Shifting Sands, Winds, Waves and Waterbodies
left: Wildevoelvlei and south end of Noordhoek Beach as seen from Rooikrans (April 2009) right: Noordhoek Beach as seen from Noordhoek Amphitheatre (Aug 2009)
Note: the given coordinates are for a good sized parking area on the north side of the road approximately 120m east of the required viewpoint which is located @ S34 05.753 S18 21.483 and has its own limited parking space on the south side of the road. Parking on the north side will enable you to approach from, turn around and return to the Noordhoek side if coming from there, and if approaching from the Hout Bay side will enable you to park near to GZ when the viewpoint parking is full - which is often the case.
To Claim the Cache:
- From the viewpoint, observe the current state of the beach and associated water bodies. Given the orientation of the beach and considering current rainfall, wind and wave strength & direction, describe what changes you consider the beach is likely to be undergoing in these conditions.
- Looking at the beach in relation to the adjacent mountains and sandy deposits in Fish Hoek Valley, describe how was you think the sand on the beach was formed, where it most likely came from how it got there?
- Note the position of the wreck of the Kakapo and describe how you think it could be used as a reference point for changes in the beach & shoreline?
- Observe the position of the water treatment plant in relation to the Wildevoelvlei at the south end of the beach (you may need to use binoculars to assist you). Noting this and the appearance/density of nearby vegetation, describe two effects of the discharge of the treated sewage water from the plant.
- Observe the location of sandy deposits in the Fish Hoek valley to the east and describe what beach-related process has been prevented by the various developments in the valley?
Although not required to claim the cache, kindly consider posting a photo of the whole beach & wetland area with your cache log – this will enable comparison of its changing appearance throughout the year.
Note: Please do not publish your answers with your log - send them to my email address or use Personal Message in my profile
Cache Background
On the western side of the Cape Peninsula is the Noordhoek/Wildvoelvlei area which is situated in a low-lying flat-bottomed valley flanked by mountains to the north and south, a low sandy ridge to the east & the Atlantic Ocean to the west.
The central part of the valley has a number of shallow (previously) seasonal vleis or pans with 3 main water bodies:
a) Noordhoek Saltpan: now a permanent shallow lake dredged to a maximum 2m depth to create a canal estate housing development
b) The two Wildevoelvlei which now contain water permanently due to treated nutrient-rich sewage effluent discharge into the upper pan from the nearby sewage works
These are all interconnected via the high water table which exists throughout the entire Noordhoek/Kommetjie basin floor.
The substrate of the valley floor is mainly deep quartzitic sand. The high water table is maintained by one permanent stream (Goeiehoop - draining the Noordhoek amphitheatre) and numerous other seasonal streams which drain the other surrounding mountain slopes. During periods of prolonged rainfall the lower parts of the basin are flooded and the vleis and pans can become interconnected.
The water eventually drains by surface flow and sub-surface seepage into two overwash lagoons situated along the beach. These lagoons which lie in two extended back-beach slacks to the north and south of a central hummock dune area, also receive sea-water from storm waves washing over the beach berm during high spring-tides. They often dry out completely during the summer.
Left: This October 1984 photo shows the two full backwater lagoons. Brown peat-stained water from Papkuilsvlei is flowing out to sea in the central beach area – a rare phenomenon (taken from Estuaries of the Cape) .
The long sandy beach is prograding, ie. undergoing seaward buildup, in this case by nearshore preferential deposition of sand removed by erosion from neighbouring cliffs, which is thrown up by wave action or moved by longshore drifting or strong prevailing winds. This extremely dynamic beach is also affected by seasonal rainfall in the area and subsequent drainage of this into and from the adjacent vleis/lagoons.
These are the main mechanisms thought to affect the beach dynamics:
- short-term onshore-offshore drift of sand due to fluctuations in incident wave height and period
- seasonal onshore-offshore and longshore sand movement mainly due to incident wave direction
- long-term fluctuations in shoreline position (ie, over 1,000s of years) due to variations in sea-level
- aeolian (wind-related) supply of sand which is mainly from the SE to the NW
The relative magnitude of these processes is not well known but seasonal variations in the waterline position of up to 120m occur. Over the last 2 centuries long-term variations of up to 500m have been recorded.
Geology of the area
(taken from Estuaries of the Cape)
The Fish Hoek/Noordhoek gap follows an east/west fault line which forms a valley 2-5 km wide. In the west it broadens out into a low-lying expanse of recent sediments up to 95m deep overlying weathered kaolinised Cape granite. The mountains surrounding the Noordhoek basin consist of quartzitic sandstone of the Table Mountain Group resting on a base of shale which itself rests on granite.
The lower slopes of the mountains surrounding the basin are made up of thick talus formations of sand and Table Mountain Sandstone boulder scree and are generally stable apart from the driftsand area north west of Fish Hoek.
The locality and nature of the quartzitic sands of the Noordhoek/Kommetjie basin and associated offshore sand deposits suggest that these may have originated in False Bay and been blown through the Fish Hoek gap by the prevailing strong summer southeasterly winds. This mechanism no longers exists as most of the area has been developed, or stabilised by vegetation.
An interesting historical landmark of the area is the wreck of the Kakapo, a steamship which ran aground at the southern end of Noordhoek Beach on 25 May 1900 (and is the location of the Mysterious Mishap cache GC1PVKP). The wreck serves as a useful reference point for the changes in the beach profile and shoreline.
Additional Information (of background interest but not needed for the cache):
Poor soil and marshy land make most of the western valley floor unsuitable for development or intensive farming - so there was little interest in the area during early colonization of the Cape Peninsula. Wildevoelvlei means wild-fowl lakes and large numbers of these birds frequent these water bodies which are situated on the farm Imhoff’s Gift. This was originally called Slangkop (Snake Head) when first granted to a Christina Diemer in 1743. Noordhoek (North Glen) lying below Chapman’s Peak, and Chapman’s Bay which extends from Kommetjie to Chapman’s Point are named by John Chapman, a master’s mate who was sent ashore to look for water and an anchorage on 29 July 1607 by the Captain of the English ship Consort which had anchored off the coast.
Use of the Wildevoelvlei/Noordhoek wetlands has been limited to sporadic cash-crop cultivation and some dairy farming in the more fertile areas around the perimeter – which still takes place mainly on the northern and eastern sides of the valley near Noordhoek and Sun Valley.
In places this porphyritic granite under the surface of the valley has been decomposed by weathering into high-grade kaolin which has in the past been exploited at two sites. This eventually ceased due to increasing environmental concerns.
The Noordhoek Saltpan was once used for salt production and, before the pan was dredged to make canals for the new housing development, it was used during the dry months of the year as an unofficial motor racing track!
Glossary:
- Berm: a narrow shelf, path or ledge typically at the top or bottom of a slope
- Nearshore: extending from or occurring along a shore
- Pan: shallow basin or depression in the earth, often containing mud or water.
- Porphyritic: a texture of igneous rocks with a large difference between the size of the tiny matrix crystals and other much larger crystals (phenocrysts)
- Slack: valley or trough between dunes
- Substrate: an underlying layer
- Talus: A sloping mass of rock debris at the base of a cliff
- Vlei: shallow seasonal or intermittent lake (Afrikaans)
Reference:
Estuaries of the Cape, Part II Synopses of Available Information of Individual Systems, Report #27: Wildevoelvlei/Noordhoek (CW28)by TJE Heinecken, Estuarine & Coastal Research Unit, National Research Institute for Oceanlogy, Council for Scientific and Industrial Research, Stellenbosch, South Africa (1986) – available online here
This was used as the primary source of information for the cache.
To Reach the Cache Viewpoint:
Park @ the given coordinates S34 5.716 E18 21.560 in the parking area on the north side of Chapman’s Peak Drive.
Cross the road carefully and proceed a few 100m west along the narrow 'pavement' to the viewpoint bench at S34 5.751 E18 21.843.
Note: If approaching from the Hout Bay side and spot a space at the small parking area at the viewpoint, you can carefully pull in and park there at GZ.
If you decide to investigate the beach area more closely, an access path starting approx 170m further west of here @ S34 5.757 E18 21.373 will take you down through the milkwood forest (passing Paddawan’s Amongst Milkwoods cache GC22TMA en route) to the north end of the beach.
For a closer look @ the Wildevoelvlei area take the turn-off the Kommetjie Rd into Imhoff's Gift residential area @ S34 8.399 E18 21.441 and head for the trail-head near S34 8.235 E18 21.361 off Harrier Close. There are a number of trails which head either along the lakes or through the wetlands towards the coastal tidal pan. However, please be aware that several people have been mugged in the more remote parts of Noordhoek Beach.
If you are very keen, reasonably fit and want a great overview of the southern end of the beach, you could consider hiking to the rarely visited Rooikrans cache GC1PVY0 which takes you to a super viewpoint.
Congratulations to Zambesiboy on his second Earthcache FTF!!