False Bay
False Bay | |
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Valsbaai ( Southern Atlantic Ocean | |
Basin countries | South Africa |
False Bay (
False Bay is at the extreme western end of the inshore
False Bay also contains
Description and location
The western side is bordered by the
In plan the bay is approximately square with rather wobbly edges, being roughly the same extent from north to south as east to west (30 km), with the entire southern side open to the ocean. The area of False Bay has been measured at about 1,090 km2 (420 sq mi), and the volume is approximately 45 km3 (11 cu mi) (average depth about 40 m). The land perimeter has been measured at 116 km, from a 1:50,000 scale map.[2][1]
The eastern and western shores of the bay are very rocky and even mountainous; in places large cliffs plunge into the water. Notable peaks associated with the bay include Koeëlberg (1,289 m (4,229 ft)), which rises from the water itself forming the highest point of the Kogelberg, as well as Somerset Sneeukop (1590m / 5217 feet) and Wemmershoek Peak (1,788 m (5,866 ft)) which are clearly visible across the bay. Some of the highest peaks visible across False Bay include Du Toits Peak near Paarl (1,995 m (6,545 ft)), Klein Winterhoek Peak near Tulbagh (1,995 m (6,545 ft)), Mostertshoek Peak at the Western extreme of the Michell's Pass (2,008 m (6,588 ft)) and Groot Winterhoek Peak North of Tulbagh (2,077 m (6,814 ft)). The northern shore, is defined by a very long, curving, sandy beach. This sandy, northern perimeter of the bay is the southern edge of the area known as the Cape Flats. The bay is 30 km wide at its widest point.[3]
Suburbs of Cape Town stretch right across the Cape Flats from Simon's Town halfway down the Cape Peninsula to the north-eastern corner at Gordon's Bay. There are also two small towns of the Overberg region on the east coast of the bay, Rooiels and Pringle Bay.
Coastal landmarks
Coastal landmarks visible from offshore in False Bay, listed clockwise from Cape Point to Cape Hangklip:[1]
- Cape Point, 34°21′26″S 18°29′51″E / 34.35722°S 18.49750°E, the south-westernmost point of the bay, marked by the current lighthouse and the original lighthouse,
- Vasco da Gama Peak (266m), 34°20′41.07″S 18°28′29.32″E / 34.3447417°S 18.4748111°E, the highest point nearest the mouth of the bay on the Cape Peninsula,
- Rooikrans, 34°20.456′S 18°28.407′E / 34.340933°S 18.473450°E, A cliff area with a small sea cave,
- Matrooskop (109m), 34°19.576′S 18°27.834′E / 34.326267°S 18.463900°E, a small local peak inshore of Buffels Bay,
- Buffels Bay, 34°19.123′S 18°27.650′E / 34.318717°S 18.460833°E, a small bay on the west side of False Bay, with a small craft slipway,
- Bordjiesrif, 34°18.876′S 18°27.782′E / 34.314600°S 18.463033°E, a small, low sandstone promontory on the north side of Buffels Bay,
- Paulsberg (369m), 34°17.635′S 18°27.808′E / 34.293917°S 18.463467°E
- Judas Peak (319m), 34°16.7′S 18°28.3′E / 34.2783°S 18.4717°E,[1] the peak above the cliffs to the immediate south of Smitswinkel Bay,
- Batsata Rock, 34°16.603′S 18°28.836′E / 34.276717°S 18.480600°E, an exposed inshore granite rock below Judas Peak near the northern boundary of the Paulsberg restricted zone, and the southern limit of Smitswinkel Bay,
- Smitswinkel Bay, 34°16.007′S 18°28.261′E / 34.266783°S 18.471017°E, a small bay on the west side of False Bay, with a few coastal houses,
- Baboon Rock, 34°15.466′S 18°28.339′E / 34.257767°S 18.472317°E, a landmark indicating the southern extent of the Castle Rock restricted area,
- Partridge Point, 34°15.343′S 18°28.606′E / 34.255717°S 18.476767°E, a granite corestone promontory with several large exposed inshore rocks extending about a hundred metres into the bay on the north side of Smitswinkel Bay,
- Finlay's Point, 34°14′56.9″S 18°28′36.5″E / 34.249139°S 18.476806°E, a smaller granite corestone promontory north of Partridge Point,
- Castle Rocks, 34°14.362′S 18°28.661′E / 34.239367°S 18.477683°E, a larger granite corestone promontory, comprising a massive and fairly high outcrop at the end of a small, low isthmus, with several large inshore exposed rocks south of Miller's Point,
- Bakoven Rock, 34°14.040′S 18°29.012′E / 34.234000°S 18.483533°E, an exposed inshore granite rock between Castle Rocks and Miller's Point, near the northern extent of the Castle Rocks restricted area,
- Rumbly Bay, 34°14.020′S 18°28.489′E / 34.233667°S 18.474817°E, a small cove with a small craft slipway on the south side of Miller's Point,
- Millers Point, 34°13.932′S 18°28.587′E / 34.232200°S 18.476450°E, a fairly large but low granite corestone promontory, with a small craft slipway on the northwest side, and several exposed and drying rocks extending to seaward,
- Spaniard Rock, 34°13.030′S 18°28.017′E / 34.217167°S 18.466950°E, an inshore exposed granite rock off Rocklands Point,
- Rocklands Point, 34°12.964′S 18°27.921′E / 34.216067°S 18.465350°E, a minor granite promontory north of Miller's Point,
- Swartkop (679m), 34°12.943′S 18°27.025′E / 34.215717°S 18.450417°E, the highest point on the Southern Peninsula,
- Simonsberg (548m), 34°12.299′S 18°26.304′E / 34.204983°S 18.438400°E, the peak above Simon's Town,
- Oatlands Point, 34°12.067′S 18°27.395′E / 34.201117°S 18.456583°E, a minor granite promontory with a large inshore exposed rock and a shoreline navigation beacon,
- Fishermans Beach, , a short, sandy beach north of Oatlands Point,
- Froggy Pond, 34°12.219′S 18°27.418′E / 34.203650°S 18.456967°E, a small cove with a small sandy beach north of Fishermans Beach separated by a low rocky promontory,
- Windmill Beach, 34°12.067′S 18°27.395′E / 34.201117°S 18.456583°E, a small sandy beach partly enclosed by massive granite boulders, with two small coves,
- Noah's Ark rock, 34°11.533′S 18°27.231′E / 34.192217°S 18.453850°E, a conspicuous inshore exposed rock at the mouth of Simon's Bay,
- Simon's Bay, 34°11.073′S 18°25.945′E / 34.184550°S 18.432417°E, the largest bay on the west side of False Bay, very well protected from the prevailing south westerly swell, but fairly exposed to wind and waves from the south-east,
- Boulders Beach, Seaforth, 34°11.833′S 18°27.082′E / 34.197217°S 18.451367°E, a sandy beach between large scattered granite boulders,
- Simon's Town Naval Base harbour, 34°11.317′S 18°26.283′E / 34.188617°S 18.438050°E, a man-made harbour with breakwater and sea-walls enclosing the naval dockyard,
- False Bay Yacht Club moorings, 34°11.427′S 18°26.015′E / 34.190450°S 18.433583°E, a floating marina protected from the south-easterly wind and waves by the naval harbour, with somewhat less protected open moorings further into the bay,
- Long Beach, 34°11.236′S 18°25.579′E / 34.187267°S 18.426317°E, a sandy beach on the west side of Simon's Bay, usually in the lee of the harbour for south easterly winds,
- Roman Rock, 34°10.877′S 18°27.606′E / 34.181283°S 18.460100°E, an exposed rock in Simon's Bay with a lighthouse on it,
- Mackerel Bay, 34°10.302′S 18°25.761′E / 34.171700°S 18.429350°E, a small sandy beach north of Simon's Town,
- Glencairn, 34°9′48″S 18°25′47″E / 34.16333°S 18.42972°E, a small residential suburb in a valley north of Simon's Town, with a beach in Elsebaai,
- Elsebaai, 34°09.593′S 18°25.921′E / 34.159883°S 18.432017°E, a small bay in the north part of Simon's Bay,
- Glencairn quarry, 34°09′13″S 18°26′11″E / 34.15366°S 18.43629°E,[4] a conspicuous excavation in the side of Else Peak,
- Else Peak (303m), 34°09.000′S 18°26.113′E / 34.150000°S 18.435217°E, a small peak between Simon's Town and Fish Hoek,
- Fish Hoek bay, 34°08′15″S 18°26′01″E / 34.13745°S 18.43374°E, the northernmost minor bay of the west side of False Bay with a sandy beach open to the sea,
- Sunny Cove, 34°08.661′S 18°26.239′E / 34.144350°S 18.437317°E, the rocky sandstone coastline on the south side of Fish Hoek bay,
- Fish Hoek beach, 34°08.160′S 18°26.148′E / 34.136000°S 18.435800°E, a sandy beach on the east side of the Fish Hoek–Noordhoek gap, a low-lying break in the mountain range of the peninsula between False Bay and the Atlantic coast.
- Trappieskop, 34°07.668′S 18°26.414′E / 34.127800°S 18.440233°E, the hill above Kalk Bay,
- Kalk Bay harbour, 34°07.698′S 18°26.986′E / 34.128300°S 18.449767°E, a small commercial fishing harbour in Kalk bay, completely enclosing the tiny sandy beach,
- St James, 34°7′8″S 18°27′33″E / 34.11889°S 18.45917°E, the suburb to the north of Kalk Bay,
- Kalkbaaiberg (517m), 34°06.737′S 18°26.382′E / 34.112283°S 18.439700°E, the peak above Kalk Bay
- Muizenberg (509m), 34°06.006′S 18°27.556′E / 34.100100°S 18.459267°E, the peak to the west of Muizenberg suburb, and the northernmost peak directly overlooking the west side of False Bay,
- Muizenberg beach (Sunrise Beach), 34°06′04″S 18°29′22″E / 34.10120°S 18.48948°E-->, a long sandy beach along the low-lying northwestern coast of False Bay,
- Kapteinsklip, 34°04.726′S 18°37.249′E / 34.078767°S 18.620817°E, a low rocky promontory between Muizenberg and Strandfontein beaches,
- Strandfontein, 34°05.326′S 18°33.204′E / 34.088767°S 18.553400°E,
- Wolfgat Nature Reserve, 34°04′11″S 18°38′54″E / 34.0697°S 18.6482°E, a small coastal nature reserve on the north coast of the bay,
- Swartklip, 34°04.477′S 18°41.118′E / 34.074617°S 18.685300°E,
- Monwabisi, 34°04′22″S 18°41′10″E / 34.072853°S 18.686209°E,[4] a resort area on the north coast of the bay,
- Macassar Beach, 34°04′35″S 18°45′08″E / 34.07643°S 18.75224°E,[4] a long stretch of sand beach on the north coast of the bay,
- Eerste River mouth, 34°04.873′S 18°45.887′E / 34.081217°S 18.764783°E, the mouth of the largest river crossing th Cape Flats,
- Helderberg Marine Protected Area, 34°05′S 18°47′E / 34.083°S 18.783°E, a small coastal marine protected area between the mouths of the Eerste and Lourens rivers,
- Lourens River mouth, 34°06.005′S 18°48.706′E / 34.100083°S 18.811767°E, the mouth of the river flowing through Somerset West and Strand,
- Strand Beach, 34°06′20″S 18°49′04″E / 34.10554°S 18.81776°E,[4] a sandy shoreline along the coast of the suburb, becoming rocky to the east,
- Harbour Island marina, 34°09.097′S 18°51.356′E / 34.151617°S 18.855933°E, a small craft harbour development on the north-eastern coast of the bay,
- Gordon's Bay beach, 34°09.499′S 18°52.070′E / 34.158317°S 18.867833°E, a small sandy beach in the north-eastern corner of the bay,
- Gordon's Bay Harbour, 34°09.801′S 18°51.504′E / 34.163350°S 18.858400°E, a small fishing harbour and marina,
- Steenbras River mouth, 34°11.671′S 18°49.194′E / 34.194517°S 18.819900°E, mouth of a river with catchment to the east of the Hottentots Holland range,
- Boskloof Peak (648m), 34°12′15.12″S 18°50′20.04″E / 34.2042000°S 18.8389000°E, mountain peak south of the Steenbras River mouth,
- Boskloof Point, 34°13.028′S 18°49.777′E / 34.217133°S 18.829617°E, promontory south of the Steenbras River mouth,
- Kogelbaai, 34°14′02″S 18°50′56″E / 34.23397°S 18.84900°E,[4] a fairly long sandy beach on the east coast of the bay,
- Kogelberg, 34°13.880′S 18°53.253′E / 34.231333°S 18.887550°E, a mountain peak above Kogelbaai,
- Rooielsberg (638m), 34°16.960′S 18°50.112′E / 34.282667°S 18.835200°E, a peak above the point to the north of Rooi-Els,
- Rooi-Els River mouth, 34°17.848′S 18°49.20′E / 34.297467°S 18.82000°E, the mouth of the Rooi-Els river at a small sandy beach in Rooi-Els bay,
- The Point (Rooi-Els), 34°17′51″S 18°48′50″E / 34.29750°S 18.81389°E,
- Klein Hangklip (309m), 34°18′26″S 18°49′19″E / 34.30722°S 18.82194°E, a small peak overlooking Rooi-Els,
- Rooi-Els, 34°18′05″S 18°48′59″E / 34.30139°S 18.81639°E, a small coastal residential area in the Overbergdistrict,
- Pringle Bay, 34°20′31″S 18°49′16″E / 34.34194°S 18.82111°E, A small, shallow bay on the south-east side of False Bay, which has a small sandy beach on the east and a rocky coastline to the south, with a small residential town along the shore,
- Buffels River mouth, 34°20′20″S 18°40′47″E / 34.33889°S 18.67972°E, the mouth of a small river, draining into Pringle Bay,
- Die Punt (Pringle Bay), 34°20′55″S 18°48′38″E / 34.34861°S 18.81056°E, The point to the south of Pringle Bay,
- Pringle Peak (159m), 34°21′4.17″S 18°49′18.37″E / 34.3511583°S 18.8217694°E, Peak at Pringle Bay,
- Hangklip (455m), 34°21.919′S 18°49.700′E / 34.365317°S 18.828333°E, peak at the south eastern extreme of False Bay, with near vertical profile on the south side,
- Cape Hangklip, 34°21′13″S 18°49′39″E / 34.35361°S 18.82750°E, a low promontory extending southwards below Hangklip Peak,
Bottom morphology
The bottom morphology of False Bay is generally smooth and fairly shallow, sloping gently downwards at about 3 m per km from north to south, so that the depth at the centre of the mouth is about 80 m. The bottom is covered with sediment which ranges from very coarse to very fine, with most of the fine sediment and mud in the centre of the bay. The main exception is a long ridge of sedimentary rock that extends in a southward direction from off the Strand, to approximately level with the mouth of the Steenbras River. The southern tip of this ridge is known as Steenbras Deep.[2][1]
There is one true island in the bay, Seal Island, a barren and stony outcrop of granite about 200 m long and with an area of about 2 ha. It is about 6 km south of Strandfontein and is less than 10 m above sea level at its highest point. There are also a number of small rocky islets which extend above the high water mark, and other rocks and shoals which approach the surface. The largest of these, and the most significant navigational hazard in the bay, is Whittle Rock, a large outcrop of granite about halfway into the bay and a quarter of the way across from the Cape Peninsula (34°14.846′S 18°33.714′E / 34.247433°S 18.561900°E), which is about a kilometre in diameter and rises from a fairly flat sand bottom at about 40 m to within 4 m of the surface. There are smaller outlying granite reefs scattered to the south, east, and west of Whittle Rock, and more smaller granite reefs to the northwest. Most of these reefs on the western side of the bay are granite of the Peninsula pluton, but east of Seal Island they are generally sandstone, either of the Table Mountain series, or of the underlying Tygerberg formation.[2][5][1] Whittle Rock reef can refract large south easterly storm waves, increasing their size in the vicinity of Kalk Bay harbour.[6]
Other shoal areas include the granite reefs at Roman Rock in Simon's Bay, hard sedimentary or metamorphic rock at York shoal and hard sandstone at East shoal, and several isolated granite outcrops which are too deep to be navigational hazards in the western part of the bay.[1] The palaeo-drainage of the bay is split between the western side of the bay and the eastern side by the relatively durable contact zone between the Peninsula granite and the Tygerberg sediments, with deep valleys cut into the bedrock during the glacial maximum, which have since been filled with sediments. The drainage of the west side passed to the west of Seal Island, Whittle Rock and Rocky Bank. The east side was drained by a valley between Seal Island and East Shoal, and another valley to the east of Steenbras Ridge, which joined east of Rocky bank and exit the bay between Rocky bank and Hangklip Ridge.[7]: Ch2
Outside the bay, but influencing the wave patterns in it, is Rocky Bank, an extensive area of relatively flat sandstone reef between 20 and 30 m depth on the top, sloping down on all sides, but mostly to the south and east, where the depth can exceed 100 m.[2][1] A long underwater sandstone ridge sweeps across the eastern side of the mouth from Cape Hangklip towards the southwest, that is believed to affect water circulation in the bay. On the west side, a relatively shallow area of granite reef extends beyond the Cape Peninsula, with one major navigational hazard at Bellows Rock and a lesser one somewhat closer inshore at Anvil Rock.[1][6]
Bathymetry
The bathymetry of False Bay differs in character from the west side of the Cape Peninsula. The west coast seabed tends to slope down more steeply than in False Bay, and although the close inshore waters are also shallow, the 100 m contour is mostly within about 10 km of the west coast, while the entire False Bay is shallower than about 90 m.
Geology
The three main rock formations are the late-
At times the sea covered the Cape Flats and Noordhoek valley and the Cape Peninsula was then a group of islands, and False Bay and the Cape Flats a strait. During glacial periods the sea level dropped to expose the bottom of False Bay to weathering and erosion, the last major regression leaving the entire bottom of False Bay exposed. During this period an extensive system of dunes was formed on the sandy floor of False Bay. At this time the drainage outlets lay between Rocky Bank and Cape Point to the west, and between Rocky Bank and Hangklip Ridge to the east.[5][7]: Ch2
Waves, tides, water circulation and temperature
Waves along the north coast of the bay between
Northward propagating long period waves are focused in the northeast and northwest parts of False Bay by refraction effects over the shoal waters of Rocky Bank in the mouth of the bay, with measured heights of waves in the area between Steenbras mouth and Kogelbaai being up to twice the height of the waves in the Muizenberg to Strandfontein region for the prevailing southwesterly open ocean swell.[9] The focusing effect is mostly on swells with a period of 13 seconds or more, and a direction between 210° and 245° true.[10] The smaller and shallower reef at Whittle Rock towards the west side of the bay has a similar but lesser effect, and can focus longer period south-easterly waves on Kalk Bay. This is unusual and associated with a cut-off low pressure system causing the south-easterly winds to blow for an unusually long time over enough fetch to develop a sea sufficiently for it to be refracted by the shoal area.[11]: App3 Wave height of southwesterly swells decreases from west to east along the north coast of False Bay from around Macassar to Gordon's Bay due to the effects of refraction and friction of the wave base on larger areas of offshore reef before reaching the shoreline.[11]: 16
The circulation patterns of False Bay are variable over time, with seasonal and longer term cycles. There are cold-water upwelling events associated with south-easterly winds in summer, and periodic intrusions of warm water eddies from the Agulhas Current of the south coast, both of which contribute to the biodiversity.[6]
Four main surface circulation patterns have been observed in False Bay. Wind is the dominant forcing influence on surface circulation, with tidal and inertial currents of secondary importance, mainly when the winds are weak.[13] Gordon's Bay is in the wind shadow of the Hottentots-Holland Mountains for south easterly winds, and this causes a semi-permanent anticyclonic eddy and associated anticlockwise gyre, in the opposite direction to the usual cyclonic circulation of the main part of the bay.[6]
A clockwise rotation driven by the south-easterly winds mostly occurs during summer. This circulation is partly set up by west-north-westerly flow south of the bay splitting at Cape Point. The northerly component sets up flow towards the equator on the western shores. South-easterly winds cause this clockwise pattern to dominate. North-westerly winds cause an anti-clockwise circulation, with an eastward current flowing south of the Bay and entering at Cape Hangklip.[13] When there is no strong wind forcing, tidal forcing can occur on the incoming and outgoing tides. A fairly uniform northward flow occurs during flooding tides, and southward during ebbing tides, with bathymetry affecting the flow direction in shallow areas. These currents are most noticeable along the coastline and in the shallow northern parts of the bay between Simon's Town and Gordon's Bay.[13]
In the deeper areas of the mouth of the bay, tidal and inertial currents appear to contribute to the variability of the deeper part of the water column, along with the effects of wind forcing. Wave energy focused by the various shoal areas outside and inside the bay is a driver of nearshore currents, particularly in the northern parts of the bay.[13]
In summer False Bay is thermally stratified, with a vertical temperature variation of 5 to 9˚C between the warmer surface water and cooler depths below 50 m, while in winter the water column is at nearly constant temperature at all depths. The development of a thermocline is strongest around late December and peaks in late summer to early autumn.[14]: 8 In summer the south easterly winds generate a zone of upwelling near Cape Hangklip, where surface water temperatures can be 6 to 7 °C colder than the surrounding areas, and bottom temperatures below 12 °C.[14]: 10
In the summer to early autumn (January–March), cold water upwelling near Cape Hangklip causes a strong surface temperature gradient between the south-western and north-eastern corners of the bay. In winter the surface temperature tends to be much the same everywhere. In the northern sector surface temperature varies a bit more (13 to 22 °C) than in the south (14 to 20 °C) during the year.[6]
Surface temperature variation from year to year is linked to the El Niño–Southern Oscillation. During El Niño years the South Atlantic high is shifted, reducing the south-easterly winds, so upwelling and evaporative cooling are reduced and sea surface temperatures throughout the bay are warmer, while in La Niña years there is more wind and upwelling and consequently lower temperatures. Surface water heating during El Niño increases vertical stratification. The relationship is not linear.[6]
Water density dynamics are mostly temperature dependent, with only weak influences from salinity. The major influence on temperature distribution is wind driven upwelling and advection of cold water, which is most notable north-west of Hangklip, and less marked near Gordon's Bay, due to strong south-easterly winds, with insolation as a secondary effect, mostly in the shallow waters of the northern and north-easterly regions. Waves may have more influence on nearshore temperature than wind. Upwelling outside the bay along the coast east of Hangklip can also supply cold water to the bay[13]
Rivers and drainage
Drainage into False Bay can be considered from four watersheds: The east-flowing streams of the southern Cape Peninsula, the Cape Flats, the Helderberg basin, and the south-westwards drainage of the Hottentots-Holland mountains of the Overberg, extending south as far as Cape Hamgklip.
The eastward draining rivers of the Southern Peninsula are generally fairly short and steep, and some, such as the Silvermine and Elsje rivers, have valley bottom wetlands at the coast.[15]: Ch15 The Buffels River flows from a small spring to its mouth in Buffels Bay, the Klawersvlei River[16] flows northwest from behind the mountains above Miller's Point over the plateau behind Simon's Town, before turning east over the escarpment and a high waterfall, entering the bay near the Simon's Town railway station, the Elsjes River[16] flows from the Red Hill plateau to enter False Bay from the Glencairn valley, and the Silvermine River,[16] originally known as the Esselstein Rivier, drains the valley south of the Steenberg mountains and flows east across the Steenberg Plateau, then south through the Silvermine Valley before crossing the coastal Fish Hoek plain to enter False Bay at Clovelly on the north side of Fish Hoek Bay. Between these short and fairly steep streams, rainwater runoff generally flows directly down the mountainside into the bay.
The Sandvlei catchment drains the east side of the mountains north of Muizenberg and south of the Liesbeek catcment into False Bay:[15]: Ch13 Sandvlei (Zandvlei) is the largest of eight estuaries on the False Bay coastline, with an area of about 155 hectares. It is fed by the Westlake, Keysers and Sand rivers. The Diep River flows from the mountains above Constantia to Little Princessvlei, which is drained by the Sand River, which flows into the northeast of Sandvlei. The Westlake River, also known as the Steenberg or Raapkraal River, originates on the slopes of the Steenberg and flows through the Kirstenhof wetlands into the north west of Sandvlei, and the Keysers River and its tributaris, the Grootbosch, Spaanschemat and Prinseskasteel rivers rise on Constantiaberg. The upper reaches of the Spaanschemat River are known as the Glen Alpine Stream, which originates below Constantia Nek and is joined by the Eagles Nest Stream.
Historically the Cape Flats was partly covered in wetlands, particularly during winter, and retained much of its rainfall. Many of these wetlands have been destroyed by canalisation and infilling to provide residential space. Many of the remaining perennial
The Eerste River and its tributary the Kuils River, drain into False Bay on the north coast, west of the Helderberg basin watershed. They drain part of the Cape Flats, but most of the catchment of the Eerste River is in the Stellenbosch district, between the Helderberg and Stellenbosch Mountains, and the Jonkershoek Valley.[15]: Ch18 [15]: Ch16
The catchment of the Lourens River is in the Helderberg region. It is the largest river of the region. The source is in Diepgat Ravine, in the Hottentots Holland Mountains. It is joined by minor tributaries from Landdroskloof and Sneeukopkloof in its upper reaches, The river flows in a south-westerly direction between the Helderberg and Schapenberg through Somerset West and Strand to a small estuary on the coast of False Bay. Its overall length is about 20 kilometres.[15]: Ch19
The Soete River is a small river that may have originally been part of the Lourens River system, diverting floodwater through an alternative route to the bay.[15]
Sir Lowry's River drains the south side of Schapenberg and west side of the Hottentots Holland south of Schapenberg. It enters the bay in Gordon's Bay.[15]
The Steenbras River catchment is to the east of the Hottentots Holland mountains, and almost all of its water is retained by the upper and lower Steenbras Dams, which are a significant part of the municipal water supply to the City of Cape Town. Steenbras River mouth is south of Gordon's Bay.
The Rooiels River enters False Bay at Rooiels beach. It drains a small catchment area in a nature reserve in the mountains of the southwest of the Overberg district.
Water quality
The nutrient contribution to False Bay surface waters by upwelling appears to be greater than that of terrestrial sources by runoff and groundwater seepage, but pollutants from terrestrial sources can be persistent and can have adverse effects on coastal ecosystems and recreational activities. Mixing with offshore water has a significant effect on surf zone and inshore water quality, but the effects of microbial processes on inshore water quality and the relative contribution of anthropogenic sources of nutrients remains unknown, but likely to be increasing.[6]
History
In pre-colonial times False Bay along with most of the Southern African coast provided sustenance to the Khoisan or Khoekhoen tribe who collected seafood from the shores and deposited the shells in middens along the coast which indicate usage over some 10 000 years.[6] Bartolomeu Dias in 1488 first referred to the bay as "the gulf between the mountains".[17] The name "False Bay" was applied early on (at least three hundred years ago) by sailors who confused the bay with Table Bay to the north. According to Schirmer, the confusion arose because sailors returning from the east (The Dutch East Indies) initially confused Cape Point and Cape Hangklip, which are somewhat similar in form. Hangklip was known to the early Portuguese seafarers as Cabo Falso, or False Cape, and the name of the bay derived from the cape.[17] Commercial fishing was started in the late 17th century soon after settlement by the Dutch.[6]
In 1672 the Dutch warship Goudvinck was stationed at the Cape and was instructed to survey False Bay, but it is not known how much was done before they were recalled. Simon van der Stel, appointed commander of the station in 1679, sailed False Bay in November 1687 on the ship De Noord, took the earliest recorded soundings, and described the islands, reefs and shoreline of the bay. By the end of the 17th century the general bathymetry was known.[18]
The Whittle Rock reef is named after a lieutenant Whittle of the Royal Navy, who surveyed parts of False Bay after HMS Indent was damaged off Miller's Point soon after the first British occupation of the Cape in 1795.[19]
Commercial fishing has been practiced in False Bay since the late 1600s. Over time a range of fishing methods have been prohibited in False Bay. Demersal trawling, purse seining and gillnetting were introduced in the 19th century, but have been stopped as they were depleting stocks, conflicting with other fisheries and users, and damaging the environment. Illegal gillnetting is still a problem.[6]
Penguin eggs were collected until 1968, whaling operations took place until 1975, seals were hunted for fur until 1984, and guano was collected until 1991. All of these activities had a severely detrimental effect on the targeted populations and are now illegal. Commercial abalone diving has been severely restricted as the resource was overfished but illegal exploitation of the resource continues. Recreational abalone extraction has been discontinued.[6]
There have been symposia, in 1968 and 1989, on the socio-ecological importance of False Bay, with reviews of the oceanography and biology of the bay and human impact on it.[6]
Shipwrecks
Over the years, a number of ships have been wrecked in False Bay, due to weather, war, errors in navigation, other accidents, or intentional scuttling. These include:[20]
Shipwrecks:
- Ship Robert, sprang a leak and was beached without loss of life near Gordon's Bay on 12 February 1847. (Cape of Good Hope Almanac, 1852, p105)
- Dutch East India schooner Catwyk aan Rhyn, driven ashore in a gale in Simon's Bay without loss of life on 7 October 1786.[21]
- French frigate Penelope 16 October 1788[21]
- Dutch ship Drietal Handelaars 16 May 1789[21]
- Britush turret steamer SS Clan Stuart ran aground at Glencairn, 21 November 1914[22][23] 34°10.303′S 18°25.842′E / 34.171717°S 18.430700°E
- Waterloo wrecked at Fish Hoek on 25 October 1821[24][25]
- Cockburn wrecked on Muizenberg beach in 1823[26][27]
- French whaler Le Protee wrecked at Strandfontein on 10 January 1839[28]
- Barque Admiral Cockburn wrecked at Muizenberg beach on 27 July 1839[28][29]
- Schooner Felix Vincidor wrecked at Muizenberg beach on 28 July 1841[30]
- Slaving barque Rowvonia wrecked in Simon's Bay on 13 January 1850[31]
- Dutch warship Bata (HNMS Bato?), burned and sank in Simon's Bay in 1803 at34°10.998′S 18°25.560′E / 34.183300°S 18.426000°E
- Portuguese warship Sarpine wrecked near Hottentot's Holland in 1691[32][33]
- Sloop Benjamin lost with all hands at Gordon's Bay on 20 September 1800[34][35]
- Dutch East Indiaman Hollandia Caught fire and sank in Simon's Bay c.1720
- HMS Trident struck Whittle Rock and sank[36]
- British East Indiaman Euphrates struck Whittle Rock and sank[36] in about 1810[37]
- Brig Camille wrecked at Muizenberg beach on 18 October 1816[38]
- Benefactress wrecked at Lourens River mouth, The Strand, in November 1870[39]
- Prussian barque Johanna Wagner wrecked at Zandfontein near Muizenberg on 16 July 1862[40]
- Schooner Nukteris (Nuchteris?) wrecked at Buffels Bay just north of Cape Point on 9 August 1897[41]
- Padang (Padarig?) wrecked in Simon's Bay on 29 June 1828[42][43]
- Parana (Panama?) Wrecked in Simon's Bay on 9 October 1862
- Phoenix wrecked at Phoenix shoal off Boulders Beach, Simon's Town on 19 July 1829[44] at34°11.388′S 18°26.898′E / 34.189800°S 18.448300°E
- Frigate Revolutionnaire wrecked in Simon's Bay on 29 July 1816
- Vrouw Ida Alida wrecked at Muizenberg in 1818[45]
- Zebra wrecked in Simon's Bay on 29 July 1816
- Rex wrecked in the vicinity of Fish Hoek in 1903
- British East Indiaman Colebrooke wrecked south of Steenbras River mouth on 25 August 1778[21]
- English East Indiaman Brunswick wrecked at Long Beach in Simon's Bay at 34°10.880′S 18°25.607′E / 34.181333°S 18.426783°E
Scuttled:
- MV Rockeater scuttled as an artificial reef in Smitswinkel Bay on 15 December 1972 at 34°16.127′S 18°28.890′E / 34.268783°S 18.481500°E
- SAS Pietermaritzburg scuttled as a recreational dive site just north of Millers Point at 34°13.303′S 18°28.465′E / 34.221717°S 18.474417°E
- SAS Good Hope scuttled as an artificial reef in Smitswinkel Bay at 34°16.054′S 18°28.850′E / 34.267567°S 18.480833°E
- SAS Fleur scuttled in central False Bay north of Whittle Rock at 34°10′50″S 18°33′54″E / 34.1805°S 18.5649°E
- SAS Transvaal scuttled as an artificial reef in Smitswinkel Bay at 34°16.005′S 18°28.761′E / 34.266750°S 18.479350°E
- SAS Bloemfontein scuttled in central False Bay at 34°14′39″S 18°39′57″E / 34.2443°S 18.6659°E
- MFV Princess Elizabeth scuttled as an artificial reef in Smitswinkel Bay at 34°16.068′S 18°28.839′E / 34.267800°S 18.480650°E
- MFV Orotava scuttled as an artificial reef in Smitswinkel Bay at 34°15.998′S 18°28.774′E / 34.266633°S 18.479567°E
- Muizenberg Trawler wrecks, ST Bulby and ST Iolite scuttled off Muizenberg at:
- Western trawler wreck: 34°07.006′S 18°31.219′E / 34.116767°S 18.520317°E
- Eastern trawler wreck: 34°06.996′S 18°31.360′E / 34.116600°S 18.522667°E
- ST Godetia scuttled as an air-force training exercise off Macassar at about 34°06′S 18°44′E / 34.1°S 18.73°E,
- SATS General Botha scuttled in central False Bay east of Whittle Rock by gunfire from a battery at Simon's Town at 34°13.679′S 18°38.290′E / 34.227983°S 18.638167°E
Climate
The climate is Mediterranean, with warm, dry summers and cool, damp winters. In winter, gales and storms from the northwest are common and can be ferocious. False Bay is exposed to southeasterly winds in summer and its waters are approximately 6 °C warmer than those of Table Bay, owing to the influence of the warm Agulhas Current. The La Niña phase of the El Niño–Southern Oscillation cycle tends to increase rainfall in this region in the dry season (November to April).[46]
Winds
The winds have a strong influence on the waves and water circulation and through it the sea surface temperature. The wind follows a characteristic pattern, which shifts in latitude with the seasons and follows the Rossby waves as they move eastwards over the southern ocean. A southwesterly wind follows the passage of a cold front as the anticyclone moves east and merges with the South Atlantic High, producing strong south-easterly winds. The high pressure cell moves further over the tip of Africa and splits off the South Atlantic high, with weakening south easterly winds, followed by a coastal low with north-westerly wind before the next cold front, bringing cool, wet westerly wind which passes around Table Mountain and converges as a northerly wind over the bay.[6]
The South Atlantic high shifts latitude with the seasons, following the sun, and this causes a large variation in the wind pattern over the passage of the year. In summer it moves south and the south-easterly winds dominate, and on average are strongest during January and February. During winter the northward shift allows the fronts to extend further north with stronger north-westerly winds and more frequent and heavier rain. The winter winds tend to be strongest in June and are generally northwesterly. The transition periods are April and September.[6] The El Niño–Southern Oscillation (ENSO) affects the winds and rainfall over this region.
Sea surface temperatures off the west and south coasts of South Africa are affected by ENSO via changes in surface wind strength.[47] During El Niño the south-easterly winds driving upwelling are weaker which results in warmer coastal waters than normal, while during La Niña the same winds are stronger and cause colder coastal waters. These effects on the winds are part of large scale influences on the tropical Atlantic and the South Atlantic High-pressure system, and changes to the pattern of westerly winds further south. There are other influences not known to be related to ENSO of similar importance. Some ENSO events do not lead to the expected changes.[47]
Local variations in wind direction and strength are caused by interaction with the mountains on both sides of the bay. South-easterly winds are accelerated northwest of Cape Hangklip, and a distinct wind shadow can develop in the lee of the Kogelberg mountain. Northwesterly winds accelerate over Table Mountain and approach the bay from varying directions depending on the local topography. Temperature differences between land and water can also produce diurnal variations of wind speed and direction, particularly in summer.[6]
Ecology and marine life
False Bay is at the extreme western end of the inshore
There are two marine protected areas in False Bay: The Table Mountain National Park Marine Protected Area (TMNPMPA) lies on both sides of the Cape Peninsula, so is partly in False Bay,[50] and the Helderberg Marine Protected Area is off Macassar on the northern shoreline of the bay.[51]
There are concerns as to the effect the disappearance of great white sharks in False Bay will have on the local ecosystem, as the sharks serve as the main predator of the local population of
Reef ecosystems
Six feeding groups have been identified among the common suprebenthic fish species of False Bay, based on a comparison of diets. These are generalised benthic carnivores. carnivorous benthic browsers, herbivorous benthic grazers, midwater predators on small invertebrates, benthic macro-predators, and predators on small benthic invertebrates. These groups appear to eat mostly reef-dwelling prey, with the small amount of sand-dwelling assumed to be from areas adjacent to the reef. Feeding occurs mostly when water temperatures exceed 13°C. There is some overlap of diet between species, but in most cases each species has a dietary niche of preferred food, which reduces competition for food between the species within the assemblage.[53]
Habitat types
The benthic habitat types listed for False Bay in the National Biodiversity Assessment are:[6]
- Estuaries
- Estuarine shore
- Dissipativesandy coast
- Dissipative-intermediate sandy coast
- Intermediate sandy coast
- Reflectivesandy coast
- Mixed shore
- Boulder shore
- Sheltered rocky coast
- Exposed rocky coast
- Very exposed rocky coast
- Sandy inshore
- Sandy inner shelf
- Hard inshore
- Hard inner shelf
- Hard outer shelf
- Reef
- Island buffer zone, and
- Harbour
Fauna
The marine animals of False Bay are diverse and varied. The more popularly known species which are a tourist draw include white sharks, abalone, African penguins, snoek, yellowtail, and many over-exploited linefish species, west coast rock lobster, and abalone. Besides the resident species and several known migrants, the waters of the MPA are occasionally visited by vagrants carried in by the eddies of the Agulhas Current, which can bring tropical and subtropical specimens normally resident thousands of kilometres away.[54]
- Great white shark
- Cape fur seal
- Cetaceans
- Southern right whale
- Humpback whale
- Bryde's whale
- Pygmy right whale
- Heaviside's dolphin
- Dusky dolphin
- Indo-Pacific bottlenose dolphin
- Indo-Pacific humpback dolphin
- Long-beaked common dolphin
- Killer whale(orca)
- African oystercatcher