Taming the lagoon

“For hours we drove by taxi to a little river deep in the jungle. From there a small boat took us to the coast, to the headquarters of Pacuare Nature Reserve”, hydraulic engineering student, Frank Melman, laughingly recalls. “To get to that nature reserve for turtles you have to perform quite some tricks. It’s really in the middle of nowhere.”

Last autumn Melman and three fellow hydraulic engineering students, Sander Post, Viannette den Boer and Dennis Joosten, spent three weeks in that remote place, modeling the local hydrology. Small as it may be, this little river poses a threat to the nature conservationists, just as the poachers do to the sea turtles that lay their eggs along the shoreline each summer. The students’ objective was to analyze the river and coastal morphology, in order to provide recommendations for the safe discharge of water during the winter months.
One branch of the water system ends in a lagoon that is separated from the ocean by a 100-meter wide strip of beach. Or so it is under ideal conditions. The problem is that, due to heavy rainfall, the lagoon regularly overflows in winter, flooding the beach. The homes of the conservationists meanwhile are built right at the corner where river and ocean meet. With the beach gone, ocean waves and strong river currents gnaw at the pole bases of the conservationists’ homes.

Not very smart to build your living quarters right on that particular spot, one would think. But Melman disagrees: “I wouldn’t say it was stupid. The Englishman John Denham, who first started working as a conservationist in the park in 1989, couldn’t have known about the dangers. There was no scientific knowledge about the river dynamics at that time.”
And what’s more, the water problems have increased since 1989, owing to an increase in upstream banana crops. In order to cultivate areas along the river that normally flood in winter, the farmers built dikes, which, consequently, means more water flows towards the lagoon.
Somewhat to their surprise, the students found that the hydrological model they developed seems to be fairly accurate. They had predicted that if a lagoon a few miles away was to overflow this winter, the beach next to the conservationists’ homes would remain intact. Since the two lagoons are connected to each other by inland waterways, if one of the lagoons overflows, the result is less water buildup in the other lagoon.
And this exact scenario occurred. Farmers, who wanted the water level in the canals to decrease, dug a channel in the beach in front of the other lagoon. As a consequence of this, the water level in the lagoon next to the conservationists’ homes lowered exactly as much as the students had predicted.

Adding to their thrill of discovery was the fact that the students developed their model with very basic equipment. The most sophisticated gear they used was a little boat outfitted with GPS and sonar equipment to measure the depth of the water along the river.
Other parameters were obtained more primitively. “We used intuition to estimate the height of the dikes”, Post explains. “And we used two Coca Cola bottles tied together to measure the current: one of them empty, the other filled with sand. When you throw them in the water and measure the speed of the floating bottle, what you’re actually measuring is the speed of the current deeper in the river, which is what you need in a hydrological model.”
Removing the dikes along the banana plantations would be one solution for preventing erosion; however, a more practical solution for the conservationists is to reinforce their lagoon with sandbags and dig a small channel each winter in the other lagoon.

“Of course the best solution – also for the turtles – is beach nourishment, the adding of sand from the ocean to the beach, as we do in Holland”, Melman says.
“But that’s not going to happen”, Post counters, “because it’s too expensive. It would’ve been different if there were tourists there, but the tourists are all on the west coast, which isn’t surprising. You can’t swim in the ocean there because of the rip currents and the lagoon is full of crocodiles. But worst of all are the sand fleas: they drove us crazy!” 

Het dagelijks verkeersinfarct op de A15, de hoofdverbindingsader van de Rotterdamse haven, is zowat vanzelfsprekend. Een typisch voorbeeld van een diffuse vervoersvraag, weet prof.dr. Henk van Zuylen van de sectie transport en planning bij CiTG. Kenmerken zijn: een ruimtelijke spreiding van de bestemmingen, een lage vraag per vierkante kilometer en een vervoersvraag die zich over de hele dag, dus ook buiten de spits, verspreidt. Dan bieden bus, trein, tram en metro geen uitkomst. Kan het personenvervoer ook anders, zodat het vrachtverkeer meer ruimte krijgt? Jazeker! Het Personal Rapid Transit systeem (PRT) is veilig, snel en altijd beschikbaar. Bij een terminal geef je op waar je wilt zijn in de haven. Binnen twee minuten zoeft een elektrisch karretje voor met plaats voor vier personen.  Dit vindt met een gangetje van veertig kilometer per uur zelfstandig zijn weg over speciale paden. Omdat iedere bestemming aan een eigen aftakking van de baan ligt, kan het overige verkeer ongehinderd doorrijden. Invoegen gebeurt automatisch.  In het Engelse Cardiff werkt PRT op de proefbaan en dit najaar wordt een dergelijk systeem van het merk Ultra in bedrijf genomen op de Londense luchthaven Heathrow. Van Zuylen denkt dat zo’n systeem ook in de haven een uitkomst kan bieden. Hij heeft een aantal onderzoekers gevraagd een haalbaarheidsstudie uit te voeren. Het eindrapport moet eind 2009 klaar zijn. Het systeem heeft ook milieuvoordelen. Zelfs bij een lage bezetting van 1,4 personen en 40 procent lege ritten levert het een energiebesparing van 75 procent op ten opzichte van de eigen auto. Helemaal mooi wordt het als de baan uitgerust wordt met zonnepanelen en hier en daar een windmolen. Daarmee kan naar schatting 60 tot 80 procent van het energiegebruik worden opgewekt.