Statement of Impact and Objectives. Watershed Impacts. Watershed. Floodplain. Tumblin Creek Floodplain:

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1 Tumblin Creek Floodplain: Impacts Assessment and Conceptual Restoration Plan Casey A. Schmidt Statement of Impact and Objectives Urbanization has increased stormflow rate and volume and increased sediment, contaminant and nutrient loads to the Tumblin Creek floodplain. The goal of this project is to assess how impacts to the floodplain have affected the structure and functioning of the wetland. Floodplain The watershed is composed of 60% impervious surfaces. Urban/Built-Up Up is the dominant land use. Wetlands and forested uplands make up a portion of the land- use Watershed Watershed Impacts The basin is described as flashy, indicating a peaked hydrograph. Erosion and scour are common along the creek. Tumblin Creek is on the FDEP list of impaired water bodies. Bivens Arm is hypereutrophic Flow Rate Rainfall Event Hydrograph Post-development Pre-development Time Pre vs. Post development runoff characteristics from watershed Baseflow vs Stormflow Baseflow Stormflow 1

2 Major channelization occurred between 1949 and 1956 Extent of Channel in 1937 Channel and Spoil-Pile 2002 Floodplain Boundary 2

3 Impacts to the Floodplain Sedimentation: The end of the dredged channel has become the deposition zone for the suspended sediment from the watershed. Sedimentation Incised Channels: Channels have been incised through this sediment plume, thus confining flows to a smaller area. Trash: Massive amounts of trash have been deposited. Hydrologic Modification: Spoil-Pile Formation and Incised channels have altered the hydrology Soil subsidence: Soil subsidence has occurred in areas which are hydrologically isolated as a result of the spoil- pile formation. Channel Incising Trash Soil Subsidence 3

4 Project Objectives To assess the previously-mentioned impacts on the wetland floodplain. To understand how these impacts affect the functioning of the wetland with regards to water quality. Determine restoration plans to improve the functioning of the wetland and water-quality to Bivens Arm Lake. Assessment of Impacts I. Sediment Accretion Outline II. Suspended Sediment Characteristics III. Soil Characteristics IV. Phosphorus Isotherms. Summary Restoration Implications Sediment Accretion: Hypotheses Methods for Measuring Elevation Elevation: The zone immediately downstream of the channel has a higher elevation than surrounding areas. Timeline and Rate: The net sediment accretion rate of this downstream zone has increased since channel formation and land-use changes. Vegetation: The sediment accretion timeline and rate is indicated by a vegetative succession. Results: Cross-Sections Transect A Results: Elevation Interpolation A C B D E F G H I J Equivalent to 1 meter Equivalent to 20 meters Volume of the Spoil-Pile = 12,718 m 3 Footprint of the Spoil-Pile = 1.90 acres B C D E F G H I J Wetland boundary Soil Elevation Interpolated utilizing the spline function of the ArcGIS Spatial Analyst software. 4

5 Timeline of Sedimentation To determine when this sediment plume was created we utilized trees to determine how much sediment had accumulated above their roots. Where was this surveyed? Measuring Sedimentation Rate Acer rubrum (Red Maple) 27 years old Fraxinus profunda (Pumpkin Ash) 82 years old Nyssa sylvatica var. biflora (Swamp Tupelo) 127 years old Results: Root Flare Elevation by Species -20 Results: Sediment Accretion Root Flare Elevation (m.) Root Elevation (m) m m Tree Acer rubrum Fraxinus profunda Acer rubrum Fraxinus profunda Nyssa Sylvatica Nyssa sylvatica var. biflora Soil depth, cm ybp ybp Acer rubrum Fraxinus profunda Nyssa sylvatica var. biflora ybp m Distance Node (m) Distance from Transect Pin (m.) Soil surface averages 12 cm above Acer rubrum roots Tree age, years before present 5

6 Elevation (m) Present Day and Reconstructed Historical Soil Elevation Acer rubrum Fraxinus profunda Nyssa sylvatica var. biflora Sediment Accretion Conclusions Elevation: Elevation surveys indicate a rounded plume of high elevation immediately below the channel. Volume of the spoil-pile pile is 12,718 m 3 Footprint of the spoil-pile pile is 1.9 acres Timeline and Rate: Sedimentation rate has increased in the time period of watershed development and channel formation. Maximum integrated rate is 1.5 cm/yr 1 meter of sediment has accumulated in this area over the last 100 years Vegetation: Elevation increases have facilitated a change in species composition from obligate to facultative trees Distance from Node (m) Approximately 110x : Y scale Assessment of Impacts I. Sediment Accretion Outline II. Suspended Sediment Characteristics III. Soil Characteristics IV. Phosphorus Isotherms. Summary Restoration Implications Introduction to Sediment Fractionation Bivens Arm and Tumbling Creek have the highest sediment contaminant concentrations of the locations sampled in the Gainesville area (Durell et al. 2002). Lead and Chromium were listed as having metal concentrations of the greatest concern (Durell( et al. 2002). The goal of this section of research is to determine what role the floodplain may play in particulate contaminant removal prior to discharge to Bivens Arm. This study will also help the city to size a sedimentation basin upstream of the floodplain. Sediment Fractionation Hypotheses A majority of the mass of suspended sediment will settle rapidly. The concentration of Phosphorus and Metals which settle in longer time periods will be higher than those which settle in a short time period. Sediment Fractionation Methods Water was sampled in a section of the creek lined with concrete upstream of the floodplain. Three separate storms were sampled on 11/4, 11/5 and 11/19 of 2003 I then fractionating the suspended solids of a storm sample by settling time and analyzed it for Total P and Lead and Chromium. 6

7 Results: Total Sediment Mass Results: Phosphorus Mass by Settling Time Total Sediment Mass mg by Settling Time One Minute 2 24 >24 One Minute 2 24 >24 1 Minute 2 24 >24 P Mass Fraction by Settling Time Average sediment Concentration (mg/l) Standard deviation Average (mg of P/m 3 ) Standard deviation One Minute > Results: Phosphorus Concentration by Settling Time Results: Cr and Pb Mass Fractionation by Settling Time Chromium Mass by Settling Time One Minute 2 24 >24 Lead Mass by Settling Time min 2 hour 24 hour >24 hour Average (mg of P/m 3 ) Chromium One Minute > Average (mg of P/m 3 ) One Minute Lead > Y-Axis bars represent +/- Standard deviation Standard deviation Standard deviation Results: Cr Concentration by Settling Time Results: Pb Concentration by Settling Time min 2 hour 24 hour >24 hour min 2 hour 24 hour >24 hour Y-Axis bars represent +/- Standard deviation Y-Axis bars represent +/- Standard deviation 7

8 Suspended Sediment Fractionation Conclusions The total mass of suspended sediment was highest in the larger particle size. Particles which settle in the one minute time period, have a lower concentration of Phosphorus, Lead and Chromium than do smaller particles. Approximately 47% of phosphorus, 44% of lead, 19% of chromium could be effectively settled in conventional rapid sedimentation basins, residual fraction will require longer detention times than may occur in the floodplain Assessment of Impacts I. Sediment Accretion Outline II. Suspended Sediment Characteristics III. Soil Characteristics IV. Phosphorus Isotherms. Summary Restoration Implications Soil Characteristics Hypotheses The region immediately downstream of the channel will be indicated by higher bulk density and lower organic matter content. The regions on the opposite side of the spoil-pile pile from the creek will have lower bulk density and higher organic matter content. Soil Metal and Phosphorus concentrations will be highest in regions with longer detention time, not as affected by a high sediment load. Soil Sampling Methods Sampled along transects every 25 meters. Sampled the top 10 centimeters. We composited three samples Soil Bulk Density Organic Matter Content 8

9 Soil Phosphorus Soil Chromium Soil Lead Soil Characterization Conclusions The region downstream of the channel was characterized as having higher bulk density and lower organic matter content. The removal of particles containing the highest mass per unit area of Phosphorus, Lead and Chromium required a longer detention time. The detention time has been impacted by high amounts of sediment accumulation. Assessment of Impacts I. Sediment Accretion Outline II. Suspended Sediment Characteristics III. Soil Characteristics IV. Phosphorus Isotherms. Summary Restoration Implications Phosphorus Isotherms Hypotheses Phosphorus Isotherms will indicate a higher cumulative P sorption in areas of the floodplain with a longer detention time. The area of highest sediment accretion will have the lowest P sorption potential. Objective A calculation of the Equilibrium Phosphorus Concentration will indicate whether the soils are a source or sink during baseflow and stormflow. 9

10 Methods Results: Phosphorus Isotherms Soil Samples from the two distinct regions were composited. The soils were spiked with P concentrations of 0,0.1,0.25, 0.5, and 1 mg/l to calculate the Equilibrium Phosphorus Concentration. A Single-Point Isotherm of 100 mg/l was used to calculate total P sorption. West Downstream P retained (mg/cm 3 ) Sorption Equilibrium P Concentration by Zone Stormflow P Conc. = mg/l Desorption Baseflow P Conc. = mg/l Downstream West Water Column P Concentration (mg/l) Results: Maximum P Sorption Phosphorus Isotherm Conclusions P retained (mg P/cm 3 ) Maximum P Sorption by Region West Downstream The area most impacted by sedimentation of larger particles has a lower total P sorption than the less impacted region. Deposition of the large mass of heavy sediment has caused the soils downstream of the channel to be a source of soluble Phosphorus during baseflow and stormflow. The soils west of the spoil-pile pile are a sink for soluble P during stormflow and a small source during baseflow Equilibrium P concentration in Solution (mg P/L) Summary Sediment accretion rate has increased in the floodplain due to channelization and land-use changes. Sediment induced change in elevation has been significant enough to alter the vegetative composition. The channel and sediment plume have decreased the floodplains ability to act as a sediment sink, particularly for finer particles with higher concentrations of pollutants. Increased sediment accumulation has decreased the ability of the floodplain to remove soluble forms of Phosphorus which degrades water quality to Bivens Arm Lake. Restoration Implications: Detention Basins Detention Basin: Upstream removal of sediment through a detention basin is required in order for the floodplain to continue functioning to improve water quality as well as to maintain the vegetation and soils characteristic to a wetland. 10

11 Restoration Implications: Spoil-Pile Removal Acknowledgements Spoil-Pile Removal: Would increase the wetlands ability to remove particulate matter. Would allow flows to bypass the sediment mound thus facilitating soluble P removal. The City of Gainesville Public Works Department for providing funding. Alice Rankeillor project manager Dr. Mark Clark, Dr. Joe Prenger,, Dr. Mark Brown, Bill White, Adam Demner,, Erin Bostic,, Yu Wang and the rest of the WBL and SWS Any Questions? 11