GLY 4552 Sedimentary Geology Fall 2007 BEDFORM MAPPING IN A COASTAL ENVIRONMENT, HUGUENOT MEMORIAL PARK, FLORIDA OVERVIEW Bedforms provide the link between flow conditions and sedimentary structures that are preserved in the geological record. In order to understand bedforms and their formative flows, you will investigate a portion of Huguenot Memorial Park in coastal Florida. During the exercise, you will (1) learn to recognize and map diverse bedforms in the field, specifically a barrier beach/inlet/flood-tidal delta complex at Huguenot Memorial Park in coastal Florida, and (2) relate qualitatively bed configurations to flow conditions (depth, velocity, relative importance of currents/waves/wind). PREDICTION (This portion of the exercise is due the class before the field trip.) Study the map/photo of Huguenot Memorial Park provided within this lab, noting the sandy coastal barrier that absorbs much of the energy of breaking waves from the Atlantic Ocean. Twice a day, the ~2.6 m tide rises against the shore, flooding through a ~300-m-wide tidal inlet to inundate a sandy back-barrier tidal river which is fringed by tidal marshes. Following highBedform Analysis p. 2 tide, the water in this back-barrier setting collects and returns through the inlet to the sea. We will be visiting the site near the time of low tide. Note the following environments labeled on the map and use the enclosed table to predict what bed forms/configuration you expect to find when we visit the site at low tide: A. Nearshore breaker zone B. Foreshore swash zone C. Tidal-inlet channel D. Back-barrier channel E. Back-barrier slope F. Backshore G. Proximal tidal delta H. Distal tidal delta You will not be graded on these predictions—rather they will form a basis for comparison and reflection after you have visited the field. Remember that it takes a while for bedforms to respond to changing flow conditions, so the bedforms at the surface may reflect the latest flows only partially or not at all. In general, bedforms created by the strongest flows at a site will tend to persist, albeit sometimes as modified forms. On one of the blank maps, sketch in a prediction of what major bed forms/configurations you expect to find across the area (not just at the arrowed sites) when we visit the site at near-low tide. Use (and modify as needed) the following key: Upper-stage plane bed; N-S current lineation 2-D (straight-crested) dunes; flow to NE 3-D (sinuous-crested) dunes; flow to SW Wave ripples; straight crests E-W Sinuous current ripples; flow to S Antidunes; flow NW or SE Eolian (wind) ripples; wind to N EFort George Inlet, FloridaA. Nearshore Breaker ZoneB. Foreshore Swash ZoneC. Tidal Inlet ChannelD. Back-barrier channelE. Back-barrier slopeF. BackshoreG. Proximal Tidal DeltaH. Distal Tidal DeltaNorth100 mPREDICTED BEDFORMS (complete and hand in at class before day of field trip) Environment Comments Predicted bedforms (include orientation, e.g., flood or ebb) Reasoning A Nearshore breaker zone zone where incoming waves slow up, build higher, and break B Foreshore swash zone broken waves rush up beach face, stall, and flow back down slope C Tidal-inlet channel ~300 m wide and ~100 m wide at low tide; usually fastest flow in system D Back-barrier channel ~70 m wide and ~50 m wide at low tide; E Back-barrier slope steep (near angle of repose), ~2-m slope from backshore to tidal channel F Backshore flat, unvegetated zone normally flooded only by highest tides G Proximal tidal delta sandy depositional area ~400 m landward of tidal inlet H Distal tidal delta sandy depositional area ~700 m landward of tidal inlet Bedform Analysis p. 4Bedform Analysis p. 5 OBSERVATION (This portion of the exercise is completed during the field trip.) In the field, you will work in teams of 3-4 to describe and map bedforms. Take a few moments to orient yourself to the overall setting, after which we will examine a few selected areas to familiarize you with features and terms. Then begin your mapping, trying to hit the topographically lowest areas near the lowest tide, and leaving higher areas for before and after. For each environment listed in the following table and as shown on the map, select a representative area, and describe the bedforms and bed configurations, noting relevant details of size (wavelength and height), continuity and sinuosity of crest lines, orientation of crest lines (both qualitatively [i.e., flood- vs. ebb-oriented] and measured with compass), and grain size. Try to explain the characteristics and sequences of the formative flows in terms of depth, speed, direction, and type of flow [unidirectional currents, oscillatory or combined flow]. For each area, take a GPS reading and 1-3 digital photographs of the bedforms, making sure to include a scale and group name in each. As time permits, try to map in the major bedforms in the whole of the study area. COMPARISON (This portion of the exercise to be completed and handed in at the class following the field trip). For each of the listed environments, compare your predictions and observations of bedforms and interpreted formative flows in the study area. Briefly explain the differences between predicted and observed, noting what additional insights you gained from the field experience. Digital photographs and GPS data will be compiled for the class into a GIS overview of bedforms in the study area. Use the resulting map and data to write a succinct summary of the major patterns of flow in the barrier beach/inlet/tidal-delta complex.Bedform Analysis p. 6 OBSERVED BEDFORMS (complete during field trip) Environment Observed bedforms (include wavelength & height, orientation, e.g., flood or ebb) Interpretation of formative flows GPS coordinates and digital photo numbers A Nearshore breaker zone B Foreshore swash zone C Tidal-inlet channel D Back-barrier channel E Back-barrier slope F Backshore G Proximal tidal delta H Distal tidal