Natural Springs[edit | edit source]
Humans and Springs[edit | edit source]
Naturally occurring springs are responsible for determining the settlement sites of many ancient communities throughout the world. Many people respect springs, and many find them to be sacred and hold special qualities. Throughout human history the freshness of their waters has quenched many thirsty souls, and their reliability has sustained many communities. Springs occur naturally throughout the world where the subsurface water table is exposed at the surface. There are several ways springs can be classified. The type of aquifer they come from, the geological features that form them, the distribution of their discharge, their temperature and chemical constituents are all distinguishable traits with which to classify them. They come to the surface either by gravity or under pressure, and range in amount of flows from just a trickle to up to 250 million gallons/day (Kincaid, 2009). Springs can typically be found in places with high relief and ample precipitation. The groundwater that surfaces is naturally filtered through subsurface media. The quality of spring water is dictated on what constituents are in the subsurface but is generally adequate for potable water. Springs can surface in an exposed area or directly into a water body, such as a river or lake. An open exposure typically pools and flows in a channelized fashion offering an easily catchable source of water. Given their high water quality and widespread distribution, natural water springs have provided clean drinking water to humans for generations around the globe.
Spring Development[edit | edit source]
When developing this clean, reliable resource that nature has provided it is paramount to ensure that construction not only gets the desired flow but protects the spring for a sustainable future. It is of utmost importance in the use of a spring to ensure its water quality as well as its quantity. Overuse, proximal surface contamination, and improper development are the usual suspects for deteriorating spring quality. Use of the land near a spring by livestock, industry, transportation or agriculture can contribute contaminants to the water source, especially if they are up slope of the source. During runoff events, these contaminants can be carried to and mixed in with the spring water. Given the natural pressure that spring outlets are under, tampering with them can cause irreversible damage. During construction, the flow can be diminished by creating a back pressure which can permanently divert water from the spring to somewhere else with less resisting pressure. Compaction above and around the spring outlet area can cause changes to the subsurface flow path. For both physical and societal reasons, proper spring water catchment techniques should be of utmost importance in order to secure the value of the spring.
Spring Geology[edit | edit source]
The source of spring water comes from precipitation. As climates change, springs act as perfect indicators of a watershed’s reaction to change in precipitation. When rain or snow contacts the ground, some water particles evaporate or get used by plants, some runoff into rivers and the rest infiltrates into the ground. This groundwater moves by gravity and subsurface pressures towards rivers, lake and oceans, yet sometimes comes to the surface as a spring. A spring represents the groundwater at the surface. This occurs when the groundwater gradient slope is less than the surface slope, typically called a depression spring (Bryan 1919). A common spring type called a contact spring (Bryan 1919), has an impervious layer or conduit that guides the groundwater flow to the surface. This commonly occurs at geologic layer contacts that are vertically exposed with the less permeable layer on bottom acting as a shelf (Bryan 1919). Also faults and fractures in the substrata can create discontinuities and avenues within which water can flow to the surface. An artesian spring is one under higher pressures above causing water to breach the surface. These springs are commonly found where sinkholes are present (Stringfield 1966) and in karst topography. Springs are rarely found in horribly flat locales due to the flow potential from gravitational energy and head pressure. Water coming out of a spring may be centralized from some sort of conduit allowing for easier catchment, or it may be dispersed across a large area. Dispersion may be from various joints and fractures, vegetation or surface topography. Spring water may also form a collection pool near the spring eye which may make it difficult to locate. The physical geology of a spring must be considered to ensure effective development (Meuli 2001).
Effective Spring Catchment[edit | edit source]
The Right Spring[edit | edit source]
Above all, springs are delicate and finite water resources that demand careful management. Not every spring is suitable for human development. There are several factors that one must consider before altering anything within a spring catchment area. Before tapping a spring resource for human consumption, the water must have the quality suitable for human use, as well as have an ample supply.
Suitable Source (Water Quality)[edit | edit source]
The quality of the spring water is contingent upon the natural mineral compositions and concentrations within the aquifer, the contamination present, and the existence of bacteria. There are several tell-tale signs that spring water is adequate for human consumption. An obvious sign that it is not of potable quality is if no noticeable life surrounds the spring. This could denote extreme basic or acidic conditions that might be too energy intensive to treat. Observe the watershed above the spring location for use and/or any disturbance. Farming and industrial uses upslope a spring may have detrimental effects on spring water quality. Open air defecation and proximal sanitation units can cause direct viral, pathogenic and bacteriological contamination. Testing the water right at the source is essential before development. The most common tests to secure potable water include: total dissolved solids, pH, volatile organic compounds and E. coli forms. Table 1 shows various effective sensory tests that can be employed without the use of instruments. The safe water drinking guidelines from the World Health Organization provide acceptable levels of water constituents [1]
Adequate Supply (Water Quantity)[edit | edit source]
How much water is needed by the user depends on several technical and societal factors. Ultimately, the amount of water desired should be dependent upon the average daily demand of the user population. This is a product of the consumption per person and the total expected population for the duration of the development.
AVERAGE DAILY DEMAND = DESIGN FUTURE POPULATION * PER PERSON CONSUMPTION ADD (L/min) = Pf * Cpp (L/min)
A typical source for the consumption per person is 25 – 50 gal/person/day (WHO), and population must account for growth and design lifespan.
FUTURE DESIGN POPULATION = CURRENT POPULATION * (1+GROWTH RATE*DESIGN PERIOD/100) Pf = Pc * (1 + r % * td/100)
A handy spreadsheet model for calculating water systems made by the EWB-Fort Lewis College chapter. Though the amount of water needed for use is dictated by the user, the amount available is dictated by the spring discharge rate. Precise measurements of how much water the spring yields are paramount in any development scenario. Several measurement techniques can be used, but it is critical consider temporal variability when water quantity testing. The climate and precipitation fluctuate throughout the year affecting the water table levels and thus the spring flow rate. Calculations on spring yield should include the lowest seasonal flow. Minimal flows can be at the end of the dry season but are commonly found several months afterward and well into the wet season. The most accurate measurements account for every water particle in the spring system. Accounting for the total discharge from a spring can prove challenging (EWB, 2010). There are two distinct methods used to measure water flow. The most common way is to measure the amount of time needed to fill a certain volume. In this method, estimating the rate and subsequent receptacle choice aids the accuracy and efficiency of the process. Higher flows need larger measuring receptacles than lower flows. Ultimately the longer it takes to fill the receptacle the more accurate the data will be.
VOLUME (liters) / TIME (seconds) = FLOW RATE (L/s) V/t = Q
Another method to measure flow rate is by gauging channelized flow velocity over the cross sectional area of flow. VELOCITY = CHANGE IN DISTANCE / TIME v = (dx/dt) / t
If the cross-sectional area of the channel is found, and the average velocity of the spring discharge is measured the flow can be approximated.
FLOW RATE (m3/s) = VELOCITY (m/s) * AREA (m2) Q = v * A
The average velocity can be measured by sending floating particles down the channelized flow over a known distance while gauging the change in time. The cross sectional area can be measured in the ground but due to undulations in the natural topography the temporary construction of a weir proves helpful.
Not the Right Spring[edit | edit source]
If the spring investigation estimates show that the particular spring is not an adequate source of water for the user, several considerations may be made. The water quality is usually dynamic in nature and has the ability to improve. Detecting contamination and its source and removing it is an obvious solution. Assessing the land use upslope/upstream of the spring source and removing potential sources of contamination is the most effective tactic. Providing resource protection techniques such as fencing off the proximal collection area and constructing runoff diversion features may solve the water quality issue. Water treatment is another viable option.
In the event of a lack of desired quantity of spring discharge, reconsidering the water use should be an option. Spring water is considered higher quality than that of surface runoff in rivers and could be reserved for drinking water only while the other sources may be used for bathing and cooking (if properly treated). Consider tapping multiple springs if they exist in the catchment area that have the feasibility of being added to the supply system. This is encouraged in any spring water catchment development given the tentative reliability of spring flow and inaccurate pre-implementation spring assessments (Meuli, 2001).
Gravity Flow Collection Considerations[edit | edit source]
A common issue in pipe distribution related to the spring catchment technology is a lack of pressure head. Spring areas can form in topographic depressions and in relatively flat zones. When installing a distribution system to the spring intake system, a considerable effort during collection construction must be made in order to obtain adequate head pressure to ensure desired intake flows. This is done by surveying the area and ensuring that the flow energy is adequate using the hydraulic grade line (HGL) and pipe elevations as an evaluation. The hydraulic grade line is simply the sum of the pressure head over the specific weight for a liquid and the elevation head.
HGL = z + p/y in meters
The sum of the hydraulic grade line and the velocity head is the energy grade line (EGL).
HGL + v2/2g = EGL
The piped distribution line elevations should not exceed the energy grade line elevation. If there is no flow entering the intake unit and is backing up at the point off spring discharge, quickly allow the spring water to flow freely to reduce back pressure. It is possible the flow line is above the hydraulic grade line and more elevation head is necessary. In this scenario, further pipeline trench excavation is advised.
Spring Catchment Design and Construction[edit | edit source]
Given the wide variation in springs, each pose developmental technicalities specific to their characteristics. General guidelines can be applied but must be adapted to fit each instance. Two design types are described in this document that were chosen based on point source only outlets, site-modification, and user finances. The spring box design works best where the spring daylights in one distinct location (1-2m in breadth). The pooled design takes into account single point source or a seepage area that concentrates into a pool that is proximal to point of origination. A major consideration in a spring catchment design is to minimize surface exposure of the water. This decreases the probability of contaminants entering the system contributed from runoff, contact with animals, humans and any another other source of potential contaminate (Niskanen, 2003). This is aided by ensuring that spring catchment construction is as close to the point of spring exposure as possible.
Spring Box[edit | edit source]
An effective spring catchment device collects all of the desired spring discharge into a unit and channels the water into a pipe for distribution. A spring box design takes into account that many natural spring environments make it difficult to capture all of the discharge and thus requires a fair amount of site manipulation to be effective. It is important to remember that the collection box is NOT a storage unit and that it only acts to collect the water from the spring discharge area. A storage unit must be located outside and below the spring catchment are to reduce compaction and disturbance (Meuli, 2001).
Precautions
Excavation of the spring outlet is necessary in order to adequately capture the entire discharge quantity, to ensure that construction doesn’t hinder the spring resource, and to provide the correct location of the collection box. If carefully excavated, the nature of the spring will become more visible and manageable (Meuli, 2001). In order to obtain the most reliable spring discharge, excavation and construction should be done during the dry season, although knowing ht extent of the spring discharge during peak flows should be noted and accounted for in construction. As stated before this method requires a fair amount of spring manipulation and thus increases the probability of irreversible spring resource damage by compaction and pressure reversals. Once a flow path to the spring is restricted and exit pressures are subsequently increased, the potential for the water pressure to be forced out at another location greatly increases. This alternate route may result in a less tortuous and resistive path for the flow and permanently change the spring outlet location. By building a makeshift collection unit and outlet pipe (i.e. a bucket and hose) spring water should be diverting during construction.
Construction
Once excavation is complete and the location of the spring outlet is clearly defined, construction of the spring box can begin. The foundation of the concrete structure should be on or just inside the impervious surface that is responsible for spring water flow. The schematic to the right shows a proposed spring box design constructed of concrete. Pipe intake and piped overflow have been excluded from design schematic due to specific design considerations but typically exist within the collection box. The intake pipe should be below the overflow pipe yet above the box floor by at least 3 inches to account for sedimentation (Hofkes, 1983). Both outlets should be at or below the elevation of the spring source to ensure back pressures do not accrue. The lateral ‘wings’ on the outside of the box act as barriers further entraining spring flow into the collection box. There must be a lid to the box to enable sedimentation clean out, water testing, and any maintenance that might occur.
Retention collection[edit | edit source]
The retention collection unit is designed for spring environments that naturally pool at the point of discharge. Although exposure to surface environments is more extensive and contamination mitigation is slightly compromised, these springs naturally collect the water and centralize it alleviating the need for excavation and forced collection techniques. This technique uses a minimum of construction costs.
Construction
This spring collection technique uses a pre-existing natural collection pool as its collection point that includes a piped intake design and a small check dam. The figure to the right shows the retention pool complete with a concrete reinforced check dam and piped intake structure. The piped intake consists of 6 looped rows of perforated pipe placed at varying heights to account for sediment build up, vegetation clogging and fluctuating spring flows. A screen is wrapped around the intake apparatus as a strainer to further reduce clogging of perforated pipe. The intake pipe outlet is level with the spring eye outlet. In most low flow springs, sedimentation rates are low, and shallow clean out offers easy maintenance. The advantages of this design are mainly its low cost and needed technical ability. This option is more attractive to communities and agencies with low financial means and allows for the protection of more springs.
Concerns[edit | edit source]
Back pressures built up during spring catchment development must be careful analyzed. In the pool method, ensuring that the dam height is just enough to account for minimal sedimentation and the head pressure needed to get water into the intake structure or outlet pipe. Excessive pressure resulting from increased head due the dam height can cause irreversibly alter the spring flow discharge and location.
Monitoring and Operation[edit | edit source]
If constructed with these considerations and designs, spring catchments need very little monitoring and maintenance (Meuli, 2001). The operation maintenance that is needed to ensure water quality and quantity are preserved, should be done typically on a monthly basis. It is important to continually inspect the protection area, that the fence and vegetation are functional and adequate, no unintended use is occurring, runoff diversion is adequate and soil erosion is at a minimal and no new spring or seepage points have been created.
Common Mistakes and Trouble Shooting[edit | edit source]
To ensure quality spring resource development, several common mistakes are highlighted. Development of a spring resource can be futile if done improperly.
- Lack of protection zone and maintenance
- Trees planted too close, compromise collection structure
- not enough vegetation in place to combat erosion
- lack of surface water drainage mitigation
- no strainer in place to block debris entering the piped system
- overflow pipe position too high creating back pressure
- outflow gradient too flat for water intake
- no overflow drainage set up
- no clean out valve on piped system, no ventilation outlet creating a vacuum
Proper pre-implementation assessment and installation, along with preventative maintenance can alleviate most of these potential issues.
Impacts and Dissemination[edit | edit source]
Developing a spring resource can have many impacts on the local watershed and its ecology. The foremost issue is the altered stream flow downstream of the spring. Whether sequestering minor or major amounts of water from the once free flowing stream, changes in erosion rate, biological proliferation and possibly entire riparian ecosystems may be lost. The once untapped spring water resource falls into the hands of the users and whatever their interference may be. It is common for springs to fall prey to abuse, misuse and destruction either by contamination or overuse. As with any human alteration to the environment, careful consideration must be made what the best uses and treatment is for the natural spring resource. Given the overwhelming need for fresh water, there are many springs that have been developed and are in the process of being developed using these and similar designs. Non-governmental organizations, government agencies and private communities are all common spring developers. Dissemination of this technology is unique in that there are many functioning spring catchment design depending on the various spring environments. These must be built on site and should be done under supervision of a technical expert.
References[edit | edit source]
Arno, K. et. al., “Slope deposits and water paths in a spring catchment”, Frankenwald, Bavaria, Germany.
Bryan, K. ‘Classification of springs’. In: Journal of geology, vol. 27, p. 522-561, 1919.
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EWB, Experience working with Engineers without Borders in Laos, 2010
Hanson, B.D. Water and Sanitation Technologies: A Trainers Manual. Peace Corps, March, 1985.
Hart, W., “Protective Structures For Springs: Spring Box Design, Construction and Maintenance”, Michigan Technological University, Houghton, MI, 2003.
Heinz, B., et. al. “Vulnerability of a karst spring to wastewater infiltration” (Gallusquelle, Southwest Germany). Austrian Journal of Earth Sciences, 99, 11-17, 2006.
Hofkes, E.H. (ed.), Small Community Water Supplies: Technology of Small Water Supply Systems in Developing Countries, IRC Technical Paper No. 18, Wiley & Sons, Chichester, 1983.
Jennings, G. D., “Protecting Water Supply Springs”, Water Quality and Water Management. 1996.
Kincaid, T. “Where’s the Water Come From? Toward a Water Budget for the Wakulla Spring” GeoHydros, Inc., 2009.
Kovács, A. and Perrochet, P. A quantitative approach to spring hydrograph decomposition. Journal of Hydrology, 352 (1-2), 16-29, 2008.
Meuli, C., Wehrle, K. Spring Catchment. Manuals on Drinking Water Supply and Sanitation; Vol 4, St. gallen, Switzerland, SKAT, 2001.
Ministry of Irrigation and Water Resources and UNICEF, Technical Guidelines for the Construction and Management of Protected Springs and Roof Water Harvesting, 2009
Niskanen, Matthew, "The Design, Construction, and Maintenance of a Gravity-Fed Water System in the Dominican Republic," Department of Civil & Environmental Engineering, Michigan Technological University, Houghton, MI, 2003.
Rehrl, C., Birk, S., “Hydrological Characterisation and Modelling of Spring Catchments in a Changing Environment”, Austrian Journal of Earth Sciences, Volume 103, pp 106-117, 2010.
RWSSP: Technical Advisory Note 4.91, Water Supply - Spring Catchment and Filtration, 2009.
Savary, I. “Investigation of springs: the most effective method for estimating water resources in carbonate aquifers”, Resources Journal (Proceedings of the International Symposium on Development of Groundwater Resources), vol. 1, p. 53-62, 1973.
Smith, G. “Rural Water System Sustainability: A Case Study of Community-Managed Water Systems in Saramaka Communities”, Michigan Technological University, 2011.
Stringfield, V. T. and H. H. Cooper, Jr. 1951. Geology and Hydrologic Features of an Artesian Submarine Spring East of Florida. Florida Geological Survey Report of Investigations No. 7(2). 16 pp.
Technical Training Manual No. 5, Construction Design Course. Local Development Department, Ministry of Home and Panchayat, UNICEF, 1978.
Valdiya, K. S., Bartarya, S.K., “Hydrogeological studies of Springs in the Catchment of the Gaula River, Kumaun Lesser Himalaya, India”. Mountain Research and Development. 1991.
Water Engineering and Development Center (WEDC). The Worth of Water: Technical Briefs on Health, Water and Sanitation. Intermediate Technologies, London, 1991.
Wang, H. F. and Anderson, M. P., Introduction to Groundwater Modeling. Academic Press, San Diego, CA, 237 pp. 1995.
Zimmerman, T. A manual on watershed resources management in the western highlands of Cameroon: basic information for technicians working on soil – forest and water conservation in water intake areas and watersheds of rural water supplies. Bamenda, Cameroon, Helvetas Cameroon, 1996.
