HIGH SCHOOL NO. 4

FINAL DRAINAGE REPORT

Town, Arizona

Prepared for:

Unified School District

Prepared by:

Engineering

North Road

Arizona

Job No. 24007

June 2005
Revised Aug 2005

TABLE OF CONTENTS

1 Report Objective	1

2 Site Description	1

3 Collection	1

4 Retention	2

4.1 Retention Disposal	2

5 Site Outfall and Finished Floors	2

6 Previous Studies and Reference Materials	2

7 Hydrologic Calculations	3

8 Hydraulic Calculations	3

8.1 Inlet capacities	3

8.2 Storm drain hydraulics	3

8.3 Storm drain network	3

APPENDIX A, STORM DRAIN CALCULATION TABLE AND KEY MAP	4

INTRODUCTION

Report Objective

The purpose of this report is to document research and present calculations supporting drainage improvements constructed as part of the High School No. 4 project.

Site Description

High School No. 4 is proposed to occupy a 68-acre site located on the south side of Creek Road between Vista Drive and Green Road in Town. The site is an existing dairy. The proposed Sand Estates residential subdivision is immediately west and south of this project, unsubdivided suburban ranch parcels are east, and farm fields are north across Creek Road.

OFF-SITE DRAINAGE

The general direction of drainage in the area of this project is slightly north of west. East-west streets drain west and north-south streets drain north. The contributing offsite drainage area to the east side of the site along 15th street is ½ square mile, extending east to the RD Canal and East Floodway. All off-site drainage that arrives at 15th Street will be directed by the elevated street crown northward to Creek Road, where it will either enter the RD irrigation tailwater system or continue westward on Creek Road. If there is available capacity in the site retention pipes, they will intercept some of this runoff. The rest will continue past the project westward on Creek Road. This project is designed to collect and retain runoff from within the site boundaries and the adjacent offsite street.

The lowest building floor upstream of the site is at elevation 1289.76

FEMA FLOODPLAIN

This site lies in flood zone X (shaded) on FEMA Flood Insurance Rate Map dated July 2001. Zone X (shaded) on this map “includes areas of 500-year flooding; areas of 100-year flooding with depths less than 1 foot or drainage area less than 1 square mile; and areas protected by levees from 100-year flood. No flood insurance is required for this area.”

ON-SITE DRAINAGE

Collection

Creek Road and 15th Street are drained by MAG 534 or MAG 523 catch basins and CSP storm drains to underground retention pipes. These catch basins and storm drains are designed to convey the 10-year peak flow per Town requirements.

The campus and parking lots are drained by private storm drains to the site retention basins. They are designed to carry the 2-yr flow.

2-year and 10-year storm drain and inlet calculations are tabulated and a key map is included in Appendix A.

Retention

Retention for storm water runoff from the site is provided five areas including two play field areas and three underground pipes as shown on the retention calculations table below.

Retention Disposal

Disposal calculations are shown below. A copy of the percolation test report is included in Appendix B.

Site Outfall and Finished Floors

The ultimate outfall for this site is the over the south return top of curb at Baha Drive and Creek Road at the northwest corner of this site, elevation 1284.2. From there the existing terrain slopes west on Creek Road. The lowest finished floor on the site is 1288.48, 4 feet above the site outfall. Each building and its surrounding area are designed to keep outfalls 0.30’ below the finished floor of the buildings.

DATA ANALYSIS METHODS AND ASSUMPTIONS

Previous Studies and Reference Materials

The following studies and materials were consulted in the preparation of this report:

County Assessor GIS web server.

FEMA online Map Store

Hydrologic Calculations

Peak flows for storm drain calculations were determined using the Rational Method with

runoff coefficients taken from the Town Procedure Manual,

times of concentration calculated per H.E.C. #12 with 2 minute sheet flow time added for offsite street cross flow, 5 minute sheet flow time added for onsite areas, and a minimum 10 minute Tc used in calculating intensity.

rainfall intensity equations derived per H.E.C. #12 from NOAA Atlas 2 maps for the Gilbert area.

Because storm drains have submerged outlets and will be full at all flows, leaving no surplus storage routing capacity, no storm drain component was added to time of concentration.

Hydraulic Calculations

Inlet capacities

In-sump area drain capacities on site were calculated per HEC #12 with capacity reduced per MCFCD drainage design manual for clogging allowance.

Q=EFF*3.0*P*d^1.5 where EFF is the efficiency after clogging, P is the inlet perimeter, and d is the ponding depth per HEC #12.

Storm drain hydraulics

Storm drain friction losses were calculated using the Manning equation with n=0.012. Storm drain junction losses were estimated with minor loss coefficients varying from 0.5 at a 45 degree bend to 4.0 at an inlet. Starting hydraulic grade lines were calculated based on 40% of 50-year, 24-hour volume in basins at the time of 10-year peak flow.

Storm drain network

The storm drain network was simplified by modeling many roof drain leaders as though they enter the system at the next junction upstream. To make this simplification conservative, the total junction loss for the roof drain entrance was added to the upstream junction loss. Also, most pipes smaller than 12” were not modeled.

APPENDIX A, STORM DRAIN CALCULATION TABLE AND KEY MAP

High School No. 4 Final Drainage Report	Page 3

Old Stone Ranch Elementary School No. 21 Final Drainage Report	Page 3

DRAINAGE REPORT

Tom Haws

1999-12-14T13:59:00

Thomas Gail Haws

Thomas Gail Haws