You could do all kinds of things. You could:

-Try to measure the abundances of different life forms on the shoreline (an ecology project).
-Try to measure whether a given species is found only in specific locations (and if so, which) along the shoreline (another ecology project).
-Measure when certain spots protected in tide pools or behind cliffs, etc. are under water with the tides (an astronomy/planetary science project).
-Measure the pH of the mud as a function of depth under the ground surface at a given location on a mudflat (a geochemistry project).
-Measure the difference in weight between wet sand and dry sand at different levels of the beach, and thus calculate the amount of water within (a hydrology project).

For the local shoreline project, I can suggest doing an experiment measuring the speeds of the long shore current and long shore drift. Both of these are discussed in oceanography textbooks. There is an experiment for measuring the speed of the long shore current on YouTube
longshore current.

You can determine the speed of the long shore current by conducting the following simple group experiment.

You will need a meter stick (or other measuring device) an orange or two, a watch with a second hand and a group of students. Use the other side of this worksheet to enter and calculate your data.

Procedure:
Measure off and draw a ten-meter line in the sand parallel to the ocean. Position one student at each end of the line you have drawn. Position everyone else along the line. One student should assume the role of timekeeper and have a watch with a second hand.
Throw an orange (or a piece of driftwood) into the water, just behind the line of breakers, approximately 2 meters SOUTH of the beginning of your line. Note: The long shore current is closer to the shore than you might expect! All students should watch the orange as it moves. When the orange passes the beginning of the line the timekeeper should start timing. When the orange passes the person stationed at the end of the line, he or she should tell the timekeeper to stop timing. Record time on worksheet.

If time permits, repeat this process again so you can calculate the average of the two (or three) trials. Calculate the speed of the long shore current for both trials, and then calculate the average of the long shore current today. This procedure is NOT fool proof. If your orange does not move north after a few minutes, try again. If you cannot get this to work at all, it may be due to weather conditions. Try again tomorrow!

Formula: distance/time = speed

Well, to answer your question broadly, there are literally thousands of projects that one can do on local shorelines! It sounds like you are looking for a field-based project, one where most of your data is collected from real coastal settings rather than collecting specimens or samples and bringing them into controlled environments.

An easy way to start considering these systems is by thinking ecologically. For example, what types of plants/animals/algae are in local coastal habitats? Does the diversity/abundance/size/etc. of species differ between different types of shoreline (rocky, sandy, mud, protected, shaded, etc), or between different tidal heights (high on the shore vs. lower on the shore)?

You could easily pick a couple types of organisms and follow them across various sites. Perhaps you can try to put them into a bigger picture - how do your findings relate to what we know about predator/prey relationships? Can you relate the findings to location differences (areas that get different amounts of human activity, or with differing proximity to industrial areas like marinas or sewer run-off sites, etc)?

You could also look at the characteristics of habitats themselves - for example, you could examine tide pools of different sizes/sun v. shade/depth and measure how quickly they heat up during low tides on sunny days and cloudy days, and the different numbers and kinds of organisms found in each one.

You could look at water differences, like salinity or chemicals in various areas. Or collect water samples and observe the resident plankton densities/diversity under a microscope and relate it to the organisms on that shoreline, or to currents and the area's exposure to open ocean water sources.

Most of these ideas are ecology-based (since I am an ecologist), but there are plenty of other directions you can go in depending on your personal interests. Maybe you can just take an hour or two and go to your local beach and see what catches your eye. You can get a lot of really interesting information about coastal areas by taking the time to bend down and look closely at the marine life there. Then you can start thinking about how an organism's survival is affected by its biological and physical interactions with its surroundings.
Good luck!!

Wow, there's a whole range of things you could do!
You could survey the distribution (high/low shore, or sandy/rocky beaches, or wavy/protected areas) and abundance (ie # organisms per unit area) of shoreline plants and animals, and see how these distributions change as you go to different areas.

You could measure the growth of small sessile (non-moving) invertebrates like barnacles or mussels or algae by measuring them at repeated intervals of time. Since spring is coming, you could look at the recruitment (appearance) of new organisms on rocky shores over a period of a couple of months and see what species appear and what their densities (# organisms per unit area) are.