Unit 3
Environmental and Water Resource Engineering
Water demands
System water demand is the quantity of water that the treatment plant must produce in order to meet all water needs in the community. Additionally, virtually all systems have a certain amount of leakage that cannot be economically removed and thus total demand typically includes some leakage.
Water demands can be classified into:
- Domestic Water Demand.
- Industrial Water Demand.
- Institutional
- Commercial Water Demand.
Design period
The design period may be defined as. It is the number of years in the future for which the given facility is available to meet the demand. Or. The number of years in the future for which supply will be more than demand.
Per Capita Demand
The quantity of water required for municipal uses for which the water supply scheme has to be designed requires the following data: Water consumption rate (Per Capita Demand in liters per day per head) Population to be served. Overall, the average total demand is about 680 liters (180 gallons) per capita per day, when commercial and industrial water uses are included.
Forecasting of Population: 9 Methods are:
- Arithmetical Increase Method
- Geometrical Increase Method
- Incremental Increase Method
- Decrease Rate of Growth Method or Decreasing Rate Method
- Simple Graphical Method
- Comparative Graphical Method
- The Master Plan Method or Zoning Method
- Logistic Curve Method
- The apportionment method
Arithmetical Increase Method:
This method is based on the assumption that the population is increasing at a constant rate. The rate of change of population with time is constant.
i.e. dp/dt = C (a constant)
Integrating P2-P1 = C(t2-t1)……………..(5.5)
Where P1 = Population at the time t1 first census
P2 = Population at the time t2 last available census
The value of constant C is determined.
Now the population after n decade can be determined by the formula
Pn = P + n. C
Geometrical Increase Method:
This method is based on the assumption that the percentage increase in population from decade to decade remains constant. In this method the average percentage of growth of the last few decades is determined; the population forecasting is done on the basis that the percentage increase per decade will be the same. If the present population is P and the average percentage growth is IG the population at the end of n decade will be:
Incremental Increase Method:
This method is an improvement over the above two methods. The average increase in the population is determined by the arithmetical method and to this is added the average of the net incremental increase once for each future decade.
P is the present population, la = Average Arithmetical increase, and lC is the average incremental increase, then population after ‘n’ decade will be
Pn = P + n (la + Ic)
Functions of each unit
- Intake well the raw water is admitted from the source, in these wells, through the inlet opening having a screen to separate the floating material.
- The screen is used to remove the floating, suspended material.
- Aerators To remove the gases from the water, the raw water is exposed to the air.
- Coagulant tank It is Used to add the coagulant into the water.
- Flash mixer in this unit, added coagulators are properly mixed.
- Clari Floccurator in this unit two processes are done i.e. Flocculation and sedimentation.
- Flocculation Floc is formed and in sedimentation, Floc gets settled down.
- Filter beds It helps to remove the fine and colloidal matter from the water.
- Disinfection It helps to kill microorganisms and also to destroy organic impurities. This is an important process for water treatment.
- Distribution System Treated water convey to the household.
Watershed management - Definition, Necessity, and methods
Definition
Watershed management is a term used to describe the process of implementing land-use practices and water management practices to protect and improve the quality of the water and other natural resources within a watershed by managing the use of those land and water resources in a comprehensive manner.
Necessity
Runoff from rainwater or snowmelt can contribute significant amounts of pollution into the lake or river. Watershed management helps to control pollution of the water and other natural resources in the watershed by identifying the different kinds of pollution present in the watershed and how those pollutants are transported, and recommending ways to reduce or eliminate those pollution sources.
All activities that occur within a watershed will somehow affect the watershed’s natural resources and water quality. New land development, runoff from already-developed areas, agricultural activities, and household activities such as gardening/lawn care, septic system use/maintenance, water diversion, and car maintenance all can affect the quality of the resources within a watershed. Watershed management planning comprehensively identifies those activities that affect the health of the watershed and makes recommendations to properly address them so that adverse impacts from pollution are reduced.
Watershed management is also important because the planning process results in a partnership among all affected parties in the watershed. That partnership is essential to the successful management of the land and water resources in the watershed since all partners have a stake in the health of the watershed. It is also an efficient way to prioritize the implementation of watershed management plans in times when resources may be limited.
Because watershed boundaries do not coincide with political boundaries, the actions of adjacent municipalities upstream can have as much of an impact on the downstream municipality’s land and water resources as those actions carried out locally. Impacts from upstream sources can sometimes undermine the efforts of downstream municipalities to control pollution. Comprehensive planning for the resources within the entire watershed, with participation and commitment from all municipalities in the watershed, is critical to protecting the health of the watershed’s resources.
- To improve the groundwater level, several civil structures are constructed in the watershed area, pits, and trenches.
- The pits or trenches are dogged at equal intervals on the skipping surface to cut the surface – flow and to allow it to percolate through these trenches to enrich the ground level.
- Stone embankment or earthen dams.
- They are constructed to check the surface – runoff in the catchment areas, to enrich the groundwater.
- The farm pond.
- They are constructed near the agriculture field in the catchment area to provide enough surface water to the field and also to enrich the groundwater.
- Dykes or underground barriers.
- These structures are constructed in the small surface streams e.g. The nallahs, to prevent the free groundwater flow and allow the water-table to come up, to help to improve the irrigation through the dug – wells.
Rainwater harvesting systems
Rainwater harvesting is the simple process or technology used to conserve Rainwater by collecting, storing, conveying, and purifying Rainwater that runs off from rooftops, parks, roads, open grounds, etc. for later use.
Rainwater harvesting systems consists of the following components:
- Catchment- Used to collect and store the captured Rainwater.
- Conveyance system – It is used to transport the harvested water from the catchment to the recharge zone.
- Flush- It is used to flush out the first spell of rain.
- Filter – Used for filtering the collected Rainwater and remove pollutants.
- Tanks and the recharge structures: Used to store the filtered water which is ready to use.
The process of rainwater harvesting involves the collection and storage of rainwater with the help of artificially designed systems that run off naturally or man-made catchment areas like- the rooftop, compounds, rock surface, hill slopes, artificially repaired impervious or semi-pervious land surface.
Several factors play a vital role in the amount of water harvested. Some of these factors are:
- The quantum of runoff
- Features of the catchments
- Impact on the environment
- Availability of the technology
- The capacity of the storage tanks
- Types of the roof, its slope, and its materials
- The frequency, quantity, and quality of the rainfall
- The speed and ease with which the Rainwater penetrates through the subsoil to recharge the groundwater.
The rainwater harvesting system is one of the best methods practiced and followed to support the conservation of water. Today, scarcity of good quality water has become a significant cause of concern. However, Rainwater, which is pure and of good quality, can be used for irrigation, washing, cleaning, bathing, cooking, and also for other livestock requirements.
The benefits of the rainwater harvesting system are listed below.
- Less cost.
- Helps in reducing the water bill.
- Decreases water demand.
- Reduces the need for imported water.
- Promotes both water and energy conservation.
- Improves the quality and quantity of groundwater.
- Does not require a filtration system for landscape irrigation.
- This technology is relatively simple, easy to install, and operate.
- It reduces soil erosion, stormwater runoff, flooding, and pollution of surface water with fertilizers, pesticides, metals, and other sediments.
- It is an excellent source of water for landscape irrigation with no chemicals and dissolved salts and free from all minerals.
Irrigation may be defined as the science of the artificial application of water to the land in order to fulfill the water requirements of the crops throughout the crop period for the full nourishment of the crops. Nutrients to the crops may also be applied through irrigation.
Necessity of irrigation
Water is necessary for plant growth and maturity. It is not always possible to get water from natural means. Irrigation, the artificial means of supplying water, becomes important for plant growth in the following cases.
If rainfall is less than the demand for plants, irrigation is necessary to fulfill the water requirement of plants.
The difference in water holding capacity of the soil plays an important role in the Necessity of Irrigation supply. For example, sandy soil requires frequent irrigation than clay soil.
If rainfall is sufficient but spatial distribution is not as per requirement, irrigation becomes necessary.
If rainfall is sufficient, spatial distribution is also good but temporal distribution is not as per requirement, irrigation water is necessary for plants.
Benefits of irrigation
- Agriculture is often greatly hampered due to irregular, insufficient, or uncertain rain. Proper irrigation systems can secure uninterrupted agriculture.
- The productivity of irrigated land is more than the un-irrigated land. Crop yields everywhere in the developing world are consistently higher in irrigated areas than in rainfed areas.
- Seeds cannot grow in dry soil as moisture is necessary for the germination of seeds. With the help of irrigation supply, the required moisture content of soil for the growth of seed can be ensured.
- Multiple cropping in a year is possible through irrigation. This will enhance production & productivity. In many areas of India, two or three crops in a year are cultivated with irrigation facilities.
- Through irrigation, it is possible to supply the required amount of hydrogen & oxygen, which is important for the proper development of plant roots.
- A plant can absorb mineral nutrients from the irrigated soil. Thus irrigation is essential for the general growth of the plant.
- Bringing more land under cultivation is possible through irrigation.
- Insufficient rain may also cause drought & famines. Irrigation can play a protective role during the period of drought & famines.
- Irrigation contributes to the economic growth and poverty reduction2. As income and employment are closely related to output and irrigation increases production, a substantial increase in income is achieved in the countryside.
Reference Books
- A Text-Book of Building Materials, by C.J. Kulkarrni
- Building Materials, by P. C. Varghese
- Building Construction, by P. C. Varghese
