Understanding a watershed
To understand any watershed , First of all it is important to understand the watershed ecology. Watershed ecology emphasize on structural and functional characteristics of watershed and signifies the influence of these characteristics on coexistence of human and natural communities. There are 5 elements of watershed ecology :
1. Physical System- The physical system covers the physical processes which are shaping forces of ecosystems. Climate, hydrology, and geomorphology are the sub elements of physical system upon which all life is ultimately based.
The basic elements of physical system includes –
a)Climatic
b) Geomorphic processes, and
c) Hydrologic processes
The Climate, its science and its causes, becomes important in understanding regional issues in watershed science. climate is actually a distinct term with important ecological ramifications. It refers to an aggregate of both average and extreme conditions of temperature, humidity, and precipitation (including type and amount), winds, and cloud cover, measured over an extended period of time. Climate heavily influences watershed vegetation communities, stream flow magnitude and timing, water temperature, and many other key watershed characteristics.
Geomorphology, however, refers specifically to the study of the landforms on the earth and the processes that change them over time. It helps to explain river and watershed forms. Fluvial geomorphology, referring to structure and dynamics of stream and river corridors, is especially important to understanding the formation and alteration of the stream or river channel as well as the flood plain and associated upland transitional zone; this is a critical discipline for effective, long-term watershed management.
Hydrology is the science of water, as it relates to the hydrologic cycle. More specifically, it is the science of water in all its forms (liquid, gas, and solid) on, in and over the land areas of the earth, including its distribution, circulation and behavior, its chemical and physical properties, together with the reaction of the environment (including all living things) on water itself. Further, the global water budget adds further insight into the water resources of our planet.
These three elements of the physical system along with other factors also interact significantly in determining the structure and composition of a watershed and its biotic communities. As a result of different combinations of these formative processes, different types of watersheds are created. Here are some examples that show how different from one another watersheds of different origin and physical template conditions can be.
2. The Biological system- This biological ecosystem is associated with bio ecosystem science and relates to living plant and animal communities. The biological system describes the biological setting of watersheds and the interactions of biotic components of the biological system with the basic elements of physical system. It is important to have a working knowledge bio -ecological phenomena like ecology, species, population, community, habitat, niche, ecosystem, ecotone, biosphere .Beyond these basic definitions it is equally important to understand the bio-ecological concepts and its relevance to watershed
3. Natural systems- The watersheds is surrounded with natural system . Watershed is a part of existing natural system .it describes how different-sized watersheds operate on various spatial and temporal scales. The natural ecosystem of watershed further introduces two vital concepts i.e structure and function for understanding and managing watersheds and ecosystems.
It is the existing physical system(climate , geomorphology, Hydrology) from which watershed develops .The biological setting of the biological system then becomes established upon and integrated with the physical system. The interactions of Physical and biological system in the natural system of watershed links the abiotic and biotic components of watersheds and forms system-like behavior. This whole system consists of group of interrelated, interacting, or interdependent constituents that in turns forms a complex whole. These interacting components together perform the work like transport sediment, water, and energy and in due course of interactions generate outputs in the form of new physical structures like floodplains or channels, and form biological communities and new energy outputs).In this existing natural system, each of the physical and biological components of watersheds if they existed separately would not be capable of generating the work and the products that the intact watershed system can generate. The interaction of physical and biological system in existing natural system of watersheds is key to watershed management. It further emphasizes that the tentacles of a watershed, as a natural system, is more than just a varieties of natural resources occurring in one place. Thus it is clear that recognizing the natural system and working toward protecting the system’s critical components and functions are key to sustainable watershed management.
4. Watershed structure- It includes various patterns of physical structure formed by both the living and non-living watershed components. Basically, this includes structure of flowing waters (mainly rivers and streams with associated riverine wetlands and riparian zones), still waters (lakes and associated basin-type wetlands and shore lands), and upland areas of watersheds.
5. Watershed functions- It covers the watershed functions and processes i.e vital cyclic events necessary to the continuation of life in aquatic and terrestrial systems. As discussed earlier ,The interacting components of physical and biological components in a natural system in watershed together perform the work like transport sediment, water, and energy and in due course of interactions generate outputs in the form of new physical structures like floodplains or channels, and form biological communities and new energy outputs).So, how watersheds as natural systems are capable of performing many complex functions. Of many functions , the 2 main functions are:-
A. Transport and storage
B. Cycling and Transformation.
A. Transport and storage
a) Transport and storage of water:
Even before precipitation reaches the ground ,it interacts with vegetation. Trees and other vegetation are responsible for interception and detention of some of the rainfall, leading to some evaporation and also slowing the amount reaching the ground via through fall and giving it time for better infiltration to groundwater (one form of storage). Saturation of soils, occurring when precipitation exceeds infiltration, leads to overland flow and, over longer time frames, drainage network development. The consistent flow of water in channels affects and shapes channel development and morphology in ways that seek dynamic equilibrium with the job to be done (moving water downstream).
b).Transport and storage of sediments.
watershed is an area that drains to a common body of water, one of its main functions is to temporarily store and transport water from the land surface to the water body and ultimately (for most watersheds) onward to the ocean. But, in addition to moving the water, watersheds and their water bodies also transport sediment Watersheds also collect and transport sediments as a major function. Sediment transport and storage is a complex network of smaller watershed processes, like the water processes described above, and actually is inseparable from water transport and storage. Sediment related processes mostly involve erosion and deposition, but sediment transport and storage also play a longer-term role in soil development. The drainage network development and channel development. The redeposition of sediments on floodplains is an important function that rejuvenates soils and influences the productivity and diversity of stream corridor ecosystems.
B. Cycling and Transformation.
Like transport and storage ,Cycling and transformation are also natural functions in watersheds. Cycling involves an element of interest’s transport and storage, change in form, chemical transformation and adsorption. In the natural system of watershed, many elements and materials (including water) are in constant cycle through watersheds. The interactions of these elements and materials drive countless other watershed functions. Interactions of the carbon and nitrogen cycles with stream biota results in influence on dissolved oxygen. Elements like carbon, nitrogen, and phosphorus leads to bio geochemical cycles.
