ASSIGNMENT 2 – Onshore-Offshore Onshore-Offshore Sediment Transport CVEN 9640D – COASTAL COASTAL ENGINEERING Due Week 9 – Friday, Friday, May 6, 2016 Submit as a pdf by email to
[email protected] by 5pm on 6/5/16. ASSIGNMENT SCOPE
For this assignment you will be running the SBEACH model to familiarize yourself yourself with an engineeringscale working cross-shore sediment transport model commonly used in Coastal Engineering Consulting. The assignment assignment is being set up as a consulting brief in which you will run the model and provide engineering advice to your client in the form of an engineering report. You will need your notes from “Beaches, Hazards, Climate Change” and “Cross“Cross -shore Sediment Transport” along with handouts provided in the Assignment Assignment 2 Folder Folder on Moodle and any other reports/papers reports/papers you you see fit. You have been asked by Tigard Council to develop Coastal Hazard lines for a beach in which new development development is proposed along high value coastline. The council requires lines for present day as well as 2050 and 2100. See Figure 13 (“Beaches, Hazards, Climate Change”) for example and Nielsen et al. al. (1992). Background information: The beach currently has a long-term recession rate of 0.2 m/yr. Assume no erosion due to longshore transport gradients or to beach rotation. Sea level rise for the area has been adopted as 0.4m (2050) and 0.8m (2100). Council has adopted that storm erosion demand is based on 2 back to back 100yr ARI storms. The effective grain size (D 50) is 0.35mm. SBEACH MODEL:
The model and various help and data files are located within the .zip file “SBEACH 2000” (32bit) or “SBEACH 64bit” (64bit) which are on Moodle. Install the appropriate version of the SBeach model and load the existing project “Assignment.SB”. “Assignment.SB”. Familiarise yourself with the operation of the model by running various combinations of the profile and storms pre-loaded pre-loaded within the t he “Assignment.SB” “Assignment.SB” project file. IMPORTANT – Make – Make sure you you save a copy of the original “Assignment.SB” “Assignment.SB” file. file. For the final model run you write your report on, restart SBeach and run the original model setup with the modified design conditions. ASSIGNMENT TASKS
1 - You are required to run the model using the Narrabeen Malcolm St August 1986 profile and assess your expected uncertainty in your results based on the calibration to the “Narrabeen “Narrabeen Malcolm St August 1986” storm. NOTE: use the existing parameters parameters given given in SBeach for your analysis. analysis. You may wish to change parameters parameters to show you understand understand model model sensitivity. For the default values, discuss discuss briefly:
The patterns of beach volume change, where is sand moving and why? Is the total volume conserved?
Rates of shoreline recession/beach volume change above MSL at different times during the model run (Hint – see figure 2 in your Cross-shore Sediment Transport notes). For beach volume change, assume the total volume (ie integrated in the cross-shore) between x=0 (the most landward grid point) and the shoreline (MSL). Can any of your observations be explained in terms of the model formulation (Hint - see section 1.4.2 of your Cross-shore Sediment Transport Modelling notes)?
2- Utilize SBeach and the “100yrARI_queensland” storm provided to calculate an appropriate storm demand volume (measured above 0m AHD) based on the background information above (ie 2 back-to back 100yr ARI storms).
How does your estimated erosion volumes above MSL (storm demand) compare to those commonly reported by Gordon (1990) for the 100 yr ARI storm. (HINT: see figure 2 in Nielson and Adamantidis, 2007). Using the approach outlined in Nielsen et al. (1992) use the erosion volumes estimated in SBeach to calculate the Zone of Wave Impact and the Zone of Slope adjustment. Assume a natural angle of repose of 34 degrees. Assume the top of swash is at 2m AHD.
3 – Estimate the zone of reduced foundation capacity following the approach of Nielsen et al. (1992). Assume the depth of scour is -1m AHD. 4 – Estimate recession due to SLR for 2050 and 2100 based on the Bruun Rule. Depth of closure can be estimated from the equations in your “Cross-shore sediment transport” notes. Berm height can be estimated from the profile data given in t he SBeach Assignment SB. Depth of closure (hc) can be assumed to be 15 m. Clearly state your assumptions in the report. 5 – Combine your knowledge of the long-term recession rate, design storm erosion demand, SLR recession and zone of reduced foundation to provide council advice on where the present, 2050 and 2100 coastal erosion hazard line should be. Make your distances relative to the present day x=0 which coincides with the top of the dune. Discuss what factors of safety are included in this methodology. Based on your reading and knowledge so far, comment on how this approach could be improved. SUBMISSION
Write up your results in a concise engineering report with correctly and clearly labelled sections, figures, tables and a bibliography. Your report should include a title page, table of contents, executive summary, proper introduction, model description, engineering findings and a conclusion. Each figure/table should support your writing (Do not provide a dump of figures). HINT: The easier you make it for your marker to identify the key deliverables, the better chance of getting marks. The report cannot exceed 20 pages (1.5 spacing) excluding your title page, table of contents, and executive summary. Appendices can be provided for calculations if you see fit but these will not be necessarily marked.
