Science-based Guidelines for Successful Roadside Ditch Management to Mitigate Floods, Droughts and Degraded Water Quality.

Transcription

1 Science-based Guidelines for Successful Roadside Ditch Management to Mitigate Floods, Droughts and Degraded Water Quality Talk Outline 1. Flooding drivers i - climate change ii - watershed management 2. Ditch research project 3. Ditch management recommendations Rebecca Schneider Dept. Natural Resources Cornell University Dirt and Gravel Roads Conference September 22, 2009 April 16, 2007, NY Chautauqua # FEMA Disaster Flood events per County from Niagara Erie Cattaraugus 0x 1x 2x 3x 4x 6x 7x Orleans Genesee Wyoming Allegany Monroe Livingston Ontario Steuben Wayne Yates Seneca Schuyler Cayug a Chemung Jefferson Oswego Onondaga Tompkins Tioga Cortland Avg flood damage costs: ~$50 million/yr Broome Lewis Oneida Madison Chenango Flood damage estimates in U.S., 2002 R. Pielke, M. Downton, Z. Barnard-Miller Boulder, CO. St. Lawrence Herkimer Otsego Delaware Franklin Hamilton Sullivan Fulton Montg. Schohari e NY City Greene Ulster Orange Rockland Albany Clinton Essex Warren Saratoga Columbia Dutchess Rensselaer Putnam Washington Westchester Nassau Schenectady Suffolk A broader perspective - Precipitation has been increasing in NY and the Northeast Northeastern U.S. Climate Future directions 2006 Union of Concerned Scientists us-newyork.html

2 Poor Watershed Management Watershed divide Balance between precipitation, runoff, infiltration, and evapo-transpiration Watershed: all of the area which captures rainfall and contributes to stream flow, i.e. the bowl. Cross-section of a watershed Watershed divide rain Groundwater contribution base flow High flow Stream numbering Overland runoff via stream channel networks Low flow Photo: Y. Arthus Bertrand Natural stream flow patterns Impervious Surfaces: Rooftops Parking lots Driveways Compacted Soils: Lawns, Crop fields

3 Impervious surfaces impact the natural patterns of flow: in frequency and magnitude of floods in summer droughts degraded water quality erosion loss of diversity of fish and aquatic animals stream height post-development pre-development Talk Outline 1. Flooding i - climate change ii - watershed management 2. Ditch research project 3. Ditch management recommendations time (hrs/days/weeks) Roadside Ditches the unrecognized factor in stormwater runoff management Managed by highway staff to prevent road flooding and traffic accidents rarely linked to watershed mgmt issues What role do they play in flooding, droughts, and pollution? On-going Research on ditch networks 1) Map: ditch lengths, mgmt types connections to streams GPS and GIS mapping of the ditch networks relative to natural stream channel systems in 6 watersheds. 2) Monitor: Total water flow Suspended sediment Dissolved chemicals Bedload sediment Without Ditches With Ditches Paine s Creek Watershed, Lansing, NY

4 Ditches intercept ~1/4 of the surface runoff in our watersheds and shunt it rapidly downstream where it is injected as high flow into the streams. Ditch drainage basins Stream Road ditches Ditch outflows Mean Peak conc. (kg/m^3) Mean Peak conc. by Percent of exposed substrate at the bottom 7 6 Ditch 4 Ditch 2 5 Ditch 7 Ditch 3 (incised) 4 Ditch 8 Ditch 6 Ditch 5 old 3 Ditch 1 y = e x R 2 = Ditch 5 new 2 Ditch 3 (scraped) % exposed substrate at the bottom VEGETATED BARE Ditches are a source of sediment and associated contaminants to downstream waters, especially when scraped. Summary of Chemicals Transported in Ditches Nutrients Trace Metals Dissolved Chemical Loads Element Total load (kg) Ortho-Phosphates 1.43 Total P NO 3- + NO Al Mn 1.48 Fe Ni 6.39 Cu 1.28 Pb 0.25 Cr 3.79 A diversity of chemicals dissolved in the water and adsorbed on the sediment particles are transported by ditches downstream. Cations Zn 2.90 Na + 11, Mg K Ca 2+ 3, De-icers Anions As Large quantities of gravel, rocks and other bedload move out of ditches and form deltas in the streams.

5 Current Research: Potential influence on stream erosion. Moose River, Adirondacks Ditch influence on erosion? Current research: Ditches as conduits of human pathogens to downstream drinking water reservoirs Idexx s Colilert/Quantitray Method Methods E. coli Quantification Positive for Total Coliforms Positive for E. coli EPA Std. Talk Outline 1. Flooding i - climate change ii - watershed management 2. Ditch research project 3. Ditch management recommendations

6 Goal: To provide some guidelines for better roadside ditch design and maintenance which accomplish the following: 1) Reduce work load and costs. Guideline #1: Create and maintain a shallow, gently sloping ditch. easier to maintain by mowing many landowners will do it themselves safer for traffic less likely to erode 2) Keep stakeholders happy. 3) Prevent erosion, protect water, and maintain a healthy environment. Don t overditch inches depth is plenty deep enough to carry away stormwater Avoid the V-shaped ditch - the bottom is easily incised and starts the erosion process. Guideline #2: Plan ahead to prevent erosive water flows. Consider drainage areas upslope that may contribute to erosive flows. Use check-dams to slow velocities. Guideline #3 Wherever possible, mow ditches regularly instead of scraping.

7 Use hydroseeding immediately after ditching Hydroseed early in the season to allow sufficient growing time, and not immediately before rain. Guideline #4: Minimize erosion of gravel and rocks that move as bedload into streams. If scraping is necessary, do it in patches with vegetated strips left downslope to capture sediments. Use permeable pavements or vegetation along road shoulders. Guideline #5 Disconnect ditches from streams. Use infiltration basins or detention ponds that allow for groundwater recharge. Use multiple, under-road culverts to spread out the flow. Guideline #6 Reduce transfer of runoff from land to ditches. Increase infiltration of rain water on land associated with houses, parking lots, and farms. Guideline #7 Communicate! Be part of the dialogue and provide leadership concerning stormwater management with landowners and town government.

8 Questions? B. Hecht Road drainage is a critical component of traffic safety as well as flood prevention and water quality improvement! Acknowledgments: Collaborators: T.Walter, D.Buckley, K. Falbo, J. Diaz-Robles, B.Buchanan Funding: USDA CSREES, Cornell (funding); Cayuga Lake Watershed Network, Town of Candor, Cortland, Enfield Highway Depts., City of Ithaca Planning Dept.