In additon to the websites already mentioned, I can also recommend http://tryengineering.org/.
There are several end products of engineering design that you can choose from: theoretical plans; models; list of procedures; and, finally, prototypes or actual working designs. I have also attached a library of engineering design process lessons.
Here are a few possible design projects that come to mind loosely organized by engineering disciplines.
· migration corridors for different species. Start with a case study on how engineers helped organisms safely migrate across major highways and other human-made barriers.
· irrigation systems to minimize erosion.
· campgrounds in a park to have a zero-carbon footprint and be ecologically unobtrusive.
· Waste handling systems
· Reclaiming plastics from oceans
· Use geographic data to place a hydroelectric dam in the most advantageous and least disruptive location for an ecosystem and watershed.
· traps to safely capture organisms.
· Artificial limbs and organs for animals or humans. This also allows you to incorporate 3D printers for prototyping.
· Use computer probes to collect data on heart rate, oxygen, and so on.
· Systems to protect jets and airports from birds.
· Collect environmental data using drones or weather balloons.
· Use microprocessors like Arduinos or Raspberry Pi and program sensors to collect physical data on habitats, aquaria, terrariums, etc.
· Create enclosed habitats or greenhouses that collect data and respond to changing conditions.
Hope this helps!