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Sampling from Test Pits, Trenches and Stockpiles

John Poullain, P.E.


Course Outline

This four-hour online course provides general guidelines and practices for planning, designing and building ponds for multipurpose uses. Ponds are built for various water needs including irrigation, livestock, recreation and fish production. It discusses the methods for estimating storm runoff, spillway requirements and pipes through earth fill dams. Storm runoff estimates are based on several factors including type of soil, types of ground cover and condition, rainfall distribution, and time of concentration similar to the rational equation method. Other storm water management and protection practices are briefly described. Methods and materials used to seal pond sites and dams, establish vegetation, and maintain the pond are also considered. Pond construction and operations must comply with federal, state and local regulations to protect public safety and water quality.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:


Intended Audience

This course is intended for civil engineers, contractors and planners.

Benefit to Attendees

The student will become familiar with methods and techniques used to plan, design and build ponds for multipurpose uses. Designing and sizing the pond storage volume and dam embankment, and spillway and hydraulic estimating are presented. Ponds often are used to manage stormwater drainage at construction sites and developed areas in order to reduce erosion and runoff of sediments onto land and downstream waters. Basic guidance in the selection of sealing ponds, establishing vegetation and operation and maintenance are discussed. 


Course Introduction

This course covers the practices commonly used to plan, design and build ponds for uses including irrigation, livestock, fish production and recreation. Ponds or sediment basins are often used to temporarily manage the movement of storm water and sediments at construction sites. As land development increased, protection from runoff erosion and sedimentation are necessary to prevent off-site migration of surface water, sediments and pollutants which contaminate soil, groundwater, and wells and nearby bodies of water. Sediment contains soil particles along with petroleum products, metals, chemicals, corrosive acids, pesticides, organics and other pollutants. Control practices are needed to prevent erosion and off site sedimentation. Based on volume, sediment from erosion may be a larger pollutant of waterways and lakes than is toxic waste or chemicals. Land disturbed by pond construction activities requires precautionary measures to reduce soil erosion and sedimentation. A site must be investigated for a wide range of conditions, including soil types, rock, rainfall, surface drainage and surface and subsurface ground conditions.

Erosion occurs naturally but land development and land use changes accelerate it... Increased urbanization, with increased roof areas and paving and the clearing of woodland and grassland without proper conservation management create erodible land areas, speed up runoff and remove areas available for rainfall infiltration. Vegetation removal from land area will further accelerate erosion and siltation. Using detention or sedimentation basins or ponds attempts to keep the stormwater runoff rate from exceeding the predevelopment rate.

Detention Basins and Ponds
Detention basins and ponds reduce stormwater runoff velocities, trap sediment in water pools and then discharge the water at a controlled rate of flow. Detention basins may be converted to ponds later when properly altered and sediment is removed. The differences between these practices however, are the detention times, drainage areas served and height of dam embankments. Most detention basins are designed to store the first ½ inch of runoff from a design storm and release the remainder at a rate equal to that rate of runoff existing before development of the site.

Other Erosion Protection Practices  
Management practices also include overland flow diversion and perimeter protection of a watershed with earth berms and ditches, terraces, temporary swales, vegetation and controlled development along fills. Structural methods include riprap, cellular mattresses, earth berms and sediment fences.

Diversion Ditches and Berms - Runoff erosion of slopes can be reduced by intercepting and diverting water away from the top of slope with diversion ditching, diversion berms or a combination of both. They can be used to protect newly graded slopes until vegetation is established and across slopes to reduce the length of slope exposed to erosion. The fill for berms is usually provided from the ditch excavation.  The ditches may be seeded and mulched or sodded or for long-term erosion protection, stabilized with riprap, asphalt concrete, concrete etc. or by any combination of these. The diverted runoff should be discharged into a stable area through pipes or ditches lined with riprap, Portland cement concrete etc. for erosion protection.

Grading and Bench Terraces - Slopes that are too steep can be reshaped by grading the slope. It is more feasible to terrace slopes to protect small reaches only. Terracing slows rainfall and runoff by breaking the gradient of long steep slopes in steps. Ditching on a bench terrace may not be necessary since the benches are constructed to typically slope inward toward the top of slope in order to divert runoff water along the bench rather than down the slope.  

Swales - Swales are used in a similar fashion, as ditches but do not block traffic as ditches due to their wider and shallower channel cross section. A wider and shallower cross section reduces the stormwater velocity and potential for erosion. A wider but shallower trapezoidal channel compared with a v-ditch of equal area for instance will be shown to have a lower velocity of flow. Grassed swales also promote infiltration and help to remove sediments. The construction and maintenance of swales and ditches are similar.

Temporary Slope Drains, Flumes and Down Pipes - Flumes and downpipes are temporary structures used to carry concentrated flows down the face of a slope without erosive damage. Flumes are open channels lines with an erosive resistant material such as concrete, grouted riprap etc. Downpipes are made of corrugated plastic or metal. They have standard entrance sections and like flumes discharge to outlets stabilized with riprap aprons or sediment traps. The advantage of both practices includes prevention of erosion on steep slopes and they are intended for temporary erosion control until a slope is stabilized with vegetation and/or practices.

Straw Bale Traps or Check Dams - Use of straw bales and sediment fences is limited to small drainage areas of about two acres and is intended to intercept and detain small amounts of sediments from a watershed. Straw bale traps however can be located across small swales. For large drainage areas and swales, which have concentrated flows, sediment basins are more suitable. Erosion will occur around or under the bales at adverse sites with steep slopes. Installation of straw bales is similar to the requirements of sediment fences. The bales should be entrenched at least four inches or backfilled with compacted soil and anchored with stakes. A stabilized bypass should be considered for sites with large stormwater flows to protect the integrity of the straw bale trap.

Vegetation - Site specific conditions must be considered to use vegetation. Success of vegetation depends on the climate characteristics, slope grades, site preparation and compatibility of vegetation with these conditions. Vegetation is one of the most commonly used methods for stabilization. It is relatively easy to maintain and establish since properly selected plants and grasses are self-maintaining. Erosion control matting may be necessary to hold the seed and soil in place until the vegetation is established. Slopes flatter than 1V on 2H or 3H is preferable especially for ease and safety in maintenance.

Vegetation protects a slope with the roots and exposed branches, stems. Surface flow velocity is reduced and the capacity for infiltration and water withdrawal from the soils is increased. Seedbed preparation, fertilizers, planting dates, rates of application and type of grasses will depend on the region, specific area for planting, time of year and as specified in the design plans. Also there are temporary and permanent plantings. Permanent seeding is typically for periods longer than 12 months with perennial grasses. Nurse crops are sometimes uses in the seeding mix. Annuals such as wheat or rye provide winter protection to enable the permanent grasses to become established and help in controlling weeds.

Soil Bioengineering - Woody vegetation is used for slope protection and slide repairs and usually provides greater slope protection than grasses alone. The woody vegetation can also be combined with a structural system, concrete block or 3-dimensional synthetic grids on steep slopes. The structure allows immediate slope protection and time for the vegetation to become established. Woody vegetation practices are well suited for areas with limited access for equipment and for short reaches with steep slopes.    

Riprap - There are several ways to place riprap. It can be mechanically placed along the slope or in wire baskets as a blanket over the slope. Riprap mattresses are relatively flexible and can adjust as changes from settlement or erosion occur. Minor damage can be easily repaired with additional stone to fill settlement or voids from erosion. A rule of thumb for mattress thickness is 1.5 times the thickness of the largest stone being used. Filter fabric or a drainage material is usually placed as an underlayment to protect from loss of fine soils and to allow for water seepage under the riprap.

Course Content

This course is based primarily on the United States Department of Agriculture Handbook 590, “Ponds – Planning, Design, and Construction”, (2004 Edition, 72 pages), PDF file. 

The link to the documents are as follows:

United States Department of Agriculture Handbook 590, “Ponds – Planning, Design, and Construction”

Glossary

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Course Summary

This course will serve as a guide for planning, designing and building multipurpose ponds. Siting the pond, necessary surveys, hydraulic design, and earth quantities for the dam, spillway, and appurtenances of a pond are discussed. It explains the techniques used to estimate stormwater runoff, construct stable dams and spillways, seal dams, establish vegetation and maintain ponds. The design, installation, type of materials, advantages and the effects of the physical site condition is also considered. 


Related Links

For additional technical information related to this subject, please visit the following websites or web pages:

http://www.errosioncontrol.com/ec.html
“Erosion control at Construction Sites”, information about erosion and sediment control and stormwater management from the journal “Erosion Control” published by the International Erosion Control Assc. 
                          
http://www.cwp.com/esc_practices.htm  
The Center for Watershed Protection provides technical tools to local governments and watershed organization watershed protection, restoration and research and stormwater management.

http://www.ems-i.com/wmshelp/Hydrologic_Models/Models/Rational/Rational_Method_Overview.htm
Software developed for modeling small watersheds and an overview of the rational methods, parameters and procedures to follow.


Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.