Uilkraals Situation Assessment - Anchor Environmental

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Figure 9. An aerial view of the Uilkraals Estuary mouth in October 1979 (altitude of 500m).When functioning naturally, the river enters the sea via a meandering channel across thefloodplain, which opens onto sand flats (Heydorn & Bickerton 1982). The road bridge crossesat the lower reaches of these sand flats. There are several river channels which flow across thesand flats upstream of the bridge (Heydorn & Bickerton 1982). The mouth was originallymobile and in the past could enter the sea at any point between the eastern dune and westernpart of the beach opposite the caravan park (Heydorn & Bickerton 1982). The mouth laterbecame fixed by a combination of factors, including the causeway of the road bridge and thestabilization of both the eastern and western dunes (Heydorn & Bickerton 1982).Figure 10. Picture of the bridge and causeway of the Uilkraals Estuary facing downstream.Uilkraals Estuary Situation Assessment19Anchor Environmental
The first time in recorded history that the Uilkraals Estuary became closed for a long period oftime was in January 2009. It re‐opened six months later for a short period but closed again foran extended period in December 2009. Water storage in the Kraaibosch Dam, approximately10 km upstream from the estuary, has significantly altered the natural freshwater in‐flows tothe estuary while agricultural activities in the upper catchment have introduced an increasedsediment load into the estuary, ultimately resulting in reduced flow over time and an increasedlikelihood of mouth closure of the estuary in low flow periods.The lower reaches of the estuary used to consist of several braided channels that expanded toa single 400 m wide channel at high tide (Harrison et al. 1995b). Water in the area below thebridge is now restricted to two smaller shallow channels, the larger of which ends at the beachin front of the huts at the caravan park (Figure 11). Before mouth closure occurred, tidalinfluence reached beyond the bridge, with the majority of the sandflats becoming inundated athigh tide (Harrison et al. 1995b). Tidal interchange was recorded up to 3 km upstream in a1981 survey (Heydorn & Bickerton 1982). Currently, a very shallow braided channel runsacross the sandflats upstream from the bridge, probably similar to former low tide conditions.The majority of the sandflats are now permanently exposed (Figure 12).Figure 11. The closed estuary mouth facing upstream (left) and the area below the bridge facingdownstream (right, picture taken from the bridge), February 2010.The middle reaches of the estuary consist of a wide meandering channel across a largefloodplain, surrounded by saltmarsh vegetation. Before the road bridge was built, the estuarywas a marine‐dominated tidal lagoon. The large volumes of tidal exchange would have rapidlyreduced any effects of floods, when they did occur (Gaigher 1984). Factors affectingcirculation also affect salinity by altering the volumes of salty water entering the estuary aswell as the ratio of dilution of fresh and salt water (Clark 1977). The obstruction caused by theroad bridge would therefore have changed the circulation and hence salinity regime of theestuary immensely. This would have been most critical during periods of freshwater flooding,by prolonging the extension time of freshwater over tidal sandbanks. This effect would havebeen most intensive in the extensive flood area on the landside of the bridge (Gaigher 1984).Uilkraals Estuary Situation Assessment20Anchor Environmental
Page 1: C.A.P.E. Estuaries Management Progr
Page 6 and 7: Need for protection of the Uilkraal
Page 8 and 9: TABLE OF CONTENTS1. INTRODUCTION...
Page 10 and 11: 1. INTRODUCTIONThe Uilkraals Estuar
Page 12 and 13: 2. GEOGRAPHIC AND SOCIO‐ECONOMIC
Page 14 and 15: 2.2 Catchment climate, vegetation a
Page 16 and 17: Figure 7: Annual rainfall for the U
Page 18 and 19: EconomyAgriculture dominates much o
Page 22 and 23: Figure 12. Pictures of the exposed
Page 24 and 25: 3.4 VegetationThere are four main v
Page 26 and 27: covered 19 ha and grassland 1.3 ha.
Page 28: Because the Uilkraals Estuary is ca
Page 31 and 32: For this study, a count of water‐
Page 33 and 34: iophysical variables. The current s
Page 36 and 37: Table 8. Ecosystem goods, services
Page 38 and 39: Estuaries are typically shallow and
Page 40 and 41: strands of remnant undisturbed fynb
Page 42 and 43: • to have the environment protect
Page 44 and 45: ProtectedareasUse of living resourc
Page 46 and 47: Table 11.Goals and strategies in th
Page 48 and 49: 5.3 Water quantity and quality requ
Page 50 and 51: Development planning has been rathe
Page 52 and 53: and weakening or destruction of the
Page 54 and 55: • take into consideration whether
Page 56 and 57: principles involve identifying an o
Page 58 and 59: Component Strategy with spatial imp
Page 64 and 65: Component Description PoliciesConse
Page 66 and 67: Component Description PoliciesCore
Page 68 and 69: Other recreational activities are o
Page 70 and 71:
2. Establish a Marine Protected Are
Page 72 and 73:
Gillanders, B.M. & Kingsford, M.J.
Page 74 and 75:
APPENDIX 1: TERMS OF REFERENCEThe d
Page 76:
6. Monitoring and evaluationAn appr
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