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Unformatted text preview: Watersheds, estuaries and human perturbations
Human Impacts on Estuarine Processes November 11, 2008 What Is a Watershed?
A watershed is the area of land that drains to a particular point along a stream particular point along stream Center for Watershed Protection EVERYONE EVERYONE Lives in a Watershed Center for Watershed Protection What are the What are the Impacts of Urbanization? Many Many Forms of Impervious Cover in the Urban Landscape
Sidewalks Roads Driveways Parking Buildings
Center for Watershed Protection How How Impervious Cover Impacts Water Quality Water Quality
Impervious Cover Influences: Cover Influences: • • • • • • Dry & Wet Weather Flow Channel Shape and Size Volume of runoff to receiving waters Speed of runoff to receiving waters of runoff to receiving waters Water quality Plant and Animal Habitat Water Water Quality Is Related to Impervious Cover
In a forest, rain soaks into the ground and is either taken up by tree roots or continues to move down through the soil and into the groundwater. • When rain falls on impervious cover, it cannot soak into the ground and instead becomes stormwater runoff.
3 2.5 2 Inches 1.5 1 0.5 0
Rainfall Parking Lot Runoff Forest Runoff • • Impervious cover produces 16 times more stormwater runoff than forest more stormwater runoff than forest. Impervious Impervious Cover Influences Wet Weather Flow Wet Weather Flow
When it rains, a large amount of water . . . it rains, large amount of water Runs off of Runs off of impervious impervious surfaces Enters the Enters the stormdrain stormdrain system Is directed straight to Is directed straight to rivers, rivers, estuaries and oceans Impervious Impervious Cover Influences Dry Weather Flow Dry Weather Flow
Especially for streams for streams Many streams draw from groundwater Impervious surfaces can Impervious surfaces can block block water from contributing to groundwater supply Results in lower stream flows during dry weather Impervious Impervious Cover Influences Wet Weather Stream Flow Weather Stream Flow
The large amount of stormwater runoff in the stream stream system can cause: More Frequent Flooding Higher Flood Levels Impervious Impervious Cover Influences Stream Shape and Size Stream Shape and Size
Large amounts of stormwater runoff due to Large amounts of stormwater runoff due to impervious impervious cover can: • Erode stream banks, making the Erode stream banks making the
banks banks steeper and the channel wider • Deposit soil on the stream bottom, making the stream more shallow • Cause straightening of the channel Relationship Relationship Between Impervious Cover and Stream Quality Cover and Stream Quality
Good Impervious Cover Model Stream Quality
Severely Damaged 10% 25% 40% 60% 100% Watershed Impervious Cover Impervious Impervious Cover Influences Water Quality
Pollutants build up on impervious surfaces and wash off into the stream system when it rains wash off into the stream system when it rains. Harmful Harmful Pollutants in Runoff
Bacteria Nutrients Pesticides Oil & Grease Muddy Water Heavy Metals (e.g. Zinc, Copper, Lead) Impervious Impervious Cover Influences Habitat Quality Habitat Quality
Impervious cover changes the natural stream stream environment, resulting in: Smothering of Habitat by Sediment Deposits Loss of Habitat Variety Loss of Stream Buffer Geomorphological Effects of Geomorphological Effects of Urbanization on Streams
• • • • • • • • Stream widening & erosion Reduced fish passage Degradation of habitat structure Decreased channel stability channel stability Loss of pool-riffle structure Fragmentation of riparian tree canopy of riparian tree canopy Embeddedness Decreased substrate quality <5% impervious surface impervious surface Good riparian canopy Little erosion Photo Copyright 1999, Center for Watershed Protection 8-10% impervious surface Erosion of stream bed apparent Loss of wetted perimeter of wetted perimeter Photo Copyright 1999, Center for Watershed Protection 10% impervious cover Visibly impacted Exposed tree roots tree roots Double its size Eroded stream bed Photo Copyright 1999, Center for Watershed Protection 20% impervious cover Erosion Decreased substrate quality due to flushing flushing Photo Copyright 1999, Center for Watershed Protection Woody debris allows retention of carbon, sediments, and nutrients and provides habitat for insects This study conducted by Chris May et. al. defines the inverse relationship between large woody debris and watershed urbanization. Piping and culverts cut off fish spawning and migration patterns Photo Copyright 1999, Center for Watershed Protection 20% impervious cover Absence of vegetation to hold together bank structure Photo Copyright 1999, Center for Watershed Protection 30% impervious cover Increased stream size by factor of 5-10 Major erosion Photo Copyright 1999, Center for Watershed Protection Increased stormwater flow causes downcut in stream Forest and floodplain are now disconnected Photo Copyright 1999, Center for Watershed Protection Near complete loss of habitat value Photo Copyright 1999, Center for Watershed Protection Another example of little real habitat value habitat value Photo Copyright 1999, Center for Watershed Protection What What It Means for Streams
Sensitive Streams St Impacted Streams St < 10% Impervious Cover 10-25% Impervious Cover Diagnosis: • Healthy stream • Good water quality • Supports diverse aquatic life • Potential to be excellent • Very vulnerable to development Prescription: Requires greatest level of protection, including land conservation Diagnosis: • Classic suburban stream • Water quality depends on watershed protection techniques • Can support fairly diverse aquatic life • Streambank erosion noticeable Prescription: Requires extensive protection, including stormwater management. What What It Means for Streams
Damaged Streams Severely Damaged Streams 25-60% Impervious Cover >60 % Impervious Cover Diagnosis: • Channel highly eroded • Poor water quality • Supports very few species, no sensitive species • Use of stream limited by health concerns Prescription: Careful restoration and stewardship can improve water and habitat quality Diagnosis: • Channels are highly modified and have few natural features • Poor water quality and limited Poor water quality and limited aquatic aquatic life • Does not support many human uses like fishing uses, like fishing Prescription: Pollution prevention can help reduce pollutants delivered downstream Santa Monica Bay, California
• Ballona Creek Watershed • Los Angeles, CA • Highly urbanized • Large population ~18 population million • 2nd largest city in the US • High % of impervious surfaces • Large topographic features • Subject to episodic to episodic large rain events Los Angeles Ballona Creek Drainage Basin Ballona Creek
• Army Corps project • Handles large drainage basin 130 sq. miles • Numerous point sources and non point sources inputs • Altered creek bed allows minimal sedimentation SCCWRP Study
• Found maximum degradation of habitat • Upstream conditions for microbial contaminants were worse than downstream • More than half of the samples taken from the water in the Creek had human viral pathogens, some in surprisingly high concentrations • Were capable of utilizing the flow information, the microbiological information, and environmental parameters to model loading of contaminants to the Pacific Ocean • Demonstrated that the whole Creek needs to be managed, not just the end of the system Hydrological Effects of Hydrological Effects of Urbanization
• • • • • • • Disruption of natural water balance Increased flood peaks flood peaks Increased stormwater runoff More frequent flooding fl Increased bankfull flows Lower dry weather flow Stormwater (fresh) lens over seawater (fresh) lens over seawater This diagram shows how development and its corresponding increase in impervious cover di disrupts the natural water balance. In the post-development setting, the amount of water running off the site is dramatically increased. Consequences of Habitat Decline
• • • • • • Decline in aquatic insect diversity Decline in fish habitat quality Decline in fish diversity Loss of sensitive coldwater & salmonoids Reduced spawning of anadromous & resident fish Decline in wetland plant & animal community in wetland plant animal community diversity ...
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This note was uploaded on 01/03/2009 for the course ENST 471 taught by Professor Noble,rachael during the Spring '08 term at UNC.
- Spring '08