files/AU3PEEpTBSQKrzIjG1oQ forum otoole
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Sediment Removal vs.
by Daniel J. O’Toole
Studies that examine sediment starvation in streams and rivers neglect to consider the pur-
Sediment Starvation: Is One Environmental Remedy Making Another Environmental Problem Worse? poseful and mandated removal of sediment from stormwater runoff. Is the physical removal
Daniel J. O’Toole, P.E., CFM, LEED AP, is director of civil engineering at Quality Environmental Professionals Inc. (QEPI) in Indianapolis, IN. He has been working with stormwater management and environmental issues for more than 20 years. E-mail: [email protected].
of sediment from stormwater directly exacerbating sediment starvation in streams and rivers? Environmental policies force humans to change behaviors or processes in order to illicit a desired result. Too often the desired result is connected to
a complex system that also changes as a result of the policy. Environmental policies have a long
View along the banks of the Mississippi River.
18 em april 2014
Copyright 2014 Air & Waste Management Association
awma.org
tradition of addressing one problem while creating another (see sidebar at lower right). Unintended consequences may be caused by short-sightedness, knee-jerk reactions, or a lack of understanding of the environmental systems involved. Advocates may be so eager to realize the immediate effects of a policy that they give no consideration to other potential consequences. Studies that examine sediment starvation in streams and rivers neglect to consider the purposeful and mandated removal of sediment from stormwater runoff. Are these researchers ignoring a potential unintended consequence from an otherwise good policy?
Too Little Sediment: Hungry Water Stormwater runoff is generated when precipitation from rain and snowmelt flows over the ground surface. A certain percentage of the precipitation evaporates, another percentage seeps into the ground, and the remaining portion flows overland or via storm sewers into our lakes, streams, and rivers. Sediment and other materials are picked up and suspended into the runoff as the stormwater flows overland. Sediment plays an integral part in the ecosystem of rivers and streams. The amount of suspended sediment helps determine the types of wildlife and plant life that adapt to each environment. Some species prefer high suspended sediment content that provides camouflage from sight-feeding predators while others rely on clearer water.2 Sediment is transported mostly as a suspended load of clay, silt, and sand held aloft in the water column by turbulence. The rate of sediment transport typically increases as a power function of flow. As an example, a doubling of the flow produces more than a doubling in sediment transport.3 The construction of dams, levies, and bank stabilization projects has disrupted the natural movement of sediments in most waterways.2 All dams trap sediment to some degree and most alter the flood peaks and seasonal distribution of flows. This changes the character and functioning of the river.3 Upstream of a dam, most of the suspended
awma.org
sediment is deposited in the calm water of the reservoir. Downstream, water released from the dam possesses the energy to move sediment, but has little or no sediment content remaining. This clear water is often referred to as “hungry water,” because the excess energy is typically expended on eroding the channel bed and banks. Channel erosion below dams is frequently accompanied by a change in particle size of the bed. Gravels are moved and finer materials are suspended into the flow and transported downstream, leaving a coarse layer of gravel, cobbles, and boulders.3 The coarse bed can cause adverse effects to fish species that depend on spawning. The removal of the finer materials also deepens the watercourse. This can affect flooding patterns. The deeper sections become isolated from their floodplains. The ecosystem of the floodplain relies on the nutrient exchange provided from its inundation by occasional floodwaters. Rivers tend to cut into one bank and deposit sediment on the other bank as they flow. This natural meandering helps provide equilibrium between the flow energy and the amount of sediment carried, as well as creating an ecosystem dependent upon the
Unintended Consequences • In 2007, the U.S. government mandated replacement of incandescent bulbs in favor of mercury-ladened compact fluorescent bulbs. The intent was energy conservation, but the result is increased exposure to mercury for individuals and increased disposal of mercury into landfills. • In 2008, riots broke out in various locations around the world in response to rising corn prices. The World Bank studied the price jump and determined that it was an unintended consequence of biofuel production. They concluded that the biofuel producers’ demand for corn pushed prices higher for everyone, including those who needed corn for food.1 • In 2009, a water conservation program in Los Angeles (requiring residents to water lawns only on Mondays and Thursdays) resulted in multiple catastrophic water main breaks due to the extreme pressure drops on watering days. The desired result was water conservation. The unintended result was very costly.
Copyright 2014 Air & Waste Management Association
april 2014 em 19
which can prohibit the growth of algae and rooted aquatic plants. Increases in sedimentation can lead to a reduction of the depth of the channel and a disruption of the aquatic ecosystem by altering or destroying the existing habitat.
Dams along the Missouri, Mississippi, and Ohio rivers are contributing to enough sediment loss that the Mississippi Delta is slowly sinking.
creation of sandbars and depositional areas. Levies and bank stabilizations prevent the natural meandering of waterways, reducing the amount of sediment transported and negatively impacting the ecosystem the meandering supports. The Mississippi River watershed covers nearly half the United States and discharges into the Gulf of Mexico via the river’s multi-lobed delta. Since the 1930s, Louisiana has lost nearly 1,900 square miles of land. Land formed by river sediments naturally subsides and sinks over time. Dams along the Missouri, Mississippi, and Ohio rivers are contributing to enough sediment loss that the Mississippi Delta is slowly sinking. Sediment deposition and accretion by plant growth replaces this land over time in a balanced setting. Currently, the subsidence is outpacing the natural depositional replacement.4
Too Much Sediment: Stormwater and Suspended Solids As construction and development increases in a watershed, the area of permeable surface that allows stormwater infiltration decreases. The increase in hard impermeable surfaces results in an increase in stormwater runoff volumes, peak flow rates, and a degradation of the runoff quality. The runoff can contain increased quantities of sediment, oxygendemanding compounds, nutrients, metals, chlorides, and other constituents. These additions to the runoff are proven to cause detrimental effects on the receiving waters.5 High levels of turbidity limit the penetration of sunlight into the water column, 20 em april 2014
Volume and peak flow issues have been addressed by local stormwater ordinances for some time now. Addressing stormwater quality issues is a more recent development. On November 1, 1999, the U.S. Environmental Protection Agency (EPA) announced implementation of the Clean Water Act Stormwater Phase II Rule. Phase II specifically addressed stormwater runoff as a source of water pollution and introduced best management practices (BMPs) as a method of improving the quality of the runoff. BMPs are treatment techniques designed to improve the quality of stormwater runoff before discharging it to an outlet point. Sediment (primarily from construction sites) was identified as the single largest cause of impaired water quality in rivers and the third largest cause of impaired water quality in lakes. Individual states and local jurisdictions were tasked with implementing Phase II. BMPs requiring the removal of 80% of the total suspended solids (TSS, also known as sediment) from the stormwater runoff became a standard component of construction projects and postconstruction stormwater management plans. On December 5, 2013, EPA announced a collaborative framework for implementing the Clean Water Act Section 303 (d) Program with individual states. Section 303 (d) requires states to develop lists of impaired waters and develop a total maximum daily load (TMDL) for each pollutant. The TMDL is a calculation of the maximum amount of a pollutant that a water body can receive and still safely meet water quality standards. Sediment has been identified as a primary pollutant requiring a TMDL. BMPs addressing suspended solids will continue to be used to address water quality.
The Questions Studies examining the effects of sediment starvation in rivers and streams cite multiple causes to explain the problem. The causes most often cited include dams, levees, and reservoirs. Most studies focus on
Copyright 2014 Air & Waste Management Association
awma.org
Power Plant Pollutant Control “MEGA” Symposium August 19-22, 2014 t#BMUJNPSF .%
5IFJOUFSOBUJPOBMMZSFOPXOFE.&("4ZNQPTJVNSFUVSOTJOUPBEESFTTJTTVFTSFMBUFEUPQPXFSQMBOUFNJTTJPOTUISPVHIUIF DPNCJOFEFòPSUTPGGPVSLFZJOEVTUSZQMBZFSToUIF64%FQBSUNFOUPG&OFSHZ %0&
UIF&MFDUSJD1PXFS3FTFBSDI*OTUJUVUF &13*
UIF 64&OWJSPONFOUBM1SPUFDUJPO"HFODZ &1"
BOEUIF"JS8BTUF.BOBHFNFOU"TTPDJBUJPO "8." #ZTIPXDBTJOHUIFMBUFTUEFWFMPQNFOUTBOEPQFSBUJPOBMFYQFSJFODFXJUIQPMMVUJPODPOUSPMTGSPNGPTTJMöSFEQPXFSQMBOUTJOMJHIUPG UIFFWPMWJOHFOWJSPONFOUBMSFHVMBUPSZEJSFDUJPOT UIFUFOUI.&("4ZNQPTJVNXJMMVQEBUFTFBTPOFEQSPGFTTJPOBMTBOEQSPWJEFBO FYDFMMFOUMFBSOJOHFYQFSJFODFGPSFBSMZDBSFFSFOHJOFFST5IFGPDVTXJMMCFPOTUBUFPGUIFBSUNFUIPETGPSSFEVDJOH40Y /0Y $02, QBSUJDVMBUF NFSDVSZ BOEBDJEHBTFT BOEUFDIOJRVFTUPNBOBHFBTTPDJBUFEJNQBDUTPOMJRVJEFõVFOUT"UUFOEFFTDBOSFDFJWF 1SPGFTTJPOBM%FWFMPQNFOU)PVSDSFEJUT
7JTJUwww.megasymposium.orgGPSNPSFJOGPSNBUJPO
the reach immediately downstream of these manmade alterations. Studies examining the loss of the Mississippi Delta and associated wetlands cite multiple theories that include a reduction of sediment being transported to the delta to restore what is being lost. Stormwater BMPs that address sediment remove more than silt and clay from the runoff. TSS also contains plankton, algae, and fine organic debris, which can serve as carriers of toxins (from pesticides or industrial sources) that can cling to suspended particles. Post-construction stormwater BMPs have been mandated in nearly all urban and suburban areas in the United States since the late 1990s. Since then, thousands of BMPs have been installed
across the United States. Although the effectiveness of each varies, all of the BMPs are reducing the amount of sediment reaching their respective receiving waters. The question is not whether the stormwater BMPs are necessary and effective. They are both. The questions become are the cumulative effects of the thousands of functioning BMPs affecting the composition of the receiving waters? Can suspended solids be removed from that much stormwater without feeling the effects on a macro scale? Is this another example of environmental policy creating unintended consequences? Will this issue become a bullet point in someone else’s article in 20 years? Time will tell. em
References 1. Zehner, O. “Unintended Consequences”. In Green Technology; P. Robbins, D. Mulvaney, and J.G. Golson, Eds.; Sage: London, 2011; pp. 427-432. 2. Missouri River Planning: Recognizing and Incorporating Sediment Management; National Research Council; The National Academies Press: Washington, DC, 2011. 3. Kondolf, G.M. Hungry Water: Effects of Dams and Gravel Mining on River Channels; Environ. Manage. 1997, 21 (4), 533-551. 4. Land Area Change in Coastal Louisiana 1932-2010 [Video]; U.S. Geological Survey, National Wetlands Research Center, Lafayette, Louisiana, 2011. 5. Erickson, A.J.; Weiss, P.T.; Gulliver, J.S. Optimizing Stormwater Practices: A Handbook of Assessment and Maintenance; Springer Science+Business: New York, 2013.
awma.org
Copyright 2014 Air & Waste Management Association
april 2014 em 21
Sediment Removal vs.
by Daniel J. O’Toole
Studies that examine sediment starvation in streams and rivers neglect to consider the pur-
Sediment Starvation: Is One Environmental Remedy Making Another Environmental Problem Worse? poseful and mandated removal of sediment from stormwater runoff. Is the physical removal
Daniel J. O’Toole, P.E., CFM, LEED AP, is director of civil engineering at Quality Environmental Professionals Inc. (QEPI) in Indianapolis, IN. He has been working with stormwater management and environmental issues for more than 20 years. E-mail: [email protected].
of sediment from stormwater directly exacerbating sediment starvation in streams and rivers? Environmental policies force humans to change behaviors or processes in order to illicit a desired result. Too often the desired result is connected to
a complex system that also changes as a result of the policy. Environmental policies have a long
View along the banks of the Mississippi River.
18 em april 2014
Copyright 2014 Air & Waste Management Association
awma.org
tradition of addressing one problem while creating another (see sidebar at lower right). Unintended consequences may be caused by short-sightedness, knee-jerk reactions, or a lack of understanding of the environmental systems involved. Advocates may be so eager to realize the immediate effects of a policy that they give no consideration to other potential consequences. Studies that examine sediment starvation in streams and rivers neglect to consider the purposeful and mandated removal of sediment from stormwater runoff. Are these researchers ignoring a potential unintended consequence from an otherwise good policy?
Too Little Sediment: Hungry Water Stormwater runoff is generated when precipitation from rain and snowmelt flows over the ground surface. A certain percentage of the precipitation evaporates, another percentage seeps into the ground, and the remaining portion flows overland or via storm sewers into our lakes, streams, and rivers. Sediment and other materials are picked up and suspended into the runoff as the stormwater flows overland. Sediment plays an integral part in the ecosystem of rivers and streams. The amount of suspended sediment helps determine the types of wildlife and plant life that adapt to each environment. Some species prefer high suspended sediment content that provides camouflage from sight-feeding predators while others rely on clearer water.2 Sediment is transported mostly as a suspended load of clay, silt, and sand held aloft in the water column by turbulence. The rate of sediment transport typically increases as a power function of flow. As an example, a doubling of the flow produces more than a doubling in sediment transport.3 The construction of dams, levies, and bank stabilization projects has disrupted the natural movement of sediments in most waterways.2 All dams trap sediment to some degree and most alter the flood peaks and seasonal distribution of flows. This changes the character and functioning of the river.3 Upstream of a dam, most of the suspended
awma.org
sediment is deposited in the calm water of the reservoir. Downstream, water released from the dam possesses the energy to move sediment, but has little or no sediment content remaining. This clear water is often referred to as “hungry water,” because the excess energy is typically expended on eroding the channel bed and banks. Channel erosion below dams is frequently accompanied by a change in particle size of the bed. Gravels are moved and finer materials are suspended into the flow and transported downstream, leaving a coarse layer of gravel, cobbles, and boulders.3 The coarse bed can cause adverse effects to fish species that depend on spawning. The removal of the finer materials also deepens the watercourse. This can affect flooding patterns. The deeper sections become isolated from their floodplains. The ecosystem of the floodplain relies on the nutrient exchange provided from its inundation by occasional floodwaters. Rivers tend to cut into one bank and deposit sediment on the other bank as they flow. This natural meandering helps provide equilibrium between the flow energy and the amount of sediment carried, as well as creating an ecosystem dependent upon the
Unintended Consequences • In 2007, the U.S. government mandated replacement of incandescent bulbs in favor of mercury-ladened compact fluorescent bulbs. The intent was energy conservation, but the result is increased exposure to mercury for individuals and increased disposal of mercury into landfills. • In 2008, riots broke out in various locations around the world in response to rising corn prices. The World Bank studied the price jump and determined that it was an unintended consequence of biofuel production. They concluded that the biofuel producers’ demand for corn pushed prices higher for everyone, including those who needed corn for food.1 • In 2009, a water conservation program in Los Angeles (requiring residents to water lawns only on Mondays and Thursdays) resulted in multiple catastrophic water main breaks due to the extreme pressure drops on watering days. The desired result was water conservation. The unintended result was very costly.
Copyright 2014 Air & Waste Management Association
april 2014 em 19
which can prohibit the growth of algae and rooted aquatic plants. Increases in sedimentation can lead to a reduction of the depth of the channel and a disruption of the aquatic ecosystem by altering or destroying the existing habitat.
Dams along the Missouri, Mississippi, and Ohio rivers are contributing to enough sediment loss that the Mississippi Delta is slowly sinking.
creation of sandbars and depositional areas. Levies and bank stabilizations prevent the natural meandering of waterways, reducing the amount of sediment transported and negatively impacting the ecosystem the meandering supports. The Mississippi River watershed covers nearly half the United States and discharges into the Gulf of Mexico via the river’s multi-lobed delta. Since the 1930s, Louisiana has lost nearly 1,900 square miles of land. Land formed by river sediments naturally subsides and sinks over time. Dams along the Missouri, Mississippi, and Ohio rivers are contributing to enough sediment loss that the Mississippi Delta is slowly sinking. Sediment deposition and accretion by plant growth replaces this land over time in a balanced setting. Currently, the subsidence is outpacing the natural depositional replacement.4
Too Much Sediment: Stormwater and Suspended Solids As construction and development increases in a watershed, the area of permeable surface that allows stormwater infiltration decreases. The increase in hard impermeable surfaces results in an increase in stormwater runoff volumes, peak flow rates, and a degradation of the runoff quality. The runoff can contain increased quantities of sediment, oxygendemanding compounds, nutrients, metals, chlorides, and other constituents. These additions to the runoff are proven to cause detrimental effects on the receiving waters.5 High levels of turbidity limit the penetration of sunlight into the water column, 20 em april 2014
Volume and peak flow issues have been addressed by local stormwater ordinances for some time now. Addressing stormwater quality issues is a more recent development. On November 1, 1999, the U.S. Environmental Protection Agency (EPA) announced implementation of the Clean Water Act Stormwater Phase II Rule. Phase II specifically addressed stormwater runoff as a source of water pollution and introduced best management practices (BMPs) as a method of improving the quality of the runoff. BMPs are treatment techniques designed to improve the quality of stormwater runoff before discharging it to an outlet point. Sediment (primarily from construction sites) was identified as the single largest cause of impaired water quality in rivers and the third largest cause of impaired water quality in lakes. Individual states and local jurisdictions were tasked with implementing Phase II. BMPs requiring the removal of 80% of the total suspended solids (TSS, also known as sediment) from the stormwater runoff became a standard component of construction projects and postconstruction stormwater management plans. On December 5, 2013, EPA announced a collaborative framework for implementing the Clean Water Act Section 303 (d) Program with individual states. Section 303 (d) requires states to develop lists of impaired waters and develop a total maximum daily load (TMDL) for each pollutant. The TMDL is a calculation of the maximum amount of a pollutant that a water body can receive and still safely meet water quality standards. Sediment has been identified as a primary pollutant requiring a TMDL. BMPs addressing suspended solids will continue to be used to address water quality.
The Questions Studies examining the effects of sediment starvation in rivers and streams cite multiple causes to explain the problem. The causes most often cited include dams, levees, and reservoirs. Most studies focus on
Copyright 2014 Air & Waste Management Association
awma.org
Power Plant Pollutant Control “MEGA” Symposium August 19-22, 2014 t#BMUJNPSF .%
5IFJOUFSOBUJPOBMMZSFOPXOFE.&("4ZNQPTJVNSFUVSOTJOUPBEESFTTJTTVFTSFMBUFEUPQPXFSQMBOUFNJTTJPOTUISPVHIUIF DPNCJOFEFòPSUTPGGPVSLFZJOEVTUSZQMBZFSToUIF64%FQBSUNFOUPG&OFSHZ %0&
UIF&MFDUSJD1PXFS3FTFBSDI*OTUJUVUF &13*
UIF 64&OWJSPONFOUBM1SPUFDUJPO"HFODZ &1"
BOEUIF"JS8BTUF.BOBHFNFOU"TTPDJBUJPO "8." #ZTIPXDBTJOHUIFMBUFTUEFWFMPQNFOUTBOEPQFSBUJPOBMFYQFSJFODFXJUIQPMMVUJPODPOUSPMTGSPNGPTTJMöSFEQPXFSQMBOUTJOMJHIUPG UIFFWPMWJOHFOWJSPONFOUBMSFHVMBUPSZEJSFDUJPOT UIFUFOUI.&("4ZNQPTJVNXJMMVQEBUFTFBTPOFEQSPGFTTJPOBMTBOEQSPWJEFBO FYDFMMFOUMFBSOJOHFYQFSJFODFGPSFBSMZDBSFFSFOHJOFFST5IFGPDVTXJMMCFPOTUBUFPGUIFBSUNFUIPETGPSSFEVDJOH40Y /0Y $02, QBSUJDVMBUF NFSDVSZ BOEBDJEHBTFT BOEUFDIOJRVFTUPNBOBHFBTTPDJBUFEJNQBDUTPOMJRVJEFõVFOUT"UUFOEFFTDBOSFDFJWF 1SPGFTTJPOBM%FWFMPQNFOU)PVSDSFEJUT
7JTJUwww.megasymposium.orgGPSNPSFJOGPSNBUJPO
the reach immediately downstream of these manmade alterations. Studies examining the loss of the Mississippi Delta and associated wetlands cite multiple theories that include a reduction of sediment being transported to the delta to restore what is being lost. Stormwater BMPs that address sediment remove more than silt and clay from the runoff. TSS also contains plankton, algae, and fine organic debris, which can serve as carriers of toxins (from pesticides or industrial sources) that can cling to suspended particles. Post-construction stormwater BMPs have been mandated in nearly all urban and suburban areas in the United States since the late 1990s. Since then, thousands of BMPs have been installed
across the United States. Although the effectiveness of each varies, all of the BMPs are reducing the amount of sediment reaching their respective receiving waters. The question is not whether the stormwater BMPs are necessary and effective. They are both. The questions become are the cumulative effects of the thousands of functioning BMPs affecting the composition of the receiving waters? Can suspended solids be removed from that much stormwater without feeling the effects on a macro scale? Is this another example of environmental policy creating unintended consequences? Will this issue become a bullet point in someone else’s article in 20 years? Time will tell. em
References 1. Zehner, O. “Unintended Consequences”. In Green Technology; P. Robbins, D. Mulvaney, and J.G. Golson, Eds.; Sage: London, 2011; pp. 427-432. 2. Missouri River Planning: Recognizing and Incorporating Sediment Management; National Research Council; The National Academies Press: Washington, DC, 2011. 3. Kondolf, G.M. Hungry Water: Effects of Dams and Gravel Mining on River Channels; Environ. Manage. 1997, 21 (4), 533-551. 4. Land Area Change in Coastal Louisiana 1932-2010 [Video]; U.S. Geological Survey, National Wetlands Research Center, Lafayette, Louisiana, 2011. 5. Erickson, A.J.; Weiss, P.T.; Gulliver, J.S. Optimizing Stormwater Practices: A Handbook of Assessment and Maintenance; Springer Science+Business: New York, 2013.
awma.org
Copyright 2014 Air & Waste Management Association
april 2014 em 21
