Introduction to Coastal Interactions

System Interactions Coastal Erosion

Introduction

In semi-arid regions, groundwater is an important source of water supply. Groundwater is protected  

from high evaporation that affects surface water bodies. Hence the sustainability of groundwater  

bodies are very important, and to increase the sustainable yield of a groundwater body, one of the main methods is induced groundwater recharge. Especially under the conditions of climate change, managed aquifer recharge systems can be more effective than increasing the capacity of the surface reservoir. It could also be the most economically and socially practical solution for the integrated management of water resources.  

A barrier called a recharge check dam is placed across a river or channel to slow the movement of water and to encourage groundwater recharge. 

Check dams 

Check dams are temporary or permanent structures. These are constructed around drainage systems ditches to manage stormwater runoff, avoid erosion, blocks sediments, and prevent them from passing through the dam. The construction of check dams is mostly done by using rocks, sediment holding fiber rolls, stones, sand, and gravel bags. Check dam reduces the velocity of runoff, avoids erosion, and ensures sedimentation. 

Check dams are created in already damaged areas, where natural or agricultural vegetation cover was lost or not capable of holding the topsoil. Normally they are built in areas hit by severe runoff actions, where standard erosion control methods are not enough.  

Check dams help in the removal of coarse and medium size sediment from runoff. But fine particles of silt and clay will pass through the spaces on these check dams. These are used for soil conservation, control of soil erosion, land development, and flood control.  

Dams interrupt the continuous flow of sediment transport through rivers, causing sediment to accumulate in the reservoir itself (damaging reservoir operation and decreasing storage). Due to human activity, increased loads of fine sediment, for example, from land disturbance, can cause problems such as increased turbidity in the water column and sedimentation in river channels, estuaries, harbors, and deposition of fine-grained sediment in streambed gravels can affect salmon habitat. 

Wetlands: 

Wetlands are areas where water covers the soil or water is present either at the surface of the soil or near the surface of the soil throughout the year or for varying periods of time throughout the year, including during the growing season.  

Saturation of water (hydrology) mainly defines the development of soil and the types of plants and animals living in and on the soil. Wetlands can support both aquatic (hydrophytes) and terrestrial (land) species. The continuous presence of water favor the growth of aquatic plants (hydrophytes) and helps in the development of characteristic wetland (hydric) soils. 

Types of wetlands 

Wetlands differ widely because of regional and local changes in soils, topography, climate, water, vegetation, and human disturbance. Actually, wetlands are present on every continent and from the tundra to the tropics except Antarctica. Two general types of wetlands are: coastal or tidal wetlands and inland or non-tidal wetlands. World wetland day is celebrated on 3^rd February. 

Coastal/Tidal Wetlands 

Coastal or tidal wetlands are found along the coasts. They are closely linked to estuaries where seawater mixes with freshwater to form an environment of variable salinities. The fluctuating water levels that are due to tidal action and the saltwater combine to create a difficult environment for many plants. Therefore, many shallow coastal areas are non-vegetated mudflats or sand flats. But some plants are successfully adapted to this natural environment. Some grasses and grass like plants that adapted to the salty conditions form the tidal salt marshes that are found along the coasts. In a tropical climate, mangrove swamps with salt-loving shrubs or trees are common. The formation of some of the tidal freshwater wetlands takes place beyond the upper edges of tidal salt marshes, where the influence of saltwater ends. 

Inland/Non-tidal Wetlands 

Inland or non-tidal wetlands are most common on floodplains besides rivers and streams in isolated depressions surrounded by dry land, along the boundaries of lakes and ponds, and in low-lying areas where the groundwater interrupts the soil surface or the area where precipitation sufficiently saturates the soil. Inland wetlands comprise of marshes and wet meadows that are dominated by herbaceous plants, swamps that are dominated by shrubs, and wooded swamps where many trees are present.  

Importance of Coastal wetlands: 

We get important services from coastal wetlands, such as food and biomaterials as direct resources, habitat for wildlife, carbon sequestration, protection against storm surges, and sediment accumulation for land accretion. Coastal wetlands also give water purification, tourism resorts, and other functionalities. 

Wetland disturbance and its impact: 

Types of Wetland Impacts 

Direct impacts: It result from the disturbances that arise in the wetland. Filling, grading, removal of vegetation, building construction and changes in water levels and drainage patterns are some of the common direct impacts of wetlands. Most disturbances that result in direct impacts to wetlands are regulated by the State and Federal wetland regulatory programs. 

Indirect impacts: It result from the disturbances that arise in outside areas of the wetland, like uplands, other wetlands. Influx of surface water and sediments, fragmentation of a wetland from a contiguous wetland complex, loss of recharge area, or changes in local drainage patterns are some of the common indirect impacts. Many indirect impacts are beyond the authority of State and Federal wetland regulatory programs. Hence, wetland protection can be given by a watershed management plan under local implementation. 

Cumulative impacts: These result from combination of direct and indirect impacts to the wetland over a period of time. 

Human impact on wetlands 

Many changes have been caused by human influences that lead to changes in the function and quality of wetlands. These changes have resulted from changes in the physical, chemical, and biological factors of wetland ecosystems. Extensive land development and clearing of land have resulted in increased erosion in highland areas leading to increased sedimentation in lowland wetlands. This increased accumulation of sediment can change the chemical and hydrologic system of the wetlands in a relatively short time. Other human activities that have long-lasting effects on wetland ecosystems comprise stream channelization, dam construction, discharge of industrial wastes and municipal sewage and runoff urban and agricultural areas (non-point source pollution). These activities have an impact on changes in the flood regime of wetlands and the input and cycling of nutrients.  

Local and regional effects on the chemistry and quality of water flowing through wetlands depend on the sources of pollution. Point sources, like municipal, industrial sites, and non-point sources, such as agricultural lands and urban runoff, add materials to groundwater and surface water that disturbs the balance of water chemistry in the wetland and the biogeochemical cycling of materials in wetland ecosystems. 

Natural impact on wetlands 

Rise in sea-level 

The gradual rise of sea level has the ability to both increase wetland area by periodically flooding low-lying uplands and to damage vegetated wetlands by increasing water depths. 

Coastal marshes and swamps are very susceptible to rising sea level because they are generally within a few feet of sea level. When the sea rises, the outer boundary of these wetlands erodes, and new wetlands form. The number of new wetlands will be much smaller than the area of wetlands that are lost. Near sandy beaches, like wetland shores, property owners often remove these structures to stop erosion. Even though these structures keep the property safe, they can destroy beaches, particularly bay beaches, which are usually less than 10 feet wide. Fishing, recreation, transportation, and landing small crafts are some of the uses of beaches in addition to their environmental importance in the evolution of coastal wetlands. Erosion threatens the high ocean sides of densely developed islands and is a more immediate problem than the flood of the low bay sides. Climate change also increases the chances of flooding and erosion in coastal areas. A higher sea level increases the flood level from a storm of a given severity. Wetland loss and degradation is a major problem, as it adds to global warming by converting these natural carbon sinks into emission sources. 

Climate Implications – Wetlands 

Effects of climate changes like drought, warmer temperatures and changing precipitation patterns can all affect the health and useful functionality of wetlands. Sea level rise and wildfires can affect wetlands, where climate changes are happening. Climate changes, in combination with other factors such as land development, may further worsen the loss of wetlands.  

Warmer temperatures, drought, and changes in the pattern of precipitation can increase evapotranspiration and lead to loss of water. Drought can also cause incidents such as wildfires that can alter the quality of water, watershed, and the structure and function of wetlands. Wetland’s loss led to reduced fish wildlife habitat and worsened present shifts in species ranges.  

Some coastal wetland types may be in danger to climate change, including salt marshes, bottomland hardwood swamps, fresh marshes, mangrove swamps, and shrubby depressions. Tidal and non-tidal wetlands may be at threat from sea-level rise. Sea-level rise may bring saltwater into non-tidal wetlands, which can be inhibited from moving inland due to coastal development. Climate change can reduce the ability of sediment accumulation in tidal wetlands leading to the drowning of vegetation. 

Summary

• In semi-arid regions ,ground water is an important source of supply.
• A wetland is an area of land that is either covered with water or filled with water.
• Two general types of wetlands are costal or tidal wetlands and inland or non tidal wwetlands.
• Coastal or tidal wetlands are found along the coasts.
  Inland wetlands are comprised of marshes and wet meadows that are dominated by herbaceous plants and swamps.
• Filling, grading, removal of vegetation, building construction and changes in water levels and drainage patterns are some of the common direct impacts of wetlands.
• Indirect impacts result from disturbances that arise in outside areas of the wetland, like uplands other wetlands.
• Cumulative impacts result from a combination of direct and indirect impacts to the wetland over a period of time.
• Changes caused by human influences leads to changes in the function and quality of wetlands.
• Coastal marshes and swamps are very susceptible to rising sea levels.