HYDROLOGIC-HYDRAULIC STUDY ISABELLA OCEAN RESIDENCES ISLA VERDE, CAROLINA, PR

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2 HYDROLOGIC-HYDRAULIC STUDY ISABELLA OCEAN RESIDENCES ISLA VERDE, CAROLINA, PR 1 INTRODUCTION 1.1 Project Description and Location Isabella Ocean Residences is a residential development to be constructed on a acre parcel located on Isla Verde Avenue in the municipality of Carolina. Figure 1 shows the project location on the San Juan topographic quadrangle. The project will consist of a multi-story building with common areas, recreational spaces and a multi-level underground parking lot. The site is presently occupied by a single-family residence and a parking lot that will be demolished to develop the residential project. 1.2 Scope and Purpose of Study This document constitutes the hydrologic-hydraulic study for the proposed project. It has been undertaken to determine the required stormwater detention volume for the proposed development to comply with Puerto Rico Planning Board Regulation #3, section 15, which requires that peak site runoff under the proposed condition not exceed the existing condition peak discharge. It also provides the hydraulic dimensions for the stormwater control structure. This report should be used as the basis for civil design of the project. 1.3 Report Limitations and Warnings It shall be the responsibility of the site engineer or the project s geotechnical consultant to adapt the hydraulic design recommendations to the soil and other conditions at the site in any matters concerning slope stability, conflicts with other infrastructure, etc. 1.4 Authorization Mr. Joel Katz, President of IJK Inc., has authorized preparation of this report, in representation of the owner, through an agreement with Gregory Morris Engineering

3 1.5 Personnel Involved in Project The professionals of Gregory Morris Engineering involved in the realization of this study were: Gregory L. Morris P.E. José D. Miranda P.E. The following parties were involved in the project: Designer: LRA Architects - 2 -

4 2 STUDY AREA DESCRIPTION 2.1 Topography and Water Bodies Site elevations range between 2.67 m and 3.24 m (msl). Due to topographic characteristics runoff generated on the site drains superficially toward Isla Verde Avenue and enters the storm sewer system though a curb inlet adjacent to the site s existing entrance. No offsite runoff enters the property. There are no water bodies or sinkholes on the site, but the Atlantic Ocean borders the site on the north. Figure 2 shows the topographic features of the site. 2.2 Prior Studies The Isabella Ocean Residences site is classified as Zone -X in the FEMA Flood Insurance Rate Map (FIRM). A copy of the FEMA Floodway map (Panel 52, revised June 2, 1999) is presented as Figure 3. The project area is not classified as floodable by the Puerto Rico Planning Board Flood Zoning Map (see Figure 4). The regulatory flood elevation presented on the maps is 2.40 m-msl due to storm surge. There are no prior hydrologic-hydraulic studies for the site. 2.3 Field Data This study uses topographic survey data provided by Surveyor Eugenio López Encarnación. The survey was performed during the month of June 2003 and is referenced to mean sea level. A copy of the topographic data is included in the back pocket of this report. 2.4 Field Visit The site was visited during the month of November, Observed conditions are summarized below. The site consists of two properties. The east property consists of a single residence with significant green area. The west property is a paved parking lot. There is no storm sewer system on the site. The ground slopes to the south and runoff generated at the site drains superficially toward Isla Verde Avenue. This runoff reaches the Isla Verde Avenue storm sewer system through a curb inlet located close to the site s entrance

5 3 STUDY APPROACH 3.1 Conceptualization of the Hydraulic System The hydraulic system for the existing condition was conceptualized as one on-site basin (representing the project site) draining to a node (representing the curb inlet at Isla Verde Avenue) where the peak discharge produced by the basin was determined. For the post-development condition, land use parameters and drainage patterns were altered to account for the proposed site plan and change in hydrologic parameters at the site, plus the proposed detention structures. 3.2 Study Approach and Methodology A detention analysis requires the generation of storm hydrographs showing the variation of runoff over time. The runoff hydrographs in this analysis were generated using the Soil Conservation Service unit hydrograph methodology as implemented in the ICPR model. Detention volume temporarily stores runoff and releases it more slowly through a hydraulic structure. Sizes of the required storage and hydraulic configuration of the outlet structure were determined by hydrologic and hydraulic modeling, comparing existing and proposed condition runoff hydrographs at the point of analysis. The study has been performed using the ICPR unsteady flow hydrologic-hydraulic modeling system (Streamline Technologies v3.0, Winter Park, Florida). The ICPR model dynamically routes stormwater through open channels, closed conduits and detention ponds. The program s solution algorithm allows it to simulate a variety of complex conveyance systems. Each node in ICPR represents a control volume. Change in storage for each node is calculated based on the difference between inflows and outflows at each time step during the simulation period. The change in storage is used to determine elevations at each node at the end of each time step. Flow through each link is calculated from the known elevations at each end of the link and the hydraulic properties of the link. The hydrologic and hydraulic analysis was performed to determine the discharge hydrographs for 2-, 10-, and 100- year return intervals storms from the area under existing and proposed land use conditions

6 4 HYDROLOGIC ANALYSIS 4.1 Curve Number and Time of Concentration Soils in the area were not surveyed in the Soil Survey of San Juan Area of Puerto Rico (Boccheciamp, 1977) because it is an urban area. Figure 5 shows a partial reproduction of the soil survey where the project is located. Soil classification was adopted from the geotechnical exploration performed at the site area by Geo- Engineering and site inspection. Soils in the project area consist of beach sands and are in hydrologic class A which indicates they have a low runoff potential. Antecedent Moisture Condition II was used. Table 1 and Table 3 show the Curve Numbers used in this analysis for existing and proposed conditions, respectively. Table 1: Curve Number Calculations for Project Site under Existing Conditions Soil Type Hydrologic Soil Group Land Use Area (m 2 ) Curve Number Tropopsamments A Grass, brush 1, Tropopsamments A Paved Area 2, Weighted Curve Number 88 Table 2: Curve Number Calculations for Drainage Areas under Proposed Conditions Drainage Area Land Use Area (m 2 ) Curve Number Roof 1 Paved Roof 2 Paved Remainder Site Paved/some grass 2, The time of concentration is the time required for a drop of water falling on the most distant point of the watershed to influence discharge at the watershed exit. The time of concentration was calculated using Soil Conservation method (TR-55). For sheet flow calculation the following equation was used: t c = (0.007*n 0.8 *L 0.8 ) / (P 2 0.5*S 0.4 ) where: t c = time of concentration (minutes) n = Manning s roughness coefficient - 5 -

7 L = flow length (ft) P 2 = 2-year, 24-hour rainfall (in) S = slope of hydraulic grade line (land slope, ft/ft) The time of concentration for the entire project site under existing conditions is 5 minutes. Table 3 shows the results of the time of concentration calculations for the three different drainage areas used in the proposed condition model. Table 3: Time of Concentration Calculations for Drainage Areas under Proposed Conditions Drainage Area Time of Concentration (minutes) Roof 1 3 Roof 2 3 Site other than roof Rainfall The study used the 24-hour rainfall depths reported by the US Department of Commerce (1961) in Technical Paper-42, and the Soil Conservation Service Type-II 24- hour rain distribution. The rainfall depths at the project site are shown in Table 4. Table 4: 2-, 10- and 100- year Rainfall Depths (TP-42) at Project Site Return Interval Rainfall Depth 2-years 10-years 100-years 5 inches 7 inches 10 inches 4.3 Results of Hydrologic Analysis The peak discharges in this analysis were computed by the Natural Resources Conservation Service s unit hydrograph methodology with a peaking factor of 484. Table 5 presents peak discharges reaching Isla Verde Avenue for existing and proposed land use conditions, without detention storage

8 Table 5: Existing and Proposed Condition (without detention storage) Peak Discharges Peak Discharge (ft 3 /s) Condition 2-year 10-year 100-year Existing Proposed Verification of Hydrology Peak discharges for basins with areas less than 150 acres were verified using the rational method: Q = C*I*A where: Q = peak discharge (ft 3 /s) C = runoff coefficient I = rainfall intensity (in/hr) A = drainage area (acres) Parameter values were obtained from Normas de Diseño para Sistemas de Alcantarillado Pluvial (Puerto Rico Planning Board, 1975). Table 6 shows the parameters used and results obtained with the Rational Method. Table 6: Parameters used for Hydrology Verification with Rational Method Condition Rainfall Intensity (in/hr) Runoff Coefficient Peak Discharge (ft 3 /s) Existing Proposed Table 7 compares 100-year peak discharges obtained by ICPR and those obtained with the rational method. Based on verification computations, the peak discharges produced by ICPR were accepted as reasonable. Table 7: Verification of Hydrology Results Condition 100-year Peak Discharge (ft 3 /s) ICPR Rational Method Existing Proposed

9 5 HYDRAULIC ANALYSIS Three ICPR models were prepared to study the effects of the proposed project, one for the existing condition and two for the proposed condition. The existing condition model consists of the onsite basin draining into the Isla Verde Avenue curb inlet. Under proposed conditions runoff will drain from the roofs into the proposed detention system, and the rest of the site drains directly into the street. Two different detention structure configurations were analyzed. Figure 6 shows a schematic node-link configuration for existing conditions. Figure 7 and Figure 8 show detention structure Alternative 1 and Alternative 2, respectively. 5.1 Existing Condition Model The existing condition model simulates existing hydrologic conditions on the project site. The model consists of the project site basin discharging into the Isla Verde Avenue curb inlet located in front of the property. Appendix A shows input data and modeling results for the existing condition. 5.2 Proposed Condition Models The purpose of the proposed condition model is to size the detention storage necessary to insure that the post-development discharge downstream the site does not exceed the existing condition discharge. Roof runoff is directed into the detention structure. Figure 9 shows the proposed project layout. The total roof area was divided into two identical drainage areas, each discharging into its own identical detention structure. Each detention structure (for both Alternative 1 and Alternative 2) consists of flow diversion box and detention tank. All discharge generated by the roof should be collected in the flow diversion box. A portion of this flow will discharge through the floor orifice in the flow diversion box and excess flow will pass over the weir and into the detention tank. The total discharge exiting the diversion box and detention tank for each portion of the roof, plus the total discharge exiting the rest of the site, will not exceed the existing condition discharge. The detention structures were modeled with the parameters presented in Section 6.1 of this report. Appendix B and C shows input data and modeling results of the proposed condition model for Alternative 1 and Alternative 2, respectively

10 Table 8 presents the existing and proposed condition discharges produced by the project site. Table 8: Existing and Proposed Conditions Peak Discharge Condition Peak Discharge (ft 3 /s) 2-year 10-year 100-year Existing Proposed Alternative 1 Proposed Alternative

11 6 HYDRAULIC DESIGN RECOMMENDATIONS 6.1 Detention Structure Design Parameters The detention system for the proposed project was modeled as a combination of diversion boxes and detention tanks. The roof will be divided into two halves, each draining into its own detention structure. Runoff from the roof will enter a flow diversion box with and orifice in the floor and a rectangular weir at one end. The orifice passes flows less than the 2-year discharge directly to the street drainage, and portions of higher flow are passed into the detention structure via a rectangular weir. The detention tank outlet structure consists of a standpipe and a two orifice to control the flow rate and comply with the Puerto Rico Planning Board Regulation #3. Two orifices will be placed at different elevations to mitigate the rainfall events of different recurrences. The pond s outlet structure will drain into an 8-inch pipe that will discharge into the street. The diversion box and detention tank for Alternative 1 will be placed one next to the other, and share the same top elevation. The diversion box and detention tank for Alternative 2 will not be placed one next to the other, and will be connected to each other through a 10-inch pipe. Figure 10 and Figure 11 show schematic drawings of the proposed detention systems Alternative 1 and Alternative 2, respectively. The parameters shown in Table 9 and Table 10 should be used as the basis of design for the detention tanks and diversion boxes for Alternative 1, respectively. The parameters shown in Table 11 and Table 12 should be used as the basis of design for the detention tanks and diversion boxes for Alternative 2, respectively. The entire detention system for the two alternatives consists of two identical detention tanks and diversion boxes, one for each half of the roof area

12 Table 9: Alternative 1 Proposed Detention Tank Parameters Parameter DETENTION TANK Depth Value 2 meters Top/Bottom Area 2 meters 2 Bottom Elevation Maximum 100-year Water Depth DETENTION TANK OUTLET STRUCTURE 2-YEAR ORIFICE Diameter Invert Elevation above bottom 10-YEAR ORIFICE Diameter Invert Elevation above bottom 100-YEAR STANDPIPE Diameter Invert Elevation above bottom OUTLET PIPE Diameter Invert Elevation above bottom 2.5 m-msl 1.9 m 3 inches 0 meter 3 inches 1 meter 6 inches 1.8 meters 8 inches 0 meters

13 Table 10: Alternative 1 Proposed Diversion Box Parameters Parameter DIVERSION BOX Depth Value 1 meters Top/Bottom Area 1 meters 2 Bottom Elevation above Detention Tank Maximum 100-year Water Depth RECTANGULAR WEIR TO TANK Span Invert Elevation above bottom OUTLET TO STREET ORIFICE Diameter Invert Elevation above bottom OUTLET PIPE Diameter 1 m 0.9 m 0.5 meters 0.7 meters 3 inches 0 meters 6 inches

14 Table 11: Alternative 2 Proposed Detention Tank Parameters Parameter DETENTION TANK Depth Value 2 meters Top/Bottom Area 2 meters 2 Bottom Elevation Maximum 100-year Water Depth DETENTION TANK OUTLET STRUCTURE 2-YEAR ORIFICE Diameter Invert Elevation above bottom 10-YEAR ORIFICE Diameter Invert Elevation above bottom 100-YEAR STANDPIPE Diameter Invert Elevation above bottom OUTLET PIPE Diameter Invert Elevation above bottom 2.5 m-msl 1.9 m 2.5 inches 0 meters 4 inches 0.8 meters 6 inches 1.8 meters 8 inches 0 meters

15 Table 12: Alternative 2 Proposed Diversion Box Parameters Parameter DIVERSION BOX Depth Value 1 meters Top/Bottom Area 1 meters 2 Bottom Elevation Maximum 100-year Water Depth RECTANGULAR WEIR TO TANK Span Invert Elevation above bottom PIPE BETWEEN BOX AND TANK Diameter Upstream Invert Elevation above box bottom Downstream Invert Elevation above tank bottom OUTLET TO STREET ORIFICE Diameter Invert Elevation above bottom OUTLET PIPE Diameter As desired by architect 0.6 m 0.5 meters 0.5 meters 10 inches 0 meters 1.8 meters 3 inches 0 meters 6 inches

16 7 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 1. The detention systems for Alternative 1 and Alternative 2 have been sized for this project so that the existing condition peak discharges for the 2-, 10- and 100-year events are not exceeded under proposed conditions. 2. It is the responsibility of the site engineer to direct all of the stormwater from the roof area into the proposed system. 3. The detention outlet structures must be inspected periodically to avoid obstruction with debris. The boxes and tanks should also be maintained periodically to remove accumulated sediment. 4. Hydraulic design parameters and recommendations are provided in Section 6 of this report. I hereby certify that the document Hydrologic-Hydraulic Study, Isabella Ocean Residences, Isla Verde, Carolina, Puerto Rico has been prepared in accordance with the best hydrologic and hydraulic practices as described in this document and that, based on the studies and field measurements provided by other parties, results are true and correct. Certified today October 21, 2004 Gregory L. Morris,P.E.,Ph.D

17 8 REFERENCES Boccheciamp, Rafael A "Soil Survey of San Juan Area of Puerto Rico." U.S. Soil Conservation Service. San Juan PR. Maidment David R Handbook of Hydrology. McGraw-Hill, Inc. New York Puerto Rico Planning Board, Normas de Diseño para Sistemas de Alcantarillado Pluvial. San Juan PR. Singhofen P.J., and L.M. Eaglin ICPR Advanced: User s Manual. Streamline Technologies Inc., Winter Park, FL US Department of Agriculture, Soil Conservation Service Technical Release 55 (Urban Hydrology for Small Watersheds). Washington DC. US Department of Commerce Technical Paper #42. Washington DC

18 TABLE OF CONTENTS 1 INTRODUCTION Project Description and Location Scope and Purpose of Study Report Limitations and Warnings Authorization Personnel Involved in Project STUDY AREA DESCRIPTION Topography and Water Bodies Prior Studies Field Data Field Visit STUDY APPROACH Conceptualization of the Hydraulic System Study Approach and Methodology HYDROLOGIC ANALYSIS Curve Number and Time of Concentration Rainfall Results of Hydrologic Analysis Verification of Hydrology HYDRAULIC ANALYSIS Existing Condition Model Proposed Condition Models HYDRAULIC DESIGN RECOMMENDATIONS Detention Structure Design Parameters SUMMARY, CONCLUSIONS AND RECOMMENDATIONS REFERENCES

19 List of Figures and Appendix Figure 1: Location Map Figure 2: Topographic Features of Site Figure 3: FEMA FIRM Map Panel 224B, dated July 19, 1982 Figure 4: PR Planning Board Flood Zone Map Sheet 39D, dated February 11, 1988 Figure 5: Soil Map of Puerto Rico Area of Southern Puerto Rico, Sheet 23 Figure 6: Existing Condition Node/Link Diagram Figure 7: Alternative 1: Proposed Condition Node/Link Diagram Figure 8: Alternative 2: Proposed Condition Node/Link Diagram Figure 9: Proposed Project Layout Figure 10: Schematic Drawing of Alternative 1 Proposed Detention Pond Figure 11: Schematic Drawing of Alternative 2 Proposed Detention Pond Appendix A: Input and Results of ICPR Model for Existing Condition Appendix B: Input and Results of ICPR Model for Proposed Condition Alternative 1 Appendix C: Input and Results of ICPR Model for Proposed Condition Alternative

20 List of Tables Table 1: Curve Number Calculations for Project Site under Existing Conditions Table 2: Curve Number Calculations for Drainage Areas under Proposed Conditions Table 3: Time of Concentration Calculations for Drainage Areas under Proposed Conditions Table 4: 2-, 10- and 100- year Rainfall Depths (TP-42) at Project Site Table 5: Existing and Proposed Condition (without detention storage) Peak Discharges Table 6: Parameters used for Hydrology Verification with Rational Method Table 7: Verification of Hydrology Results Table 8: Existing and Proposed Conditions Peak Discharge Table 9: Alternative 1 Proposed Detention Tank Parameters Table 10: Alternative 1 Proposed Diversion Box Parameters Table 11: Alternative 2 Proposed Detention Tank Parameters Table 12: Alternative 2 Proposed Diversion Box Parameters

21 FIGURES

22 N SITE Figure 1: Isabella Ocean Residences Site Location in USGS Topographic Quadrangle of San Juan.

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24 N SITE Figure 3: FEMA Floodway Map, Panel (June 2, 1999)

25 N SITE Figure 4: Puerto Rico Planning Board Floodway Map (9-B: June 1, 1999)

26 N SITE Figure 4: Isabella Ocean Residences Watershed Limits.

27 N SITE NOT SURVEYED NOT SURVEYED Figure 5: Soil Survey of San Juan Area of Eastern Puerto Rico. US Department of Agriculture, Soil Conservation Service Rafael A. Boccheciamp, 1977.

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34 Appendix A Input and Results of ICPR Model for Existing Condition

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38 Appendix B Input and Results of ICPR Model for Proposed Conditions: Alternative

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50 Appendix C Input and Results of ICPR Model for Proposed Condition: Alternative

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