pipes and into an existing channel that continues southerly. The 100-year peak flow rate for the western portion of the site is approximately 147.9 cfs. See Appendix “B” for existing condition hydrology calculations and Appendix "F" for existing condition hydrology map. Proposed Condition In the proposed condition runoff will generally match the existing condition drainage pattern. Runoff from three parcels along Arrow Route and the proposed Building 4 will be collected into a storm drain system (Public Line H) and conveyed to a proposed headwall at the southwest portion of the project site (Nodes 100-316, 64.8 acres). The parcels along Arrow Route will not be developed at this time but have been modeled as commercial land use to estimate the future developed condition runoff. Runoff from Building 4 is detained at a higher proportion than is required so the future developments on the three parcels along Arrow Route will not need to detain peak flows. Runoff from the easterly half of Building 4 will drain to a series of catch basins in the easterly truck yard (nodes 200-206). A private onsite storm drain (Line G) will convey stormwater southerly then westerly through the southerly drive aisle. Line G will confluence with Line F and the stormwater will ultimately drain through the proposed headwall at node 316. The undetained 100-year peak flow rate from the easterly portion of the site will be approximately 73.6 cfs. Runoff from the westerly half of Building 4 will drain to a series of catch basins in the westerly truck yard (nodes 300-312). A private onsite storm drain (Line F) will convey Impervious Existing Area Summary Table Nodes Area (ac) Land Use Impervious % 100-102 3.8 Commercial 0.9 8.0 Natural Poor Cover “Barren” 0.0 200-226 9.2 Commercial 0.9 28.4 Natural Poor Cover “Barren” 0.0 300-314 5.3 Commercial 0.9 55.8 Natural Poor Cover “Barren” 0.0 stormwater southerly towards the proposed headwall. The undetained 100-year peak flow rate from the westerly portion of the site will be approximately 75.5 cfs. A portion of Yellowwood Avenue, A Street, and B Street will drain to catch basins within the public right of way and to Public Line H. Storm drain stubs will be provided for the future development of the three parcels along Arrow Route. Line H will convey runoff from the streets and the three parcels westerly through B Street then southerly in A Street to the proposed headwall at the southwest portion of the site (nodes 100-316). The headwall will contain two outlet pipes, one will be Public Line H and the other is onsite Line F. The 100-year undetained peak flow rate through the outlet structure, including both storm drains, will be approximately 200.2 cfs. The south easterly parcel will not be developed at this time, however the public storm drain in Yellowwood Avenue and A Street surrounding the parcel will be constructed. A stub will be built for the future development of the project site. Public Storm Drain Line B will convey stormwater from A Street, south of the future development, easterly towards the stub and confluence with Public Line C. Runoff from a portion of Yellowwood Avenue and A Street north of the project site will drain to public catch basins and into Public Line C. The storm drain will convey the runoff easterly then southerly in A Street to the south easterly corner of the project and the confluence with Line B. The future development is expected to detain stormwater to mimic the existing condition, so the site was modeled using the existing condition land use. A flow path was assumed that represents the longest route stormwater would take in the future condition. The 100-year peak flow rate from the streets and the south easterly parcel to Public Storm Drain Line B will be approximately 88.8 cfs. As mentioned in the “Off-Site Drainage” section of this report, there is an existing warehouse type building and storage yard in the adjacent property north of the proposed building 5 that drains to the project site. The existing site (14.0 ac.) will be redeveloped for industrial use. Per hydrology report by SDH & Associates, Inc. revision date May 5, 2023, the approximate 100-year peak flow rate is 44.7 cfs and will discharge at the southeast corner. The total 100-year peak flow rate to Public Storm Drain Line B, including off-site runon, will be approximately 133.5 cfs (88.8 cfs + 44.7 cfs) See Appendix “A” for the SDH & Associates study, Appendix "B" for proposed condition hydrology calculations and Appendix "F" for proposed condition hydrology map. Detention Analysis Onsite storm flow detention will be utilized to reduce the proposed condition flow rate below the existing condition rate. The easterly and westerly truck yard areas of Building 4 will provide the storage volume, storm drain size restrictions reduce the discharge. A small area unit hydrograph was established for the tributary area to the truck yards. A rating curve was developed hydraulic calculations with varying flow rates to determine the elevation of the HGL in the truck yard and therefore the ponding water surface elevation. The discharge from the truck yard on the east side of Building 4 (Nodes 200-206, 18.31 acres) is reduced from 71.4 cfs to 22.6 cfs with a remaining volume of 0.679 ac-ft temporarily stored in the truck yard at a depth of about 0.64’. This represents a 48.8 cfs or 68% reduction in the 100-year peak flow rate. The discharge from the truck yard on the west side of Building 4 (Nodes 300-312, 21.13 acres) is reduced from 59.4 cfs to 23.3 cfs with the remaining volume of 0.862 ac-ft temporarily stored in the truck yard at a depth of about 0.74’. This represents a 36.1 cfs or 61% reduction in the 100-year peak flow rate. Detention in the two truck yards will reduce the 100-year peak flow rate by a total of 84.9 cfs (48.8 cfs + 36.1 cfs). The existing condition total 100-year peak flow rate is approximately 246.1 cfs (98.2 cfs+147.9 cfs). The detained 100-year proposed condition flow rate will be approximately 219.6 cfs (88.8 cfs+130.8 cfs). This represents an 11% reduction in the 100-year existing condition peak flow rate. Due to this reduction, the proposed development will not negatively impact downstream facilities. See Appendix “D” for detention calculations. Summary The following is a summary of the existing condition and detained proposed condition 100-year site runoff. Detention Results Summary Table Nodes Area (ac) Undetained Q100 (cfs) Detained Q100 (cfs) Reduction Q100 (cfs)(%) 200-206 18.31 71.4 22.6 48.8 300-312 21.13 59.4 23.3 36.1 Total 39.44 130.8 45.9 84.9 Proposed Condition Q100 Reduction Total From Site - Nodes 100-316 (cfs) 200.2 115.3 58% Existing Condition Proposed Condition Reduction in Q100 (cfs) Reduction in Q100 (%) Easterly Outlet 98.2 88.8 -9.4 -10% Westerly Outlet 147.9 130.8 -17.1 -12% Methodology The hydrology calculations were computed using the San Bernardino County Rational Method Program (by AES software). The detention analysis was computed using the San Bernardino County Flood Routing Analysis (by AES Software). The soil type is “A” per the San Bernardino County Hydrology Manual. Total 246.1 219.6 -26.5 -11% APPENDIX A REFERENCE MATERIALS PROJECT SITE SOIL GROUP A PROJECT SITE 1.4" PROJECT SITE 3.75" PROJECT SITE 8.2" 2.1"/2=1.05" 30 MIN. 6.1"/12=0.51" 5 MIN 1.4" 1 HR 100 1.4" 0.60" ARROW AND JUNEBERRY ARROW AND JUNEBERRY TEI JOB NUMBER 4021 3.75" 6 HR. 1.4" 1 HR. 2.5" 3 HR. PRELIMINARY DRAINAGE STUDY (HYDROLOGY AND HYDRAULICS) FOR ARROW ROUTE INDUSTRIAL (PRELIMINARY ENGINEERING) CITY CASE #: DRC2022-00101 Job Number 2125 March 2, 2022 Revised: May 5, 2023 PRELIMINARY DRAINAGE STUDY (HYDROLOGY AND HYDRAULICS) FOR ARROW ROUTE INDUSTRIAL (PRELIMINARY ENGINEERING) CITY CASE #: DRC2022-00101 Job Number 2125 _______________________________________________ Nobu Murakami, P.E. R.C.E. #78149 Exp. 09/30/2023 Prepared for: Newcastle Partners 4740 Green River Road, Suite 110 Corona, CA 92880 Telephone: (951) 582-9800 Prepared by: SDH & Associates, Inc. 27363 Via Industria Temecula, California 92590 Telephone: (951) 683-3691 March 2, 2022 Revised: May 5, 2023