MEMO 
 
TO 
Erik VanderSpek, Principal Ranger, Eastern Sector 
FROM 
John Duggan 
DATE 
4 December 2009 
FILE NUMBER 
PK/01/01/07 
FOR YOUR INFORMATION 
Birchville Dam safety surveillance 
General 
Birchville Dam is a “small dam”, as it holds less than 20,000 m³ of water (not a “large dam” as 
defined by section 7 of the Building Act 2004).   
Regular monitoring and maintenance is required on small dams to ensure there is a low probability 
of failure.  The following recommended dam safety surveillance of Birchville Dam is based on the 
NZSOLD publications Guidelines on Inspecting Small Dams (copy attached) and New Zealand Dam 
Safety Guidelines.   
Inspections 
Routine visual inspections are a key element for the safe operation of any dam.  In general, small 
dams should receive a detailed inspection immediately after each significant flood and earthquake, 
and not less than once a year.   
Proposed inspection regime 
Period Inspection 
by 
After significant event and not less than annually 
Greater  Wellington  Regional  Council  Park  Ranger  or 
Engineering and Projects Engineering Technician 
Five years 
Dam engineer (Consultant) 
 
Generally, “small dams” do not require a comprehensive safety review or inspection by a recognised 
dam engineer until a potential issue is identified.  However, an inspection every five years by a 
recognised dam engineer is recommended for Birchville Dam because:   
  The dam is over 70 years old 
  The dam is a large structure, with a height of approximately 15 m 
  It holds nearly 20,000 m³ of water   
BIRCHVILLE DAM SAFETY SURVEILLANCE [721182]#721182 
 
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  Failure of the dam would have a significant environmental impact 
Attached is a proposed inspection checklist that should be used to record the regular inspections of 
the dam.   
An engineering technician in the Engineering and Projects Team is available to carry out the annual 
inspections if required.   
Previous reports indicate that the dam sluice valve is regularly exercised to ensure continued 
operation of this valve.  I recommend that valve exercising continues and that it be incorporated 
with the annual dam inspection.   
Previous safety review 
The Birchville Dam was last inspected by a dam engineer on 26 May 2006.  The result of this 
inspection by Damwatch Services Ltd is presented in their report held on file PK/01/01/07 
(Powerdocs #358141).   
Proposed new file 
Current correspondence on the Birchville Dam is held on file PK/10/01/07 and PK/08/01/10.  To 
allow easy identification and retrieval of all documents related to the Birchville Dam, I recommend 
that a new file be opened - PK/08/01/14 - with the title Birchville Dam.  Relevant documents in 
existing files should be transferred to this new file.   
John Duggan 
Team Leader Engineering and Projects 
Water Supply 
 
BIRCHVILLE DAM SAFETY SURVEILLANCE [721182] 
 
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