7. Comparing the options
Keeping you informed and inviting your views on the Ponds Project
One way to compare the options with each other, and with the existing situation, is by looking at the
volumes of floodwater that can be temporarily stored in the larger ponds on each chain.
Another comparison is to look at the trade-offs between options, in terms of the impacts of the works downstream of the
increased flood storage areas. These effects are also shown in the options flow chart on board 6. The diagrams below show the
differences in the volumes of floodwater temporarily stored by each option for each chain of ponds. The storage volumes are
estimated using real survey data and maps.
Highgate chain diagrams show:
Hampstead chain diagrams show:
In the existing situation, the temporary storage is generally low. This will mean
that in extreme rainfall and major storms high volumes of water will overflow the
dam in an uncontrolled way.
In the existing situation, the temporary storage is generally low with no storage of
floodwater in the Catchpit Area. This will mean in extreme rainfall floodwater will
flow straight into the Mixed Bathing Pond.
Raising the dams at Model Boating Pond, Men’s Bathing Pond and Highgate No.
1 Pond will increase the amount of water that can be stored at each pond. This
in combination with new open channels around each dam will prevent floodwater
flowing over the dams and will control the release of water more safely.
By constructing a new dam at Catchpit and raising the dams at Mixed Bathing and
Hampstead No. 2 Ponds will result in a significant overall increase in the volume of
floodwater temporally stored for both options.
There is more water stored at Model Boating Pond for option 6 as the result of a
2.5m high dam, which means that the wall at Men’s Bathing Pond can be half a
metre less than in option 4.
Scale
Key
For the Mixed Bathing and Hampstead No. 2 Ponds, option P will store twice the
volume of floodwater than option M. The overall effect of extra storage in option P
means there is less flow to deal with at Hampstead No. 2 Pond and less impact on
the plane trees, with one less tree being lost than in option M.
Key
Volume of water flowing through existing overflow pipes
40,000m
Volume of water flowing through existing overflow pipes
Volume of flood water temporarily stored in ponds
20,000m3
Volume of flood water temporarily stored in ponds
3
Permanent volume of water stored in ponds
0m3
Model Boating Pond
4,921
56,585
71,857
Mens’ Bathing Pond
35,500
Option 4
35,500
Option 6
17,632
17,632
12,812
12,812
97
97
Option M
Option P
0
42
Existing
0m3
Catchpit
10,363
35,500
10,000m3
Permanent volume of water stored in ponds
12,590
8,717
20,000m
3
97
Existing
Mixed Bathing Pond
1,353
752
5,597
47,534
10,257
33,435
10,403
42,900
2,777
3,645
42,900
42,900
8,200
Existing
Option 4
Option 6
Highgate No. 1 Pond
43,356
20,028
Existing
8,200
Option M
22,300
Option 4
8,200
Option P
4,267
5,673
3,312
5,673
11,307
20,200
20,200
20,200
43,356
18,549
22,300
5,032
22,731
11,132
Hampstead No. 2 Pond
20,294
18,112
Existing
7,838
22,300
Option 6
Existing
Option M
Option P
Scale