MORPHOMETRICS OF CARBONATE TIDAL CREEK SYSTEMS, BAHAMAS AND FLORIDA: IMPLICATIONS FOR TIDAL FLAT RESPONSE TO SEA-LEVEL RISE

Tidal flats are extremely heterogeneous environments influenced by a range of variables acting across several spatial and temporal scales. Given the important role of tidal creeks in sedimentation processes, the goal of this study was to evaluate the dynamics of these systems by quantifying morphometric characteristics of a number of tidal creek networks along carbonate-dominated shorelines in the Bahamas and southwest Florida. Using both aerial photographs and ultra-high resolution remote sensing data, we digitized channel networks and analyzed their attributes using GIS.

In these areas, all tidal creek networks follow Horton’s laws of stream numbers and lengths. Network characteristics for systems within each area are consistent, indicating similar fractal scaling properties. For both areas, there is an inverse relationship between mean sinuosity and order, except for first and second order streams, which are straighter than expected given the trend in higher order streams. Plots of log of exceedance probability versus channel length for networks on Andros Island illustrate trends consisting of two linear segments (exponential distributions), with decrease in slope for different networks at lengths between 300-500 m, indicating that there are more shorter streams than expected given the number of longer streams. The system in southwest Florida shows a similar bend at shorter lengths, but also includes an increase in slope at longer lengths.

The results from both areas illustrate that, relative to trends in higher order and longer creeks, lower order creeks are straighter and more abundant than expected. Our current interpretation is that these trends reflect the system’s response to the recent relative rise in sea level (since 1930, a rise of ~22 cm in Florida). As sea level rises, with each tide a larger volume of water is exchanged with the tidal flats, resulting in higher energy flow conditions in the channels. Existing shorter, lower order creeks are likely the quickest to respond to these hydrodynamic changes by straightening and extending. Similarly, new, straighter first-order creeks are forming.

Understanding and quantifying the morphometrics of modern tidal systems provides important data for predicting future responses to external change, as well as understanding ancient tidal flat systems.