| Historical notes: | Penrith Weir was built in 1908 and raises the water level 1.5 m above the natural flow, the weir pool extending u/s for 18 km. Penrith Weir was a National Work maintained by the WCIC.
Penrith Weir has suffered both extensive damage and reconstruction in its history. The earliest damage requiring repair work was caused by the 1910 flood. By 1913, the excavations by Emu Gravel created a left abutment weakness and this, combined with floods, resulted in a left bank bypass of the weir. Emu Gravel was operating in the vicinity of the Nepean River prior to the construction of the weir, however subsequent mechanisation improved rates of extraction and deeper holes. The WCIC accepted the extraction activities on the proviso that no removal of material within 2 chains of the river was to occur, it being felt that ‘gravel extraction caused a loss of material at the weir that refilled the extraction holes’ (DPWS 1999). During WWII, the army extracted gravel to within 60 m of the weir.
Flood damage to the weir has been consistent and severe. In 1930 a survey was made of the weir to ascertain the level of damage sustained in floods, these repairs were further delayed by high river (WCIC AR 1930). WCIC AR 1939 notes that repairs were required at Penrith Weir that year, although there is no indication of the level of damage requiring work.
The 1943 floods were particularly bad, with the weir damaged and the grassed left abutment eroded out (trees were uprooted and the natural sand and gravel bed exposed in this flood). In 1949 repairs and extensions were made to the groynes at Penrith Weir at an estimated cost of £255. Due to the high level of the waters after the flood, these works were suspended until the resumption of normal water levels (WCIC AR 1949).
The 1952 flood caused high levels of damage, especially to the left abutment. Ironically the repair works from that flood were interrupted and halted by further flooding (WCIC AR 1952). Repairs were made over the following two years, also interrupted by high river levels, at a cost of approximately £16,500 (WCIC AR 1953 & 1954). Damage to the abutments also occurred in the 1963 flood (highest flow 97,000 cusecs). A gap in the left abutment widened and repairs were undertaken at a cost of £3,500. The 1964 floods (highest flow 388,000 cusecs), further damaged the weir and abutment (WCIC AR 1964). It appears that repairs of the damage caused by the 1964 flood were limited. Interestingly, the 1965 WCIC AR notes that the damage caused by the ‘high flow’ was superficial; however, a 1965 condition report indicates that the crest was intact, but that there were large scour holes and cracked slabs on the left abutment and scour channels through the left bank (DPWS 1999). The left abutment was further damaged in the less severe 1966 floods, suggesting that interim repairs were inadequate. Surveys began in 1966 for extensive repairs to the weir, with plans for the works to be started the following year (WCIC AR 1966).
A major reconstruction program was undertaken in 1969 which included repairs to the main weir wall (the crest was lowered by 9"), d/s gabion protection, a fishway on the left abutment and extensive gabion protection on the left bank u/s of the weir. These repairs were estimated to cost $100,000. They were interrupted by the 1969 flood, which the weir survived moderately intact. The concrete capping on the left bank gravel was removed and this prompted the installation of the gabion cages mentioned above. Repairs were completed in 1970 and it was noted that the left abutment/bank was still considered a weakness (DPWS 1999).
Since these works, the weir has survived all floods moderately intact. During the 1960s, Penrith Weir supplied water to Penrith from pumps installed u/s of the road bridge. There were 14 domestic pumping licences and 20 irrigation licences (DPWS 1999). Questions concerning the expenditure on the weir for the seemingly limited returns, prompted the suggestion that these costs might be borne by other parties. By the late 1960s the then Water Board was prepared to pay 50% of maintenance and repair costs. Recreational use of the weir included the annual "Head of the River" boat race.
A new fishway was constructed on the right abutment in 1989, the third in this position. It is complemented by a ‘small spillway structure that provides an attraction flow to the fishway inlet’ (DPWS 1999).
Penrith Weir is listed on Penrith LEP (a listing transferred to the State Heritage Inventory). It is listed for it’s significance in demonstrating the development of services within the township of Penrith during the early 20th Century (Fox and Associates 1987, NR2).
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