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Digitized by Kansas Correctional Industries

Photocopy of typescript. / Digitized by Kansas Correctional Industries

The northern sector of Waihi Beach is an example of chronic erosive tendency. The sediment deficit along the area of beach fronting the seawall means that there is often no beach at high tide. This existing situation, and the various remedial options suggested, has created an emotive issue for beach residents. Accordingly, the current study was undertaken to identify and evaluate the fundamental coastal processes impacting upon the erosion at northern Waihi Beach. Methods used to investigate this problem included: beach profiling and shallow water hydrographic surveying; mapping of sediments and the distribution of bedforms on the inner shelf using side-scan sonar, identification of nearshore sediment transport pathways from sediment textural analyses; collection and analysis of nearshore wave and current data; and numerical modelling of wave refraction and sediment transport processes. A side-scan sonar survey, ground-truthed by surficial sediment analyses and underwater video and diver observations, indicated that the shallow inshore zone is characterised by a relatively featureless seabed dominated by fine sands. Large shore-normal sand ridges (η=0.4-2.5 m, λ=300-1400), with crests oriented northeast to southwest were identified between 15-30 m water depth offshore northern Waihi Beach. These very pronounced features consist of coarse megarippled (η≈0.12 m, λ≈1 m) sediment. Sediment textural analyses revealed that offshore sediments vary from fine to coarse sand, showing a seaward-coarsening progression. Beach sediments consist of predominantly fine sands, with a slight inferred fining in grain size that occurs towards the northern end of the beach. This is possibly a result of lower wave energy when subject to swell and sea waves from the north, due to sheltering in the lee of Rapitiotio Point. 80 days of wave and current data were collected offshore northern Waihi Beach, during two separate deployments in Nov/Dec 2007 and May/June 2008. The summer deployment was characterised by waves from a northeast-east origin (Hs=1.09m; Ts=7.13s). Similar conditions were exhibited during the winter deployment (Hs=0.95m; Ts=6.79s). Observed relationships between wind direction and near-bed current direction, combined with calculated sediment entrainment rates, enabled predictions of the frequency of shoreward sediment transport by bottom currents to be made. Onshore currents, associated with winds from the southwest, prevailed during the deployment period. However, observed current velocities alone were generally incapable of inducing sediment motion. Analysis suggests that wave properties are likely to govern the frequency of sediment transport in the nearshore, as their presence is required to lift sediment into suspension for dispersal by ambient background currents. Onshore movement of sediment was estimated to be ~11,800 m3/year or 2.6 m3/m. Monochromatic wave statistics measured during the field study were used to calibrate a numerical wave refraction model. The wave refraction influence of Mayor Island was found to be the major feature influencing the distribution of wave energy along the shoreline, which is likely to contribute to localised accelerated beach erosion and dune setback. Wave energy focusing at northern Waihi Beach is maximised by swell waves, resulting in greater wave heights along eroding sectors of the beach. Potential sediment transport rates were investigated. Results suggest the littoral drift direction was bi-directional at northern Waihi Beach, although net littoral drift was southeasterly during the study period. An estimated net loss of 46,200 m3/year or 10.3 m3/m was predicted for northern Waihi Beach during the present study. Longer-term drift patterns were examined using a five year record of wave data collected offshore Pukehina by Environment Bay or Plenty from 2003-2008. Similar patterns but with lower magnitudes of sediment transport were obtained, with net annual drift rates estimated to range from 1,300-58,000 m3/year. A conceptual model of nearshore sediment dynamics is proposed for Waihi Beach to identify the major factors contributing to long-term erosion in the northern sector. Approximately 115,000 m3 of sediment was estimated to be moving within the defined northern Waihi Beach littoral cell during the study period. The derived sediment budget produced a net deficit of sediment of approximately 36,000 m3/year or -8 m3/year during the year commencing November 2007. The net southeasterly littoral drift was determined the major contributor to the net erosion rate during the study period, with alongshore transport rates exceeding available supply to the beach from diabathic movement of sediment onshore. Several aspects of the erosion problem at northern Waihi Beach are recommended to be researched further to identify what coastal management options are required.

Excess sedimentation began affecting the wetland dynamics of Pine Gully in Seabrook, Texas during the first quarter of 2004. This sedimentation was sudden and became a serious problem for the dynamics of the Pine Gully wetland because the fine, well sorted, quartz rich sediments began plugging the main channel of the previously tidally dominated wetland. Progressive sedimentation has produced overbank deposits in the marine grasses, contributing to the death of wetland grasses by sediment chocking. The main purpose of this study is to determine the new source and mechanism of sedimentation in Pine Gully, document changes from sedimentation, and determine a solution to prevent future sedimentation. Sedimentation in Pine Gully and coastal areas adjacent to Pine Gully has occurred in a region that has experienced subsidence and sea level rise. The sedimentation in Pine Gully is a direct result of new and sustained sediment at the mouth of Pine Gully. These new sediments are transported into Pine Gully by displacement waves from ships moving through the Houston Ship Channel. Beach renourishment at Wright Beach, located a half mile north of Pine Gully, occurred as Pine Gully experienced sedimentation. Construction of a breakwater at the mouth of Pine Gully and subsequent removal of sediment in Pine Gully itself is ultimately the solution to revitalizing the wetland to its pre-sedimentation state. Replanting of native vegetation killed off by sedimentation is recommended and would hasten the recovery of the wetland. Documenting the effects of this unique sedimentation in Pine Gully has implications for the future. Beach renourishment or coastal projects that may contribute excess sediment to the coastline should be concerned with unintended effects they may cause. Although an historically eroding shoreline exists, the effects of excess sedimentation can be severe. A coastal study should be done before sediment is added to the shoreline to identify any areas within the sphere of influence of the project. Ecosystems determined to be within the sphere of influence by a coastal study should implement preventative measures at those locations to avoid an ecological disaster similar to that in Pine Gully.

Cultural eutrophication is caused by the excess addition of phosphorus to aquatic ecosystems, and has long been a water quality management issue in Lake Erie. Despite successful reductions in external loading of phosphorus in Lake Erie the in lake total phosphorus (TP) concentrations are increasing recently and symptoms of eutrophication are apparent. In this study I examined the sedimentation velocity of particulate phosphorus and how it is affected by stratification and plankton community composition over the growing season. Diatoms had the highest sedimentation velocities and a shift to slower settling species with greater form resistance (Synedra sp. and Fragilaria sp.) was observed during the stratified period possibly in response to the shallower mixed layer. No significant variation in sedimentation velocity was found with trap depth, plankton size or temperature; hence the individual plankton cells were employing methods to change their sedimentation velocity in accordance with changing environmental conditions. Phosphorus sedimentation was most closely related to silica sedimentation, which largely represents the sedimentation of the diatoms. Thus any shifts in community composition will affect phosphorus-settling rates. The sedimentation rate of phosphorus decreased from June 2nd until August 26th during the stratified period at station84 and from June 2nd to August 5th at station 452. The decline of total phosphorus was less than the sedimentation rate, hence, sediment resuspension and redistribution from the littoral sediments along with atmospheric deposition are important sources of phosphorus to the central and eastern basins of Lake Erie. The sedimentation rates of P, N and C did not follow the Redfield ratio. The sedimentation velocity of P was much less than that of C and N, indicating that P is conserved in the epilimnion and possibly that C and sedimentation contains more non-living material. Therefore, modelling phosphorus sedimentation after carbon and nitrogen sedimentation is inappropriate. Laboratory sedimentation towers can be used to measure phytoplankton sedimentation velocity including net upward movement, which traditional sedimentation traps are unable to do. Determination of the sedimentation velocity of the phytoplankton community to variables such as light, temperature and nutrient status, using this method, may eventually lead to a dynamic phosphorus model that could more effectively reduce eutrophication effects in Lake Erie.

Cultural eutrophication is caused by the excess addition of phosphorus to aquatic ecosystems, and has long been a water quality management issue in Lake Erie. Despite successful reductions in external loading of phosphorus in Lake Erie the in lake total phosphorus (TP) concentrations are increasing recently and symptoms of eutrophication are apparent. In this study I examined the sedimentation velocity of particulate phosphorus and how it is affected by stratification and plankton community composition over the growing season. Diatoms had the highest sedimentation velocities and a shift to slower settling species with greater form resistance (Synedra sp. and Fragilaria sp.) was observed during the stratified period possibly in response to the shallower mixed layer. No significant variation in sedimentation velocity was found with trap depth, plankton size or temperature; hence the individual plankton cells were employing methods to change their sedimentation velocity in accordance with changing environmental conditions. Phosphorus sedimentation was most closely related to silica sedimentation, which largely represents the sedimentation of the diatoms. Thus any shifts in community composition will affect phosphorus-settling rates. The sedimentation rate of phosphorus decreased from June 2nd until August 26th during the stratified period at station84 and from June 2nd to August 5th at station 452. The decline of total phosphorus was less than the sedimentation rate, hence, sediment resuspension and redistribution from the littoral sediments along with atmospheric deposition are important sources of phosphorus to the central and eastern basins of Lake Erie. The sedimentation rates of P, N and C did not follow the Redfield ratio. The sedimentation velocity of P was much less than that of C and N, indicating that P is conserved in the epilimnion and possibly that C and sedimentation contains more non-living material. Therefore, modelling phosphorus sedimentation after carbon and nitrogen sedimentation is inappropriate. Laboratory sedimentation towers can be used to measure phytoplankton sedimentation velocity including net upward movement, which traditional sedimentation traps are unable to do. Determination of the sedimentation velocity of the phytoplankton community to variables such as light, temperature and nutrient status, using this method, may eventually lead to a dynamic phosphorus model that could more effectively reduce eutrophication effects in Lake Erie.