Educational Visit to Dhom Dam, Wai

The visit to dam site was organised with the intention to have a practical experience of the theoretical knowledge of Dams and Hydraulics. The practical experience to dam site made me understand every minute specification and detailing done while operating a dam. 

The Dhom dam is located on river krishna near dhom village in wai taluka. The main purpose for setting up the dam was for Irrigation purpose. Dhom village is situated at a distance of 37.9 km from Satara city and 7.9 km from Wai. Dhom has epithetic name "Dakshin Kashi" and in old times it was known as "Virat Nagari". The Dhom dam is Earthen/ Gravity Masonry dam.

Specifications of Dam

Sr.no	Attribute	Value
1	Name of dam	Dhom Dam
2	Operating and Maintenance agency	WRD,GOM
3	Seismic Zone	Seismic zone IV
4	Type of Dam	Earthen/ Gravity Masonry
5	Total Height of dam above Foundation	50m
6	Total Volume Content of Dam ( TCM)	6335
7	Design Flood (cumec)	2066
8	Type of Spillway	Ogee
9	Length of Spillway (m)	71
10	Crest level of Spillway (m)	741
11	Spillway capacity (cumec)	1178.29
12	Type of Spillway Gates	Radial
13	No of Spillway Gates	5
14	Size of Spillway gates (m x m)	12 x 6.5

Monitoring & Inspection of Dam.

Inspection of dam plays a very important role on dam site. Inspection are a necessary part of owning and operating a dam since early detection of gradual changes can minimize problems and reduce maintenance costs. Therefore Inspections are made daily, monthly and annually according to the need. Routine inspections are also an opportunity to note any vandalism which may have occurred.

1. Daily/ weekly Inspections- In this part the inspection of river flow observations, precipitation records, water level readings, gate operation, seepage monitoring (if present) is done.
2. Monthly Inspections-  In this part inspection of  operating equipment, safety equipment, performance and super-facial structure is done.
3. Annual Inspections- In this part the irrigation of Structural part and operating unit is done.
4. Detailed Inspections - In this part the detailed survey is conducted by Department of Natural Resources.

Ogee Spillway & Stilling Basin.

A spillway is a structure used to provide the controlled release flow from dams or leave into a down stream.Spillways release the extra water from the dam which helps the dam to maintain its stability and to avoid the flood or failure of dam.

In Dhom dam the ogee spillway was provided to pass the excess of water from dam. The chute spillway is however most common and basic design which transfers the excess water from upstream face to downstream face in control and smooth manner. These are usually design from ogee curve most often they are lined on the bottom and side with concrete to protect the dam and topography.

When the water in reservoir is above its capacity the gates of dam are opened and the excess water is outlet to the downstream side, however at the time of discharge huge energy is been created  which is dangerous of scour to the riverbed which may threaten the stability of dam and the neighboring river valley slopes and also the villages located on downstream sides. Therefore stilling basin is constructed on the downstream toe of spillway also know as energy dissipators which helps to absorb or cut the high amount of energy produced.

Gates

The gates are provided on dam site to lock the force of river water and to collect the water from seasonal rivers which can be used at the time of summers to nearby areas for various means. The Radial gates were provided at dhom dam. There were 5 gates of size 12 x 6.5 m. This gates were operated electrically as well as manually too. 

The manual operation for gate was set up with bad experience of electric motor failure at the time of heavy discharge of water in past. Therefore the manual operation of gates was also provided for dam to avoid such conditions which affects the stability of dam. The emergency gates were also provided on dam which are used at time of maintenance and repair of regular gates.

Cross Sections of Dam

Canals Provide

There were two canals provided from Dhom dam both transfers the dam water to various taluka's of Satara district for successful operation of irrigation purpose. The Right and Left canal were provided from dhom dam. 

Right canal was provided for a distance of 113 km from dhom dam to various taluka's of Satara district. The capacity of right canal is 230 cumec.

left canal was provided for a distance of 166 km from dhom dam to various taluka's of satara district. The capacity of left canal is 750 cumec.

Photos at Dam Site

Study of Waste-Water Treatment Plant

Waste-water relates to output source of water which we get from several activities like bathing, washing, using the toilet, outsource water from industries, rainwater runoff etc. Waste-water treatment is the process of converting the water that is no longer useful for human activities into the bilge water that can be discharged back to environment. Waste water contains all sorts of bacteria, chemicals and toxic elements which are very harmful to discharge directly in the atmosphere therefore the waste-water treatment is been brought into action so as to reduce the contaminants to acceptable level to make water safe to discharge in environment.

There are two forms of waste water treatment plants which depend upon the effluent that is to be treated. The two types of waste water treatment plants are chemical or physical treatment plant & biological treatment plant. Biological waste treatment plants use biological matter and bacteria to break down waste matter whereas physical waste water treatment plants use chemicals and physical process to treat waste water. Biological treatment systems are ideal for treating waste water from households and business premises. Physical waste water treatment are used to treat waste water from industries, manufacturing firms and factories since these firms produce waste water containing toxic chemicals which are hazardous to discharge.

Simple Waste water Treatment Process Diagram.

Procedure of Waste-water Treatment Plant

The following is the step by step process for treating the waste water

Step 1- Waste Water Collection.

This is the first step of any plant to collect the waste water from every part of city. The waste water from buildings, malls, public offices and any other source of waste water is been collected with help of drainage underground pipes at one point and then send to treatment plant.

Drainage Pipes.

Step 2-  Odour Control.

This step plays an important role at treatment plant. The waste water contains various unwanted materials which results in anaerobic or septic conditions. This condition takes place when there is limited flow of oxygen or no dissolved oxygen available for respiration of microbes in waste water. This allows microbes to emerge as an "sulphate reducing bacteria" to thrive. These bacteria use sulphate ion and gives byproduct as hydrogen sulphate (H2S) which smells like rotten egg.

There are many different types of technologies to control odour from waste water collection and treatment systems. The two technologies used are liquid-phase and  vapour-phase technology. The liquid- phase technology is used where both corrosion and odour are concern whereas the vapour-phase technology is used to control odour in air and gas, usually they are used in point-source applications.

Step 3 - Screening.

The next process is of screening where the unwanted floating material is been separated from waste water. The waste water is passed through the screens and floating unwanted materials is been removed. there are three types of screens used  coarse, medium & fine.

1. Coarse screen has larger openings from 75- 150 mm.
2. Medium screens has opening from 20-50mm.
3. Fine screens have openings less than 20mm.

Grit Chamber- The waste water is then passed through grit chamber where the inorganic materials like sand, ash etc are removed. Basically the sedimentation process is been carried out in this part.

Skimming Tanks-  There are chances of having greasy and oily elements in waste water from industries and manufacturing firm outlets. Thus skimming tanks helps to remove this unwanted materials form waste water. The skimming tank is surrounded by baffle walls and the compressed air is been flushed inside from the floor of skimming walls and the rising air bubbles coagulates and solidify these materials and these material are then pushed to side compartment from where these elements are easily removed.

Step 4-  Primary Treatment.

The unwanted materials which are not removed from previous material are removed in this step by application of sedimentation process. The unwanted materials remains in suspended state in flowing water, however when this flowing waste water is stopped and stored in tank called sedimentation tank
then this matter gets settled down due to action of gravity after a certain amount of time. Sometimes the coagulants are used to facilitate the sedimentation process & then this process is called as coagulation- aided sedimentation. 

The process of sedimentation depends upon some factors like size, shape & specific gravity of particles besides viscosity and flow velocity of  waste-water. In normal process of treatment, sedimentation is usually carried out twice-once before the secondary treatment, referred to as primary sedimentation and after this process the secondary sedimentation is brought to action.

Coagulants: These are chemicals usually positively charged & which form insoluble & gelatinous precipitates with colloidal particles which are negatively charged which are present in waste water and thus this particles become denser and due to gravity action they gets settled down at bottom of sedimentation tank. The most common used coagulants in treatment process are alum (aluminium sulphate), iron salts (ferric sulphate, ferric chloride), lime and soda ash (sodium carbonate), sodium silicate & sodium aluminate.

Step 5- Secondary Treatment. 

This process is also known as activated sludge process. The secondary treatment process involves adding seed sludge to waste water to ensure that it is broken down further. Air is first pumped into huge aeration tank which mix the waste water with seed sludge which is basically small amount of sludge, which fuels the growth of bacteria which uses oxygen and other microbes that consumes the remaining organic matter. This process leads to the production of large particles  that settle down in huge tanks. The waste water passes through large tanks for a period of 3-6 hours. 

Some secondary treatment methods include a secondary clarifier to settle out and the biological floc or filter material grown in  the secondary treatment bioreactor. Some alternative methods are activated sludge, aerated lagoon, aerobic granulation, constructed wetland, membrane bioreactor, rotating biological contactor, trickling filter.

• Activated Sludge - It is the process of treating sewage and industrial waste waters using air and biological floc composed of bacteria and protozoa.
• Aerated Lagoon - It is a holding or treatment pond provided with artificial aeration to promote the biological oxidation of waste water. There are many other biological process for waste water treatment for example trickling filters, rotating biological contactors & biofilters.
• Aerobic Granulation - The biological waste water treatment is often accomplished using conventional activated sludge systems. These systems generally require large surface area for treatments and biomass separation units due to generally poor settling properties of the sludge.

Step 6- Tertiary Treatment.

This stage is similar to those used in water treatment plant which clean raw water for drinking purposes. The treatment Stage has the ability to remove up to 99% of the impurities from waster water. This produces effluent water that is close to drinking water quality. Unfortunately this process tends to be costly as it requires special equipments, well trained and highly skilled operators.

Step 7 - Disinfection. 

In this process the waste water treated from primary and secondary treatment contains some harmful elements which are to be removed so the disinfection process is been brought to action. The waste water is kept in tank known as disinfection  tank which contains chlorine and hypo chlorine present in it which helps to remove the unwanted materials and keep water to acceptable limit for a long time span. The waste water is kept in disinfection tank for nearly 30 min. The UV rays method is also applicable but its to costly therefore the chlorination process is more popular.

Step 8 - Sludge Treatment.

The sludge that is collected during primary and secondary treatment requires concentration and thickening to enable further processing. It is put in to thickening tanks that allow it to settle down & later separate from water this requires a time span of around 24 hours. The remaining water is collected and send back to aeration tank for further treatment. The sludge collected and be used in agriculture lands as manure.