#20 L2 Mastering Coastal Sediment Sources: Terrestrial, Offshore and Human Inputs | Coasts | A Geography

This podcast explores coastal landscape systems to uncover the three vital sediment inputs: terrestrial, offshore, and human management. From massive river discharges and dramatic cliff collapses to the high-tech rainbowing of beach nourishment, we explore how sediment budgets stay balanced. Whether you are an A-level student or a teacher looking for engaging case studies like Dubai’s Palm Jumeirah, this is your ultimate guide to coastal dynamics.

Watch video versions of these podcasts on YouTube for a more dynamic experience. Browse our playlists on our channel here WGSG Geography - YouTube 

Transcript

SPEAKER_00 0:00

Welcome to this explainer on coastal landscape systems. You know, when we think of the coast, we usually just picture a nice static beach for a summer holiday. But actually, it's a dynamic, living, breathing machine. And like any massive engine, it needs fuel to run. For the coastal environment, that fuel is sediment. Today, we're going to track exactly where this material comes from, mapping out the complex environmental pathways that keep our coastlines moving. Okay, here's our game plan. First, we'll define the coastal system itself. Then we'll break down the three main input factions, terrestrial sources, offshore sources, and human inputs. After that, we'll lock the pieces together in the complete system and finally wrap things up with a quick exam review. Right, let's jump straight into section one, the coastal system. If you really want to nail A-level geography, you've got to stop looking at coasts as just scenery and start seeing them as systems. It's basically a giant environmental loop. You've got inputs, which is the fresh sediment entering the arena, you have transfers, the wind and water physically moving that material around, then there are stores, like beaches and dunes where the sediment basically just hangs out, and eventually outputs where material is washed out for good. But today, we are hyper-focusing solely on those inputs, the loose, unconsolidated sediment acting as the primary fuel for the whole shebang. When we look at how this all works, we're essentially tracking plastic sediment. That's really just a fancy term for broken down rock fragments. This stuff comes from all over the place, washing down rivers, crumbling off cliffs, or rolling in from the deep sea. But the key thing is, once it hits the coastal zone, it gets entrained. Entrainment is literally just moving water or air, grabbing onto those stationary particles, saying, you're coming with me, and pulling them onto the board. Moving on to section two, terrestrial sources. Now, terrestrial or land-based inputs are absolutely massive. And rivers, they are the undisputed heavyweights here. You might think cliffs do most of the work, but rivers actually provide up to 80% of all coastal sediment in some locations. Most of this is fine sand and silt coming from inland denudation, which is just the wearing away of the Earth's surface. And it doesn't just trickle in nicely. A lot of the time, this sediment gets blasted into the coastal zone during huge, intermittent, high-energy flood events. But hey, we definitely can't ignore the cliffs. While rivers give a steady volume, weak cliffs battered by destructive waves give us these violent, explosive inputs. Take the infamous 2013-14 winter storms at Dawish in South Evan. We had massive storm surges, these temporary local rises in sea level driven by low pressure, just hammering the coast. In localized high-energy spots like that, cliff erosion can actually supply up to 70% of a beach's overall sediment. It usually starts off super coarse like huge rocks and boulders before getting smashed down over time. So we've got sudden cliff collapses and river floods, but backing all that up are the steady, everyday transfers. Think of longshore drift like a relentless conveyor belt, constantly shuffling sediment from one stretch of coast to the next. Add in aeoline or wind processes, where the breeze picks up fine sand from the dunes and blows it inland, and you've got a system that is literally always redistributing its wealth. Let's hit underwater for section three, offshore sources. You know, the sea doesn't just take land away, it gives it back too. During the calmer summer months, constructive waves act as our steady builders. Because they have a really strong swash and a super weak backwash, they grab fine marine sediment from offshore and push it right onto the beach. It's this exact marine deposition that builds up those higher, gentle beach profiles we all love to lounge on during summer holidays. But we've got to distinguish between the different jobs water does here. Constructive waves are building the beaches directly, sure. But tidal streams and onshore currents, they are busy shifting fine sediment into foreshore sandbars. And here's why that actually matters. At low tide, those sandbars stick out and dry off in the sun. Once that sand is completely dry, those aeolian wind processes we talked about earlier can easily scoop the grains up and blow them inland, adding yet another dynamic loop to the sediment budget. Alright, section four. Human inputs. Sometimes a coastal sediment budget falls into a deficit. That basically means more sand is leaving the system than coming in. When that happens, the beach shrinks and the land behind it gets incredibly vulnerable to storm surges. So what do we do? We step in and forcefully restore equilibrium through beach nourishment. We literally artificially feed the beach. Picture hundreds of lorries dumping sediment on the shore, bulldozers spreading it all out, and these low clay banks called buns holding it all in place while the seawater drains away at low tide. And if you want to see something really wild, there's a high energy tactic known as rainbowing. This is where a massive offshore barge blasts a thick slurry of dredge sand and seawater in this giant arc straight onto the coastline. It literally looks like a sand rainbow. By artificially plumping up the beach this way, we're building a crucial shock absorber that takes the hit from wave energy and defends the land from long-term erosion. But for the absolute pinnacle of human input, we have to talk about mega projects in Dubai, like the Palm Jumara and the World Archipelago. Here, they aren't just topping up a struggling beach. They are literally redrawing the map. By dredging up millions of tons of offshore marine sediment and intentionally placing it to create brand new artificial islands, it demonstrates human sediment input on a scale that is almost unbelievable. Bringing it all together in section 5, the complete system. When you're standing on a coast, you are looking at a battlefield where all these inputs are constantly interacting. You've got terrestrial rivers dumping inland dirt, constructive offshore currents dragging up ancient marine deposits, and human megaprojects fighting against erosion. All of these dynamic inputs feed into the coastal stores, constantly fighting to maintain a delicate balance, or equilibrium. It's this endless, beautifully complex machine of inputs, transfers, stores, and outputs working together. Okay, section six, exam review. Let's get you prepped. For your exams, you absolutely have to remember your critical power level stats. Terrestrial inputs are the kings. Rivers supply up to 80% of coastal sediment, while high-energy storm erosion on cliffs can hit up to 70% locally. For offshore, just remember that constructive waves are your summer beach builders, and finally, human inputs, like beach nourishment and rainbowing, are artificial fixes when a coastal system falls into a sediment deficit. Lock those numbers and concepts in, and you're going to absolutely crush any question on sediment sources. But before we wrap up this explainer, I want to leave you with a real hinge question to chew on. As climate change continues to alter the board and rising global sea levels throw more of our coastal budgets into severe deficits, how is this balance going to shift? Are we going to be forced to endlessly escalate our artificial inputs, dumping more and more sand just to save our current coastlines? Think about the long term sustainability of that constant intervention. It's a massive challenge for the next generation of geographers, which means it's a challenge for you. Thanks for hanging out with me today. Keep studying hard, and I'll catch you in the next one.