stormwater master plan nw 21-50-1-4 preliminary ......2.2 design criteria based on the...

Submitted to:

REINHART PROPERTY MANAGEMENT

Stormwater Master Plan NW 21-50-1-4

Preliminary Engineering Report

June, 2007

Submitted by:

f7 somencl Inc.El better woter I better wo.ld

Dale: June '12, 2007

Relnharl Property Managsment

Ailention: JasonReinhart

REi Stormryater Management Plan Preliminary Engin€eing Reportsw 21-50-14

Dear Sir,

We are pleased to submit this pre-design report for the Stormwater Management Plan for theNW 21-50-'14.

We look to ard to your comments priof to continuing with lhe design. Should you wishdiscu8sion while reviewing the document, pleas€ contacl me al482-2557.

Sinceraly,

1500 Eakef Cenfe, 10025-106 StreetEdmonbn, AB. TsJ 1G3

PH: (780) 482-2557FX: (780) 48?-2538wrvw' s€meng.aom

dave. [email protected]

Reinhart Property Management - Country Residential Subdivision

TABLE OF CONTENTS Table of Contents

1 SITE DESCRIPTION ...................................................................................1.1 1.1 Introduction ....................................................................................................... 1.1 1.2 Site Description................................................................................................. 1.1

2 PAST STUDIES AND DESIGN STANDARD ..............................................2.2 2.1 Past Studies...................................................................................................... 2.2 2.2 Design Criteria .................................................................................................. 2.2

3 PROPOSED STORMWATER MANAGEMENT PLAN................................3.1 3.1 Internal Drainage .............................................................................................. 3.1 3.2 Stormwater Facility ........................................................................................... 3.1 3.3 Stormwater Quality ........................................................................................... 3.2

4 FURTHER REQUIREMENTS ......................................................................4.1

5 CORPORATE AUTHORIZATION ...............................................................5.2

APPENDIX A – Figures APPENDIX B – HEC HMS Results

Reinhart Property Management - Country Residential Subdivision 1.1

1 SITE DESCRIPTION

1.1 Introduction

Reinhart Property Management is planning a country residential subdivision, within the County of Vermilion River No. 24. They have retained Sameng Inc. to provide a stormwater management plan.

This report outlines the proposed stormwater management strategy for the proposed subdivision.

1.2 Site Description

The study area is located north of Lloydminster within the County of Vermilion Riveron the remainder of NW 21-50-1-W4M (parcel). As shown in Figure A.1, this 60 hectare area is located within the Big Gully Stormwater Master Plan.

It has positive drainage from west to east but has a ridge dividing the southern portion of the quarter (Figure A.1). There is little offsite drainage passing through the subject parcel and there are only very small semi-permanent water bodies within the site (see Figure A.2). All runoff from this parcel eventually flows to Big Gully Creek through the same drainage course as the Hawkstone Subdivision.

A significant pipeline corrider runs diagonally across the quarter section and may present constraints of the development of the drainage network.


2 PAST STUDIES AND DESIGN STANDARD

2.1 Past Studies

The Big Gully Stormwater Master Plan was completed by Sameng Inc in 2006. This study’s primary objective was to recommend stormwater design parameters for the Big Gully Basin.

The area encompassed by the Big Gully Stormwater Master Plan includes the proposed this proposed subdivision. Therefore the recommended maximum post development discharge rate of 4.0 L/s/ha was accordingly adopted for this management plan.

The Big Gully Plan also identifies the Durness Project downstream of this subdivision. It will be necessary to ensure that at least the downstream portion of that project be constructed prior to or in conjunction with this project.

2.2 Design Criteria

Based on the recommendations of the Big Gully Stormwater Master Plan and discussions with Alberta Environment, the following design criteria were used in developing the Stormwater Management Plan.

1. Site drainage will be collected and controlled by a stormwater management system. Alternatively this may be a single facility or two ponds if required. The maximum rate of discharge, under post development conditions will not exceed 4.0 L/s/ha. The stormwater pond volume will be sized to contain the more severe of the 100-year 24-hour storm (Huff Distribution) or the 100-year 4-hour storm (Chicago Distribution). The August 2005 event will be modeled for verification of design.

2. Design of the stormwater management facility will improve the quality of the discharge water. The primary parameters to consider will be settleable solids and floatables.


3 PROPOSED STORMWATER MANAGEMENT PLAN To assist in the development of the Stormwater Management Plan (SWMP) for this project a computer model was developed. This model was created using the Hydrological Engineering Center’s Hydrological Modeling System (HEC-HMS) Version 3.1.2. The key considerations are described in the following sections.

3.1 Internal Drainage

The ditches associated with the eternal roads will collect stormwater from the proposed subdivision and deliver to the proposed stormwater pond. Ideally the pond will be located in the along the east boundary of the subdivision as shown in Figure A.3. The pond will be drained by a new ditch along the east boundary of the property to the natural drainage draw located near the southeast corner of the subdivision. This scheme which would see virtually all of the lands routed through the proposed Stormwater Pond is referred to as Scenario 1.

Alternatively, if the natural ridge and oil pipelines, prevent the design of a system to collect the water at a single pond, a portion of the stormwater will be allowed to drain directly and the pond will be over regulated to ensure that the total peak flows leaving the property do not exceed predevelopment conditions. This will be referred to as scenario 2.

3.2 Stormwater Facility

The pond has been sized using the HCE-HMS model for both scenarios. Under either scenario, the live storage volume required is 9,000 m3. This volume represents the volume available between the normal water surface and the maximum water level. It would have water in it for about 96 hours after a 1:100 year storm.

The slopes should above the normal water line should 6H:1V to allow for safety and easy maintenance. This same slope should extend 1m below the normal water line. Below that elevation slopes can be increase to 3H:1V to allow for maximum storage. The pond should be 2.5 m deeper than the normal water level in order to maintain good water quality in the pond.

As stated earlier this study has employed the release rate recommendation of the Big Gully Study (4.0 L/s/ha) making the maximum release rate from this facility 0.255 m3/s.

An outlet control with an orifice plate would be provided to limit the release to this maximum rate. If all water can be drained to the pond a 150 mm orifice plate will be required. As shown in Appendix B this would maintain a maximum release rate of 0.23 m3/s.


If all the water cannot be drained to the pond the pond may be controlled at a lower rate such that the maximum flow from the entire subdivision does not exceed 0.255 m3/s. Scenario 2 assumes that those portions south and west of the pipeline corridor cannot be drained to the pond. This area contains approximately 22 hectares. As modeled with HEC-HMS (Appendix B) the maximum uncontrolled release rate from this area is estimated to be 0.17 m3/s. Using a 90 mm orifice plate on the pond’s outlet control the outflow from the pond is limited to 0.7 m3/s, thus resulting in an overall release rate from the pond of 0.24 m3/s.

3.3 Stormwater Quality

In order to provide water quality enhancements, this stormwater facility is designed to be a wet pond with a micro-pool at the inlet locations. At normal water level, the constructed pond will have a typical water depth of 2.5 meters which is based on maintaining water quality. The dead storage of approximately 4000 m3 facilitates the removal of suspended sediment. This storage volume will provide particulate removal that exceeds the performance criteria outlined in Alberta Environment guidelines.

Under Scenario 2

There will direct discharge from up to 22 hectares of land to the receiving channel. A sedimentation pond containing at least 500 m3 of storage should be constructed on the outlet to maintain water quality.

Further all road ditches in the subdivision should be top soiled and seeded to a native grass mixture. These grassed ditches will minimize erosion and trap sediments that do enter.

Good erosion and sedimentation control practices should be maintained during road and house construction.


4 FURTHER REQUIREMENTS The following provides a summary of the requirements for the completion of a Stormwater Management Plan proposed for this development.

1. The outlet downstream of the development as far as the end of the proposed Durness project should be secured through landowner consents. This will probably require the completion or commitment to the completion of the downstream portion of the Durness Project.

2. A final design of the road drainage system should maximize the area that drains to the pond. The sizing of the orifice plate should be finalized once the road drainage design is complete.

3. The final stormwater pond design should be completed in accordance with the parameters provided in this report.

4. The final stormwater plan should provide minimum building grade elevations for all lots and these should be implemented through the building permit stage.

5. The proposed stormwater facility should be licensed through Alberta Environment.

5 CORPORATEAUTHORIZATION

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CORPORATE AUTHORIZATION

This document entitled "Reinhad CouW ReEide iat SuMivlsion Slo/|nwat€rManagement Plan Prcliminary E ry''€€nng Raporl" was prepared by Sameng Inc. forthe account of Reinhart Property Management. The material in it reflecls San€ng's bestjudgmer in light of the information available to it at the time of preparation. Any use whicha third party makes of this report, or any reliance on or decisions made based on it, are theresponsibilities of such parties. Sameng lnc. accepts no responsibility for damages, if any,suffered by any third party es a resu[ of decisions made or aclions based on this report.

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APPENDIX A – FIGURES


Figure A.1 – Natural Drainage Patterns


Figure A.2 – Air Photo


Figure A.3 – Stormwater Facility

Inlet Ditches

Outlet Ditch

Control

Structure

Outlet Pond

Scenario 2


APPENDIX B – HEC HMS RESULTS

Storage (THOU M3)

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Elev (M)

654.8

0

654.9

6

655.1

1

655.2

7

655.4

2

655.5

8

655.7

3

655.8

9

656.0

4

656.2

0

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Flow (M3/S)

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(10

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3)

stormwater master plan nw 21-50-1-4 preliminary ......2.2 design criteria based on the...

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