Storm Water - Lex Toth

                                                                                  Callaghan & Toth

1.        INTRODUCTION

The site subject to this report is at No.10 Opal Street Cooroy. One existing house on the lot
is to be added to by a new dwelling to the rear.

The stormwater management assessment undertaken in this project considers the increase
in impervious area of the lot due to the proposed additional building and measures which
can be incorporated into the design to attenuate the resultant increase in runoff back to
predevelopment levels.

The existing dwelling catchment drains to Opal Street.

The new dwelling site currently drains to Opal Lane as shown on Figure 1.1. the proposed
new drainage system will replicate the existing catchment split.


1.1       Response to Conditions of Approval

TABLE 1.1: Response to Information Request
NUMBER CONDITION                                                          RESPONSE
7a           Detail of proposed tank (location, dimensions, level)        Details shown on Figure
                                                                          1.1
7b           Detail of proposed drainage system (pipe sizes and           Details shown on Figure
             grades)                                                      1.1
7c           Existing and proposed surface levels to demonstrate that     Details shown on Figure
             suitable clearances can be achieved                          1.1
7d           Comment regarding the capacity of the existing drainage      Refer Section 4.2 of this
             system in Opal Street to be achieved                         report
7e           Indications of the various catchment areas within the site   Refer Section 3 of this
             and certification that states if the development is          report
             constructed in accordance with the design there will be no
             worsening of drainage conditions on adjoining properties,
             Opal Street and Opal Lane.


2.        DESCRIPTION

The site is on a 1,009 m2 parcel of land which has frontage to both Opal Street and Opal
Lane. There is an existing underground drainage system with a channel in Opal Street. Opal
Lane road has recently been extended past this site to serve a new development at 8 Opal
Lane.


3.        FLOODING

The existing house drains toward Opal Street. The downpipes discharge into an existing
gully pit in Opal Street.
No.8 Opal Street has an overland flow path along the west boundary which is designed to
take the stormwater overland flow from sag in Opal Street.
The runoff from the existing half of the property currently drains to a low point at the south
west corner of No. 10 Opal Lane. The plan figure 1.1 shows the new development will
maintain this flow path and therefore have no effect on the neighbouring property.


Erthart                              1905 SWMP_Rev0.doc                              April 2019   4
1905