GUIDELINES FOR SMALL HYDRO POWER PLANTS PLANNING
Many people have access to some form of running water and do not know how much power, if any, can be produced from it. Almost any house site has solar electric potential (photovoltaic). Many sites also have some wind power available. But water power depends on more than the presence of water alone. A lake or well has no power potential. The water must be flowing. In construction of small or micro hydro system many factors determine the feasibility of such a system. These include:
the amount of power available from the stream, and if it is sufficient to meet power requirements;
legal restrictions-local or state, on the development of the hydroelectric site, and the use of the water;
the availability of turbines and generators of the type or capacity required;
the cost of developing the site and operating the system; and
the rate a utility will pay for electricity you generate (if you connect to their system).

Principal question is: do I have a site suitable for hydroelectric power production? To answer that question, we have to examine four factors.
The distance of head or vertical fall that the water source develops.
The amount of water available for generation.
The length of pipe needed to go from the water source to the hydropower plant.
The distance from the hydropower plant to the electrical load, whether that be storage batteries, or in the case of AC generation, the appliances themselves.

Given these four factors, we can determine not only if hydroelectric power generation is feasible, but which diameter of pipe is needed, which type of the available hydroplants to use, and approximate output and costs.

The first step in assessing the feasibility of any hydroelectric system is to determine the amount of power that you can obtain from the stream at your site. The power available at any place is primarily a product of the flow and “head.” Flow is amount of water flowing through the turbine and is typically measured in cubic meters per second – m3/s or in cubic feet per second – cfs or gallons per minute – GPM are used.
Head is a measure of the pressure of falling water available at turbine expressed in meter water column. This pressure is a function of the vertical distance that water drops and the characteristics of the channel, or pipe, through which it flows. It must be distinguished between gross head, which is the difference of elevation between the water surface of the forebay and the tail race and net head, which is the actual pressure available at the turbine. To obtain net head, allowances must be made for losses in the penstock and draft tube. Gross head can be determined by a topographical survey using levels and tape measures. Head is expressed in meters (or in feet in the USA). High flow and/or head means more available power. The higher the head the better, because less water is necessary to produce a given amount of power, and smaller, more efficient, and less costly turbines and piping can be used.
Hydroelectric sites are broadly categorized as “low” or “high” head. Low head typically refers to a change in elevation of less than 3 meters. A vertical drop of less than 0,6 meters will probably make a hydroelectric system unfeasible. A high flow rate can compensate for low head, but a larger, and more costly turbine will be necessary. It may be difficult to find a turbine that will operate efficiently under very low heads and low flow.

CONFIGURATION OF SMALL HYDRO POWER PLANTS
Small hydro turbines can be configured to operate efficiently at sites with a wide range of head and flow rates. In case of micro hydro systems with batteries the greater predictability of hydro resources can help reduce the size of other system components like battery banks. Battery banks for PV systems are usually sized to provide five days of cloudy-day power, while small hydro systems usually need only one or two days of storage. It is responsible to assess a hydro resource during both wet and dry seasons. It is the responsibility of anyone who uses a hydro resource to evaluate the effects that water diversion may have on the ecology of the waterway and understand any applicable regulatory or legal restrictions. A rule of thumb used by some hydro builders is to divert 10 percent or less of the stream’s minimum flow. Note that use, access to, control, or diversion of water flows is highly regulated in many countries. So is any physical alteration of a stream channel or bank that may effect water quality or wildlife habitat, regardless of whether or not the stream is on private property.

Determining Head
When determining head (fall), you must consider both gross or “static” head, and net or “dynamic” head. Gross head is the vertical distance between the top of the penstock (the piping that conveys water, under pressure, to the turbine) and the point where the water discharges from the turbine. Net head is gross head minus the pressure or head losses due to friction and turbulence in the penstock. These head losses depend on the type, diameter, and length of the penstock piping, and the number of bends or elbows. You can use gross head to approximate power availability and determine general feasibility, but you must use net head to calculate the actual power available. There are several ways to determine gross head. The most accurate technique is to have a professional survey the site. If you know that you have an elevation drop of several dozens meters, a less expensive, but less accurate technique is to use an aircraft altimeter. In some countries it is possible to buy, borrow, or rent an altimeter from a small airport or flying club. You will have to account for the effects of barometric pressure and calibrate the altimeter as necessary. Another option is to use the “hose/tube” method described below.
Whatever method you use, you will need to determine the vertical distance between the point where water will enter the penstock and the point where water will discharge from the turbine. Always be safety-conscious when working near or in a stream, especially in narrow or steep stream channels and fast flowing water. Never work alone. Never wade into water in which you cannot see the bottom and without first testing the depth with a stick.
To perform the “hose/tube” method you will need an assistant, 6 to 9 meter length of small-diameter garden hose or other flexible tubing, a funnel, and a yardstick or measuring tape. Begin by stretching the hose or tubing down the stream channel from the point that you have decided is the most practical elevation for the penstock intake. Have your helper hold the upstream end of the hose, with the funnel in it, under the water as near the surface as possible. While he/she does this, lift the downstream end until water stops flowing from it. Measure the vertical distance between your end of the tube and the surface of the water. This is the gross head for the section of stream between you and your helper. Have your assistant move to where you are and place the funnel at the same point where you took your measurement. Then walk downstream, and repeat the procedure. Continue taking measurements until you reach the point where you plan to site the turbine. The sum of these measurements will give you a rough approximation of the gross head for your site. Note that, due to the force of the water into the upstream end the hose, water may continue to move through the hose after both ends of the hose are actually level. You may subtract few centimetres from each measurement to account for this. It is best to be conservative in these preliminary head measurements.

Determining Water Flow
Environmental and climatic factors, as well as human activities in the watershed, determine the amount and characteristics of stream flow on a day-to-day and seasonal basis. A storage reservoir can control flow, but unless a dam already exists, building one can greatly increase cost and legal complications. You may be able to obtain stream flow data from the local offices, from the local engineer, or local water supply or flood control authorities. If you cannot obtain existing flow data for your stream, you will need to do a site survey. Generally, unless you are considering a storage reservoir, you should use the lowest average flow of the year as the basis of the system design. Alternatively, you can use the average flow during the period of highest expected electricity demand. This may or may not coincide with lowest flows. There may be legal restrictions on the amount of water that you can divert from a stream at certain times of the year. In such a case, you will have to use this amount of available flow as the basis of design.

Measuring flow is a little more difficult. This should probably be done in more than one place too. This is because most streams pick up water as they go. Therefore choosing the best spot for your system requires careful consideration of several things. There are several ways to measure flow; here are two. In both cases, the brook water must all pass through either a pipe or a weir. A common method for measuring flow on very small streams is the “bucket” method. This involves damming the stream with logs or boards to divert the stream flow into a bucket or container. This method is the easiest way of measuring flow for streams with up to 5 litres per second or so, which accounts for most small hydro sites by far. You’ll need to construct a temporary dam of sorts at the water source. Than fit a short length of pipe large enough to handle all the water you plan to use for generation into the dam. Using a bucket of known capacity and a stopwatch you will have to estimate the time - how long it takes to fill the bucket. Repeat several times to determine that your technique is accurate. The rate that the container fills is the flow rate. For example, 20 litre bucket that fills in one minute is a flow rate of 20 litres per minute.

You can also try the following method to roughly estimate the flow in streams where it is impractical to attempt the bucket method. This method involves wading across the stream channel. Do not try this method if the stream is fast-flowing and over your calves! You could lose your footing, be swept downstream, and possibly drown. Never wade into any stream in which you cannot see the bottom! Always check the depth and character of the stream bed with your stick before you take a step. To perform this method, you will need an assistant, a tape measure, a yardstick or calibrated measuring rod, a weighted float (a plastic bottle half filled with water to give a better estimate of flow velocity), a stopwatch, and some graph paper. Begin by calculating the cross-sectional area of the stream bed during the time of lowest water flow. To do so, select a stretch of the stream with the straightest channel and most uniform depth and width as possible. At the narrowest point of this stretch, measure the width of the stream. Then, with the yardstick, walk across the stream and measure the water depth at 30 centimetres increments across the stream. Be sure to keep the measuring stick as vertical as possible. You may want to stretch a string or rope across the stream with the increments marked on it to assist in this process. Plot these depths on a piece of graph paper. This will give you a cross-sectional profile of the stream. Determine the area of each block or section of the stream by calculating the areas of the rectangles and triangles in each section. (Area of a rectangle = length x width; area of a triangle = ½ base x height). Add the areas of all the blocks together for the total area.

Next, determine the flow velocity. From the point where you measured the width, mark a point at least 10 meters upstream, and release the weighted float in the middle of the stream. Carefully record the time it takes the float to pass between the two points. Make sure that the float does not hit or drag on the bottom of the stream. If it does, use a smaller float. Divide the distance between the two points by the float time in seconds to get flow velocity in meters per second. Repeat this procedure several times to get an average value. The more times you do so, the more accurate your estimate will be. If the float gets hung up or “stalls,” start over, or this will throw the average off. Multiply the average velocity by the cross-sectional area of the stream. Multiply this value by a factor that accounts for the roughness of the stream channel (0.8 for a sandy stream bed, 0.7 for a bed with small to medium sized stones, and 0.6 for a bed with many large stones). The result will be the flow rate in cubic meters per second.

Keep in mind that this value will be the flow at the time of measurement. You should repeat the procedure several times during the low flow season to more accurately estimate the average low water flow. You do not have to measure the water depth each time. You can simply measure the water depth above, or below, the water level when you first measured the stream, and calculate the area of greater or less water, and add or subtract this from the baseline area. Alternatively, you may be able to install a gauge (made from a calibrated rod or post) on the bank so that you can easily read the water depth and calculate the cross-sectional area of the stream. You will need to repeat the flow velocity procedure each time, however.
You may be able to correlate your survey data with long term precipitation data for your area, or flow data from nearby rivers, to get an estimate of long-term, seasonal low, high, and average flows for your stream. Remember that, no matter what the volume of the flow is at any one time, you may be able to legally divert only a certain amount or percentage of the flow. Also try to determine if there any plans for development or changes in land use upstream from your site. Activities such as logging can greatly alter stream flows.

LOSSES IN PIPELINE SYSTEMS
In real fluid flows, losses occur due to the resistance of the pipe walls and the fittings to this flow and lead to an irreversible transformation of the energy of the flowing fluid into heat. Two forms of losses can be distinguished: losses due to friction and local losses.
Losses due to friction originate in the shear stresses between adjacent layers of water gliding along each other at different speed. The very thin layer of water adhering the pipe wall does obviously not move while the velocity of every concentric layer increases to reach maximum velocity at the centre-line of the pipe. If the fluid particles move along smooth layers, the flow is called laminar or viscous and shear stresses between the layers dominate. In engineering practice however, the flow in a pipeline is usually turbulent, i.e. the particles move in irregular paths and changing velocities. It is important to use pipelines of sufficient diameter to minimise friction losses from the moving water. When possible the pipeline should be buried. This stabilises  the pipe.
Local losses occur at changes of cross sections, at valves and at bends. These losses are sometimes referred to as minor losses since in long pipelines their effect may be small in relation to the friction loss.

Determining Power
At most sites, what is called run of river is the best mode of operation. This means that power is produced at a constant rate according to the amount of water available. Usually the power is generated as electricity and can be eventually stored in batteries. The power can take other forms: shaft power for a saw, pump, grinder, etc. Both head and flow are necessary to produce power. Even a few litres per second can be useful if there is sufficient head. Since power = Head x Flow, the more you have of either, the more power is available.
To calculate available power, head losses due to friction of flow in conduits and the conversion efficiency of machines employed must also be considered. The simple formula for potential power output is following: