Coastal Systems and Landscapes Overview | 海岸系统与景观概述

📚 Coastal Systems and Landscapes Overview | 海岸系统与景观概述

Coasts are among the most dynamic environments on Earth, acting as open systems where energy, sediment, and water continuously move across the boundary between land and sea. Understanding coastal systems is essential for explaining the formation of distinctive landforms and for evaluating the impacts of human activity and climate change.

海岸是地球上最具动态性的环境之一，作为开放系统，能量、沉积物和水持续在陆地与海洋的交界面上流动。理解海岸系统是解释特殊地貌形成、评估人类活动与气候变化影响的基础。

1. The Coast as a System | 作为系统的海岸

A coastal system is best understood as an open system, meaning it exchanges both energy and matter with its surroundings. It receives inputs such as wave energy, wind, rainfall, and sediment from rivers or cliffs; stores material in beaches, dunes, and offshore bars; transfers it through longshore drift and tidal currents; and loses outputs such as sediment moved beyond the coastal zone or eroded material washed out to sea.

海岸系统最好被理解为一个开放系统，即它与周围环境交换能量和物质。它接受波浪能、风、降雨以及来自河流或悬崖的沉积物等输入；将物质储存在海滩、沙丘和近岸沙坝中；通过沿岸漂移和潮流进行搬运；并以沉积物移出海岸带或侵蚀物质被冲入海洋等形式产生输出。

Inputs → Stores → Transfers → Outputs

This systems approach allows geographers to treat a coastline not as a fixed line on a map, but as a set of interrelated components whose balance determines whether a coast is eroding, stable, or accreting.

这种系统方法使地理学家不再把海岸线视为地图上的固定线条，而是将其视为一组相互关联的组成部分，它们之间的平衡决定了海岸是侵蚀、稳定还是淤积。

2. Energy Inputs: Waves, Tides, and Currents | 能量输入：波浪、潮汐与洋流

Waves are the dominant energy input in most coastal systems. Wave energy is controlled by wind speed, wind duration, and fetch — the distance of open water over which the wind blows. Longer fetch and stronger winds generate more powerful waves with greater erosional capacity.

波浪是多数海岸系统中占主导地位的能量输入。波浪能由风速、风时和风区长度（即风在水面上吹过的开阔水域距离）控制。风区越长、风速越大，产生的波浪就越强，侵蚀能力也越大。

Constructive waves have a strong swash and weak backwash, so they build up beaches and promote deposition. Destructive waves have a weak swash and strong backwash, so they scour sediment seaward and promote erosion. Tides, caused by the gravitational pull of the Moon and Sun, alter the vertical range of wave attack.Fetch and tides together determine the height and reach of waves. In addition, tidal currents and ocean currents transfer sediment along and across the coast, and wind moves sand in coastal dunes.

建设性波浪涌升强、回流弱，因此能堆积海滩、促进沉积。破坏性波浪涌升弱、回流强，因此会把沉积物向海方向冲刷，促进侵蚀。潮汐由月球和太阳的引力引起，改变了波浪作用的高度范围。风区长度与潮汐共同决定波高和波浪达到的范围。此外，潮流和洋流沿纵向和横向搬运沉积物，风则搬运海岸沙丘中的沙子。

3. Sediment Sources, Stores, and Sinks | 沉积物的来源、储存库与汇

Sediment in a coastal system comes from several sources. Rivers supply vast quantities of sand and silt; cliff erosion releases material directly onto the shore; biogenic sources, such as shell fragments and coral debris, contribute to carbonate beaches; and glacial deposits may be reworked by waves. In many places, offshore sediments are pushed onshore by waves during fair-weather conditions.

海岸系统中的沉积物有多个来源。河流输入大量沙和粉砂；悬崖侵蚀直接把物质释放到海岸；生物源如贝壳碎屑和珊瑚残体构成碳酸盐海滩；冰川沉积物也可能被波浪重新改造。在许多地方，近岸沉积物在天气良好的条件下被波浪推向岸边。

Stores are temporary accumulations of sediment, including beaches, dunes, spits, tombolos, and offshore bars. Sinks are long-term deposits such as deep-sea basins or river deltas that remove sediment from the coastal system for geological timescales.

储存库是沉积物的临时堆积体，包括海滩、沙丘、沙嘴、陆连岛和近岸沙坝。汇是长期沉积场所，如深海盆地或河流三角洲，它们在地质时间尺度上使沉积物脱离海岸系统。

4. The Sediment Cell Concept | 沉积物单元概念

A sediment cell, also called a littoral cell, is a self-contained coastal compartment with clearly defined boundaries. Within a cell, sediment is moved by waves and currents from a source through transfer zones to a sink, with relatively little exchange across cell boundaries. For example, the coast of England and Wales is divided into approximately eleven major sediment cells.

沉积物单元又称滨岸单元，是一个具有明确边界的相对独立的海岸分区。在单元内部，沉积物在波浪和洋流作用下从来源区经搬运区到达汇区，而跨单元边界的交换相对较少。例如，英格兰和威尔士海岸被划分为约十一个主要沉积物单元。

This concept is crucial for coastal management. If a harbour or sea wall interrupts longshore drift within one cell, down-drift beaches may be starved of sediment and erode rapidly. Management decisions must therefore be made at the scale of the whole sediment cell, not just at local hotspots.

这一概念对海岸管理至关重要。如果港口或海堤在某一单元内阻断了沿岸漂移，下风方向的海滩可能因缺少沉积物补充而迅速侵蚀。因此，管理决策必须在整个沉积物单元的尺度上做出，而不能仅在局部热点地区进行。

5. Marine Erosion Processes | 海洋侵蚀过程

Erosion at the coast occurs through several mechanical and chemical processes. Hydraulic action involves air being trapped and compressed in rock cracks; as waves retreat, the sudden pressure release causes the rock to weaken and shatter. Corrasion, or abrasion, occurs when waves hurl sand and pebbles against the cliff face, wearing it down like sandpaper. Attrition is the collision of sediment particles with one another, making them smaller and rounder. Solution, or corrosion, is the chemical dissolution of rocks such as limestone or chalk by seawater. Finally, wave pounding generates high pressures that can directly fracture the cliff.

海岸侵蚀通过多种机械和化学过程发生。水力作用是指空气被困在岩石裂缝中并被压缩；当波浪后退时，压力的突然释放导致岩石变弱碎裂。磨蚀作用（即研磨）是指波浪把沙子和砾石抛向崖面，像砂纸一样将其磨损。磨圆作用是指沉积物颗粒相互碰撞，使其变小变圆。溶液作用（即溶蚀）是指海水对石灰岩或白垩等岩石的化学溶解。最后，波浪冲击产生高压，可直接使悬崖破裂。

6. Marine Transport and Deposition | 海洋搬运与沉积

Longshore drift is the primary mechanism of sediment transport along a coast. Waves approach the beach at an oblique angle, carrying sediment up the beach in a swash; the backwash then flows straight down the beach under gravity. This zigzag movement transfers sediment progressively along the shoreline. Longshore currents, driven by wave refraction and breaking angles, reinforce this movement.

沿岸漂移是沉积物沿海岸搬运的主要机制。波浪以斜角接近海滩，通过涌升把沉积物带上海滩；回流则在重力作用下沿垂直方向流回。这种之字形运动使沉积物沿滨线不断向前搬运。由波浪折射和破碎角度驱动的沿岸流也加强了这种运动。

Deposition occurs when wave energy decreases, for example in sheltered bays or where the coastline changes direction. Onshore winds may carry sand landward to form dunes, while rivers and currents deposit fine silt in estuaries and mudflats. The balance between erosion, transport, and deposition is known as the sediment budget; a negative budget means net erosion, while a positive budget means net accretion.

当波浪能量降低时，例如在避风的海湾或海岸线改变方向的地方，就会发生沉积。向岸风可把沙子搬运到陆地形成沙丘，河流和洋流则在河口和滩涂沉积细粒粉砂。侵蚀、搬运与沉积之间的平衡被称为沉积物收支；负收支意味着净侵蚀，正收支意味着净淤积。

7. Landforms of Erosion | 侵蚀地貌

Erosional landforms develop along coasts with resistant rocks and high wave energy. Headlands and bays form when alternating bands of hard and soft rock are eroded at different rates; the soft rock retreats to form a bay, while the hard rock remains as a headland. Wave refraction concentrates energy on headlands and reduces energy in bays, reinforcing the pattern.

侵蚀地貌发育在岩性坚硬且波浪能高的海岸。海岬与海湾由软硬相间的岩层以不同速率侵蚀而成；软岩后退形成海湾，硬岩残留为海岬。波浪折射把能量集中在海岬上，在海湾中能量减弱，从而强化了这一格局。

On a headland, erosion exploits joints and faults to form cracks, then caves, then arches. When the roof of an arch collapses, it leaves a stack; further erosion reduces the stack to a stump. Cliff profiles are shaped by undercutting at the base, creating a wave-cut notch, followed by collapse and the development of a wave-cut platform at low tide. Blowholes may form where erosion opens a vertical shaft from a cave to the cliff top.

在海岬上，侵蚀沿节理和断层扩展，依次形成裂缝、洞穴和拱门。当拱门顶部崩塌后，留下海蚀柱；进一步侵蚀使海蚀柱变为海蚀残丘。悬崖剖面受底部掏蚀影响，形成波蚀龛，随后发生崩塌并发育出低潮时出露的波切台。当侵蚀从洞穴向上打开一个垂直通道直达崖顶时，就可能形成吹穴。

8. Landforms of Deposition | 沉积地貌

Depositional landforms occur where sediment supply exceeds removal. Beaches are the most common depositional landforms, composed of sand, gravel, or shingle; their profile and composition reflect the balance of constructive and destructive wave energy. Sand dunes form where strong onshore winds transport dry sand inland; vegetation such as marram grass traps the sand and stabilises successive dune ridges.

沉积地貌出现在沉积物供给超过移除的地方。海滩是最常见的沉积地貌，由沙、砾石或卵石组成；其剖面和成分反映了建设性与破坏性波浪能量的平衡。沙丘形成于强向岸风把干燥沙子向内陆搬运的地方；滨草等植被固定沙粒，使一道道沙丘脊逐渐稳定下来。

Spits are elongated accumulations of sand or shingle that extend from a headland across the mouth of a bay or estuary. They form where longshore drift deposits sediment in deeper water; their end often hooks landward due to wave refraction or secondary currents. A bar is a ridge of sediment that connects two areas of land or encloses a lagoon; a tombolo connects an island to the mainland, such as Chesil Beach in Dorset connecting the Isle of Portland to the English mainland. Offshore bars and barrier islands form parallel to the coast and protect it from wave attack.

沙嘴是从海岬向海湾或河口延伸的带状沙或砾石堆积体。它们形成于沿岸漂移在较深水中沉积物质，其末端常因波浪折射或次级海流而向陆弯折。沙坝是连接两块陆地或围成泻湖的沉积物脊；陆连岛把岛屿与大陆相连，例如多塞特的切瑟尔海滩把波特兰岛与英格兰本土连接起来。近岸沙坝和障壁岛平行于海岸线形成，并为海岸提供波浪保护。

9. Coastal Vegetation and Succession | 海岸植被与演替

Vegetation plays a vital role in stabilising depositional coastlines. On salt marshes, pioneer species such as glasswort colonise intertidal mud, slowing tidal currents and trapping fine sediment; as the marsh surface rises, less salt-tolerant plants replace them, illustrating a natural succession known as a halosere. On sand dunes, a similar succession called a psammosere runs from embryo dunes, through foredunes and yellow dunes, to grey dunes and finally scrubland.

植被在稳定沉积型海岸线中起着至关重要的作用。在盐沼中，碱蓬等先锋植物在潮间带泥滩定殖，减缓潮流并拦截细粒沉积物；随着沼泽地面升高，耐盐性较弱的植物取代它们，这展示了被称为盐生演替的自然演替序列。在沙丘上，类似的沙生演替从原始沙丘开始，经过前沙丘、黄沙丘、灰沙丘，最终发展为灌丛地。

Vegetation increases surface roughness, reduces sediment mobility, and promotes soil development, thereby creating a negative feedback loop that further stabilises the landform. However, human trampling and vehicle use can break this plant cover, exposing dunes or marshes to severe deflation and erosion.

植被增加了地表粗糙度，降低了沉积物的流动性，并促进土壤发育，从而形成一种负反馈回路，使地貌更加稳定。然而，人类践踏和车辆使用会破坏这种植被覆盖，使沙丘或沼泽暴露于严重的风蚀和水蚀之中。

10. Human Activity and System Feedback | 人类活动与系统反馈

Human activity alters coastal systems by modifying energy and sediment flows. Hard engineering structures such as groynes trap sediment on the up-drift side but starve the down-drift side, causing severe beach erosion. Sea walls reflect wave energy, sometimes increasing scour at their base. Dams and river management reduce the sediment supply reaching the coast, leading to negative sediment budgets and increased erosion. Conversely, beach nourishment artificially adds sediment to the system, while managed retreat allows controlled flooding and encourages natural sediment accumulation.

人类活动通过改变能量和沉积物流来影响海岸系统。丁坝等硬性工程结构在迎风侧拦截沉积物，却使背风侧缺沙，造成严重的海滩侵蚀。海堤反射波浪能量，有时加剧堤脚冲刷。大坝和河流管理减少了到达海岸的沉积物供给，导致沉积物收支为负和侵蚀加剧。相反，海滩补沙人为地向系统添加沉积物，而退田还海则允许受控淹没并促进自然淤积。

These interventions create positive and negative feedback loops. For example, building a sea wall reduces cliff erosion, which removes a sediment source; down-drift beaches then erode, encouraging yet more defensive structures. This illustrates the importance of integrated coastal zone management at the scale of the sediment cell.

这些干预会产生正反馈和负反馈回路。例如，修建海堤减少了悬崖侵蚀，从而消除了一个沉积物来源；随后下游海滩发生侵蚀，又促使人们建造更多的防护设施。这说明了在沉积物单元尺度上进行海岸带综合管理的重要性。

11. Case Example: Coastal Management and Systems Thinking | 案例：海岸管理与系统思维

A well-known example is the Holderness coast in eastern England, one of the fastest-eroding coastlines in Europe. Soft glacial till cliffs retreat by up to 2 metres per year. Defences placed at some settlements have trapped sediment updrift, but this has accelerated erosion for communities to the south, such as Mappleton and Great Cowden, highlighting the connectivity of the sediment cell.

一个著名案例是英格兰东部的霍尔德内斯海岸，这是欧洲侵蚀最快的海岸线之一。柔软的冰碛物悬崖每年后退可达2米。一些居民点设置的防护设施在漂移上游拦截了沉积物，但加剧了南侧社区（如梅普尔顿和大考登）的侵蚀，这凸显了沉积物单元的连通性。

Geographers use sediment budgets and mapping of cell boundaries to predict which areas will gain or lose sediment. By treating the coast as an integrated system, sustainable management can prioritise soft engineering, managed realignment, and sediment recycling to maintain dynamic equilibrium. Ultimately, the coastal system concept reminds us that no intervention is purely local: every change ripples through the entire cell.

地理学家利用沉积物收支和单元边界制图来预测哪些区域会获得或失去沉积物。通过把海岸视为一个整体系统，可持续管理可以优先采用软性工程、有管理的重新调整和沉积物循环利用，以维持动态平衡。归根结底，海岸系统概念提醒我们，任何干预都不是纯粹局部的：每一个变化都会在整个单元中产生涟漪效应。

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Coastal Systems and Landscapes Overview | 海岸系统与景观概述