Glebe Branch Stream Restoration (Glebe Creek) South River Watershed Project No. B559700 Contract No. B559701

GLEBE BRANCH STREAM RESTORATION (GLEBE CREEK) SOUTH RIVER WATERSHED PROJECT NO. B559700 CONTRACT NO. B559701

Watershed and Site Assessment Report

December 2016

Prepared For: Anne Arundel County Department of Public Works Watershed Protection & Restoration Program 2662 Riva Road Annapolis, MD 21401

Prepared by: Biohabitats, Inc. / Century Engineering, Inc. A Joint Venture

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Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW

Table of Contents 1 Introduction ...... 1 1.1 Project Study Area and Background ...... 1 1.2 Project Goals and Objectives ...... 3 2 Environmental Resources Inventory ...... 3 2.1 Overview of Assessment Methods ...... 4 2.2 Stream Classification ...... 4 2.3 Watershed Characterization ...... 4 2.4 Historic and Present Land Use ...... 5 2.5 Geology and Soil ...... 5 2.6 Wetlands and Surface Waters ...... 7 2.7 Preliminary Hydrology ...... 8 2.8 Riparian Vegetation ...... 9 2.9 Biological and Cultural Resources ...... 10 3 Constraints Analysis ...... 10 3.1 Limited Environmental Assessment ...... 10 3.2 Existing Utilities and Infrastructure ...... 1 1 3.3 Forest Impacts ...... 14 3.4 Property Ownership, Easements, and Construction Access Opportunities ...... 14 3.5 FEMA Floodplain and Hydrologic Trespass ...... 15 3.6 Forest Conservation Priority Areas ...... 16 3.7 RTE and In-Stream Work Restrictions ...... 16 4 Reference Reach Characterization ...... 16 5 Existing Stream Conditions ...... 17 5.1 Site Assessment ...... 17 5.2 Stream Geomorphology ...... 17 5.3 Stream Stability Evaluation ...... 26 5.4 Bank Stability Analysis and Erosion Estimate ...... 29 6 Preliminary Conceptual Design ...... 31 6.1 Restoration Approach Alternatives Analysis ...... 31 6.2 Restoration Techniques ...... 32 6.3 Approaches by Reach ...... 34 6.4 Roadway Culvert Analysis ...... 4 3 6.5 Stormwater Management Basin D1 Analysis ...... 45 6.6 Functional Assessment and Ecological Uplift Evaluation ...... 47 6.7 Water Quality Credits ...... 48 6.8 Recommendations ...... 49

Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW

6.9 Future Design Development ...... 49 7 References and Correspondence ...... 51 7.1 References ...... 51 Appendix A: Existing Conditions and Drainage Area Map, Geomorphic Assessment Data And Soils Report Appendix B: Historical Imagery and Mapping Appendix C: Natural Resource Inventory Report Appendix D: Agency Correspondence Letters Appendix E: As Built Drawings Appendix F: Reference Reach Search Appendix G: Photographic Log7 Appendix H: SEM Model Tables Appendix I: BANCS Results Appendix J: Roadway Culvert Analysis Appendix K: SWM Basin D1 Analysis Appendix L: Functional Assessment Tables

List of Figures: Figure 1: Project Location Map Figure 2: FEMA FIRM Map Figure 3: Stream Evolution Model (SEM)

List of Tables: Table 1: Soil Map Units and Associated Hydric Soil Components Table 2 Stream Stats Flow Statistics Table 3 Stream Segments Table 4: Geomorphic Data and Stability Summary Table 5: Bankfull Region Regression Results Table 6: Summary of BEHI predictions Table 7: Stormwater Management Basin Analysis Results Table 8: Pond Inflow Rates for 2-year, 10-year, and 100-year storms Table 9: Pond Outflow Rates for 2-year, 10-year, and 100-year storms Table 10: Removal Rate Predictions

Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW

1 INTRODUCTION

1.1 Project Study Area and Background The Anne Arundel County (County), Maryland, Watershed Preservation and Restoration Program (WPRP) is initiating the development of projects that were identified in the comprehensive assessment of the South River Watershed. These projects are being implemented to provide ecological enhancement and support the requirements of the National Pollutant Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) permit issued to the County by the Maryland Department of the Environment (MDE) and to assist the County in meeting pollutant load reductions associated with the Chesapeake Bay Total Maximum Daily Load (TMDL).

The stream under evaluation, referred to as Glebe Branch by the County for this project, but known as multiple names (Glebe Creek on some mapping and West Glebe Branch on development stormwater as built plans) begins as one of the headwater branches to the tidal portion of Glebe Creek. Its origin is located within the South River Colony Golf Course Community at the northeast side of Antiqua Place. The evaluation reach continues in a northeasterly direction, crossing under several roads including Colony Crossing Road, Central Avenue East (MD 214) and Mayo Road (MD 253), before ending at the tidal water confluence of Glebe Creek. These stream segments collectively comprise an estimated 8,500 linear feet of degraded channels within approximately 48 acres of stream valley, referred to throughout this report as the Study Area and illustrated in Figure 1. This full length was evaluated as part of the site assessment, but the length of stream below Mayo Road was not included in the preliminary conceptual designs per County direction because it was determined to not warrant restoration. The project Study Area is approximately 48 acres (see Figure 1).

Figure 1: Project Location Map

1.2 Project Goals and Objectives The stream restoration design work entails preliminary environmental analysis and feasibility study, field surveys, preliminary and final design, permitting, acquisition of easements, and construction documents. The design goals for this project are:

1. Provide stream valley restoration, including the re-connection of the stream channel with riparian wetlands and optimizing floodplain reconnection of stormflows. 2. Provide design features that promote denitrification during base flow. 3. Provide significant reduction in annual mass of sediments and attached nutrients originating from on-site channel degradation and upstream loss being delivered to downstream receiving waters. 4. Enhance stream and riparian ecological functions. 5. Provide an integrated stabilization approach to all storm drain outfalls within the Project Limits. 6. Document water quality (and/or other) credit towards Anne Arundel County’s National Pollutant Discharge Elimination System (NPDES) municipal separate storm sewer system (MS4) permit watershed restoration requirement, and assist in meeting Anne Arundel County’s waste load allocation towards the Chesapeake Bay Total Maximum Daily Load (TMDL).

The goal of the Watershed and Site Assessment Report is to identify and describe watershed and site resources, as well as the cause and consequences of the impairments to both the watershed and the impaired stream reach(s) (see Harman and Starr 2011). The Watershed and Site Assessment Report also present evaluation and discussion of preliminary design concept alternatives; one of which will be selected for further evaluation in the subsequent Schematic Design task.

2 ENVIRONMENTAL RESOURCES INVENTORY

Understanding the existing conditions within a stream and its watershed is critical for providing context for project work, determining dominant physical processes, identifying specific stream stability issues, and formulating an appropriate restoration strategy.

This section briefly describes assessment methods and results related to the physical setting, geology, soils, land cover, land use, urban infrastructure, and hydrology within the watershed. As described below, this information was compiled from existing Geographic Information System (GIS) layers, orthophotography, and field observations.

The Glebe Branch watershed and the surrounding area has undergone a series of changes typical of developed Anne Arundel County. Following rural colonial settlement, the area was deforested and transitioned to agricultural land use, followed by urbanized residential development with and without the installation of adequate stormwater management devices. The historic land use changes and current urbanized conditions are causing predictable impacts to the stream network within the watershed and the project Study Area. Stream conditions throughout the Study Areaare variable and described on a reach-by-reach basis later in this report.

2.1 Overview of Assessment Methods Desktop analyses primarily utilized orthophotography, existing geographic information system (GIS), and other watershed data available from various sources. GIS data for the full watershed area were downloaded online from Anne Arundel County’s County Maps & GIS Data. This data included impervious polygons (roads, driveways, sidewalks, and buildings), and utilities information (e.g., storm and sanitary sewers, manholes, and outfalls). Soils data were obtained from the Natural Resource Conservation Service’s (NRCS) Web Soil Survey available online. Geologic and land use GIS mapping was obtained from the US Geological Survey and Maryland Department of Planning, respectively. LIDAR elevation data was downloaded from MD iMap.

Base mapping for the project was created for the immediate stream corridor with GIS and LIDAR derived topography for surrounding areas within the watershed. Final base mapping, which includes detailed property ownership information, is shown in Appendix A. Initial field investigations were conducted by the Biohabitats / Century Engineering Joint Venture field crews during the late spring of 2016. Investigations within the Study Area included a general reconnaissance, a geomorphic channel assessment, and characterization of bank conditions, wetland delineation, and riparian vegetation survey. Wetland and tree delineations were located using Global Positioning System (GPS) on June 27, 2016 an SXBlue GPS receiver.

Specific protocols and methods utilized for each type of assessment are discussed in the sections that follow. Mapping showing existing conditions through the project Study Area is included in Appendix A, with more detailed information about the mapped features included throughout this report.

2.2 Stream Classification Glebe Branch is located within the South River watershed (MD 8-digit Basin Code 02131003). The Maryland Department of the Environment (MDE) has identified Glebe Branch as a Use Class I waterway.

As Class I waterway, in-stream work may not be conducted March 1 through June 15.

2.3 Watershed Characterization Glebe Branch originates within the South River Colony Golf Course Community and flows through private and County owned properties to its terminus at Glebe Bay in Anne Arundel County within the Coastal Plain physiographic province.

Preliminary watershed data for Glebe Branch, calculated using StreamStats, resulted in a drainage area of 0.76 square miles. The project drainage area is located in Edgewater, Anne Arundel County and a drainage area map is included in Appendix A. The drainage area is generally of low topographic relief that gently slopes east, becoming relatively featureless lowland terrain in the vicinity of Glebe Branch. The upstream portion of the watershed consists of residential neighborhoods and the golf course community before continuing downstream of Colony Crossing where the valley widens to wooded, floodplain and floodplain terrace to its terminus with Mayo Road (MD 253). The basin morphology is a valley type VIII Alluvial Gulch Fill C-AL-AD and U-AL-AD depending on the degree of confinement within each reach (Rosgen, 2016). The Study Area is a small order stream located on alluvial fill within a narrow

© Biohabitats, Inc 4 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW valley widths that confines the stream in some locations due the manipulated anthropogenic changes.

Climate within the region is strongly influenced by the Chesapeake Bay, resulting in a subtropical climate with hot, humid summers and cool winters (MSA, 2016). The average annual temperature, as recorded at BWI, ranges from 75°F to 35°F with highs averaging 85°F in summer and 44°F in winter. Average annual precipitation is 40.76 inches, most of which falls during the spring and summer months resulting from frequent thunderstorms (MSA, 2016).

2.4 Historic and Present Land Use Significant changes have occurred to the watershed over the last 100+ years, some of which were identified using historical imagery (See Appendix B – Historical Imagery and Mapping).

A comparison of the available historical data within the Study Area watershed shows a much different landscape than today. It consisted of few roadways outside of the main travel routes, such as Solomons Island Road (MD Route 2) and Central Avenue (MD 214), as far back as the late 1800s. These travel routes were likely surrounded by agriculture and wooded areas. Based on USGS historical aerial imagery, much of the Glebe Branch watershed remained wooded until the mid to late 1970s when Central Elementary School, South River High school, and the Central Special School were constructed. Glebe Branch may have been relocated away from the center of the valley and confined to its present location to make room for these new facilities. In the 1994 Google Earth historical aerial, drastic changes in the watershed begin to appear with the construction of the South River Colony Golf Course Community, the South River Colony Shopping Center, and associated stormwater management facilities. Culvert crossings installed for Colony Crossing, Central Avenue, Mayo Road, and a dirt access road to Central Elementary School currently provide grade control through the reaches and have influenced the channel morphology as discussed in the existing stream conditions section..

Prior to the availability of historical imagery, it is likely the channel was stable, with a periodically wet valley bottom that did not have a defined single thread channel. Base level or profile controls that would have prevented head cuts and gully formation would have included some or all of the following conditions: fallen woody material scattered across the valley bottom, extremely shallow low stress flood flows, and extensive herbaceous vegetation with rooting depths and densities capable of preventing any incision or channelization within the valley bottom. Traces of these types of historic features or characteristics were not found at the project site and thus the channel was likely not in its present location, but ditched or relocated at some point towards the southeast of the valley.

2.5 Geology and Soil The Study Area and vicinity is located within the Atlantic Coastal Plan Province. Specifically, the portion of the project Study Area upstream of Central Middle School is located within the Western Shore Uplands Region and downstream of Central Middle School is located within the Western Shore Lowlands Region (Maryland Geological Survey 2008). The Western Shore Uplands Region is bounded by the Western Shore Lowlands Region, which consists of fluvial and estuarine terraces, marshes, and drowned mouths of rivers draining into the Chesapeake Bay and Potomac estuary system. Geology within the project Study Area consists of the Nanjemoy and Aquia Formation within the Pamunkey Group. These formation consists of dark- green to gray green well sorted fine to medium grained sand. The Nanjemoy Formation also

© Biohabitats, Inc 5 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW contains plastic clay and local lenses of very fine-grained white sand from 0 to 30 feet The Aquia Formation is unstable at steeper slopes. Both the Aquia and Nanjemoy formations are known for forming acid sulfate soils when the glauconite-bearing layers are exposed. Soils in the area will be slightly acidic due to this geology.

According to the Soil Survey of Anne Arundel County, Maryland (United States Department of Agriculture-Soil Conservation Service [USDA-SCS], 2011) and more recently available Natural Resources Conservation Service Soil Survey Geographic Database (NRCS SSURGO) digital soil data for the county (NRCS Web Soil Survey, 2010), the predominant soil associations found within the vicinity of the study area is the Monmouth-Collington Association. Soil associations provide a general idea of the soils in a county’s landscape, but is not suitable for planning and management. Soils in the Monmouth-Collington Association are well-drained, sandy and loamy soils that develop in sediments containing glauconite. For planning and management purposes, the soil survey with the delineated soil map units, a collection of areas defined in terms of their similar components, should be referenced. Based on the Web Soil Survey, 16 soil map units are delineated within the study area and are identified as (Soil Survey Staff, 2016):

 Adelphia-Holmdel complex, 2-5% slopes (AdB)  Annapolis loamy sand, 2-5% slopes (AoB)  Annapolis fine sandy loam, 5-15% slopes (AsC)  Annapolis fine sandy loam, 15-25% slopes (AsE)  Annapolis-Urban land complex, 0-5% slopes (AuB)  Colemantown fine sandy loam, 0-2% slopes (CkA)  Colemantown silt loam, 0-2% slopes (CmA)  Colemantown-Urban land complex, 0-5% slopes (CnB)  Collington-Wist complex, 2-5% slopes (CoB)  Collington-Wist complex, 5-10% slopes (CoC)  Collington and Annapolis soils, 10-15% slopes (CRD)  Donlonton fine sandy loam, 0-2% slopes (DnA)  Donlonton fine sandy loam, 2-5% slopes (DnB)  Donlonton-Urban land complex, 0-5% (DuB)  Urban land (Uz)  Widewater and Issue soils, 0-2% slopes, frequently flooded (WBA)

The Hydric Soils List – All Components (Soil Survey Staff, 2016) identifies soil map units with major or minor hydric soil components. The table below summarizes the soil map units within the study area and their associated hydric components, if applicable. A copy of the Web Soil Survey report and map for the study area is included in Appendix A.

Table 1: Soil Map Units and Associated Hydric Soil Components

Soil Soil Component Map that is Hydric Component Percent Hydrologic Soil Map Unit Name Unit that is Hydric Soil Group Symbol Adelphia-Holmdel Shrewdbury 5 C AdB complex, 2-5% slopes Annapolis loamy sand, 2- NA N/A C AoB 5% slopes Annapolis fine sandy N/A N/A C AsC loam, 5-10% slopes Annapolis fine sandy Widewater 5 C AsE loam, 15-25% slopes Annapolis-Urban land N/A N/A C AuB complex, 0-5% slopes Colemantown fine sandy Colemantown 80 C/D CkA loam, 0-2% slopes Shrewsbury 10 Keansburg 5 Colemantown silt loam, Colemantown 80 C/D CmA 0-2% slopes Shrewsbury 10 Keansburg 5 Colemantown-Urban land Colemantown 45 C/D CnB complex, 0-5% slopes Keansburg 5 Collington-Wist complex, N/A N/A B CoB 2-5% slopes Collington-Wist complex, N/A N/A B CoC 5-10% slopes Collington and Annapolis N/A N/A B CRD soils, 10-15% slopes Donlonton fine sandy Colemantown 5 D DnA loam, 0-2% slopes Donlonton fine sandy Colemantown 5 D DnB loam, 2-5% slopes Donlonton-Urban land Colemantown 5 D DuB complex, 0-5% Uz Urban land N/A N/A D Widewater and Issue Widewater 40 C/D soils, 0-2% slopes, Zekiah 10 WBA frequently flooded Longmarsh 5 Shrewsbury 5

2.6 Wetlands and Surface Waters

A wetland delineation was performed within the approximately 48 acre Study Area, consisting of relatively flat, densely forested, land bisected by Glebe Branch.

One (1) perennial stream, Glebe Branch, was identified within the Study Area. Thirteen additional intermittent channels, and one (1) ephemeral drainage channel were delineated on- site. The intermittent tributaries within the Study Area exhibit seasonal flow, receive flow from adjacent wetlands, and convey flow from overland flow toward Glebe Branch. Twenty-six palustrine wetland systems were identified within the project Study Area. Twenty-five of the 26 delineated wetland are under forest canopy. One (1) wetland system was identified on non- forested property owned by the South River Golf Course, which consisted of maintained herbaceous and scrub-shrub vegetation. One (1) historic wetland was identified within the study area. See Appendix C for wetland locations shown on Natural Resource Inventory mapping.

Soils Soil profiles were conducted to a depth of 18-22 inch, barring refusal, within the sampled wetland and upland areas. A maximum of three (3) horizons were identified within the profile. Hydric soil indicator Depleted Matrix (F3) was met at all wetland sample plots. Upland soils typically consisted of bright soils with no redoximorphic features.

Hydrology Surface water, high water table, and saturation were observed at a majority of the delineated wetland systems. The twenty-six delineated wetland systems displayed multiple primary and secondary wetland hydrology indicators, including but not limited water-stained leaves (B9), inundation visible on aerial imagery (B7), hydrogen sulfide odor (C1), sparsely vegetated concave surface (B8), drainage patterns (B1), saturation visible on aerial imagery (C9), and geomorphic position (D2). Upland sample plots did not satisfy the wetland hydrology criterion.

Vegetation The sample site was in a forest community encompassing the entire Study Area. The species observed were typical of the vegetation community type and included the following: red maple (Acer rubrum), tulip poplar (Liriodendron tulipifera), American sycamore (Platanus occidentalis), spicebush (Lindera benzoin), Jack-in-the-pulpit (Arisaema triphyllum), and jewelweed (Impatiens capensis). The majority of the Study Area consisted of healthy mid-successional forest with minimum to moderate human disturbance. Noxious and non-native species identified with the area include poison ivy (Toxicodendron radicans), Japanese honeysuckle (Lonicera japonica), and Tartarian honeysuckle (Lonicera tatarica).

The hydrophytic vegetation criterion was satisfied within all wetland sample plots. The majority of upland sample plots did not satisfy this wetland criterion.

Refer to the Glebe Branch Restoration Project Natural Resource Inventory Report in Appendix C for more detailed information regarding the delineated wetland, ephemeral, intermittent and perennial stream channels, and forest stand delineation. At this time, Waters of the US is delineated as a single center line, but will be more clearly defined using the topographic survey once it is obtained to identify lateral extents.

2.7 Preliminary Hydrology A complete hydrologic analysis was not conducted as part of this submittal. Preliminary estimates of peak flows were determined using StreamStats (2012) to the downstream limit of the Study Area and are presented in the table below.

Table 2 Stream Stats Flow Statistics

Peak Discharge Storm Event (ft3/s) 2 yr. 193 5 yr. 375 10 yr. 561 25 yr. 918 50 yr. 1280 100 yr. 1770

Several offline water quality ponds and one in-line peak management pond were noted during the initial assessment and are described below in section 3.2 along with the descriptions of the contributing outfalls. The stream segments included in this project are included in Table 3.

Table 3 Stream Segments

Flow Stream Use ID # Stream Order Regime Designation GC1011 (Glebe Branch) Perennial 2nd Use 1 GC1010 (Glebe Branch) Perennial 2nd Use 1 GC1009 (Glebe Branch) Perennial 2nd Use 1 GC1008 Intermittent 1st Use 1 GC1007 Intermittent 1st Use 1 GC1006 Intermittent 1st Use 1 GC1001 Perennial 2nd Use 1

2.8 Riparian Vegetation The majority of the Study Area is forested with the exception of a few extensions along the Study Area including a depressional feature along the adjacent South River Golf Course, and multiple residential properties that are immediately outside the dripline of the on-site forest. These areas are dominated by maintained lawn and landscape cultivar tree and shrub species. Nine (9) forest stands were identified within the project Study Area. The nine (9) stands were healthy, mixed hardwood mid-successional stands that displayed low quantities of invasive species, good forest structure, and function as a wildlife corridor. Minimum to moderate human impact was observed within the tree lines of these stands. The linear forested region encompassing the nine (9) identified stands is bound by the South River Golf Course and Central Elementary and Special Schools to the west and northwest, and by residential properties and South River High School to the south and southeast.

The plant community along the southwestern portion of the study area, from Antiqua Place to Colony Crossing, consists of a mid to late-successional mixed hardwood forest. The canopy is dominated by red maple, sweetgum, tuliptree, American sycamore, and American beech. The understory species consists of northern spicebush, red maple, and multiflora rose. The woody vines within the southwestern portion include round-leaf greenbrier, poison ivy, and Japanese honeysuckle. The herbaceous layer consists of jewelweed, sensitive fern, green arrow-arum, reed canary grass, and May-apple.

The plant community within the middle section of the study area, from Colony Crossing to MD 214 (Central Avenue East), consists of a mid to late-successional mixed hardwood forest. The is dominated by red maple, American elm, sweetgum, tuliptree, white oak, American beech, ironwood, and American sycamore. The common understory species are spicebush, multiflora rose, red maple, Japanese privet, American holly, maple-leaf viburnum, and black cherry. The herbaceous layer, which is moderately spread, is dominated jack-in-the-pulpit, hayscented fern, Christmas fern, and May-apple. The dominant woody vines are common greenbrier, Virginia creeper, poison ivy, fox grape, English ivy, and Japanese honeysuckle.

The plant community along the northeastern portion of the study area, from MD 214 (Central Avenue East) to Mayo Road, consists of a mid to late-successional mixed hardwood forest. The dominant tree species are river birch, mockernut hickory, northern red oak, southern red oak, red maple, green ash, and sweetgum. The understory is dominated by American beech, flowering dogwood, multiflora rose, American holly, serviceberry, spicebush, American elm, white ash, American sycamore, tuliptree, highbush blueberry, white oak, and mockernut hickory. The herbaceous layer is dominated by May-apple, jewelweed, sensitive fern, Japanese privet, shallow sedge, Jack-in-the-Pulpit, and goosegrass. The dominant woody vines are common greenbrier, fox grape, Japanese honeysuckle, poison ivy, and Virginia creeper.

2.9 Biological and Cultural Resources Letters were sent to the US Fish and Wildlife Service (USFWS) Office of Endangered Species (OES), the Maryland Department of Natural Resources (MD DNR) Wildlife and Heritage Service, and the Maryland Historical Trust (MHT)/MDSHPO. These letters inquired about the presence of rare, threated, and endangered species as well as historic resources within the Study Area in February 2016.

On February 25, 2016 the USFWS determined there are no listed species or critical habitats identified within the vicinity of the project Study Area.

MD DNR Fisheries responded on May 31, 2016 that Glebe Branch (West Chesapeake Bay Basin) and tributaries near the Study Area are classified as Use I streams (Water Contact Recreation, and Protection of Aquatic Life). Glebe Branch (West Chesapeake Bay Basin) and tributaries near the Study Area are classified as Use II streams (Shell Fish Harvesting Waters). Yellow perch (Perca flavescens) and white perch (Morone americana) have been documented near the project Study Area. Where the presence of yellow perch has been documented, generally no instream work is permitted in Use I and Use II streams during the period of February 15 through June 15, inclusive, during any year. Where the presence of white perch has not been documented, no instream work is permitted from March 1 through June 15, inclusive, during any year. MHT responded on March 21, 2016 that there are no historic properties in the area of potential affect. See agency correspondence letters in Appendix D.

3 CONSTRAINTS ANALYSIS

3.1 Limited Environmental Assessment A limited desktop environmental due diligence report of the Study Area has been performed to document the findings of present and past Study Area uses relative to the potential contamination of properties on and nearby the stream alignment, and identify areas of potential

© Biohabitats, Inc 10 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW concern. The environmental risk of the Study Area was evaluated through a review of records and pertinent information. This information can be found in the Glebe Branch - Stream Restoration Limited Environmental Assessment Report (November 2016).

3.2 Existing Utilities and Infrastructure 3.2.1 Roadway Culvert Crossings

A primary site constraint impacting the stream throughout the project is driven by the existing utilities and infrastructure within the Study Area. The various roadway culvert crossing elevations were likely lowered below historic channel elevation to fit the original culvert or during the replacement of an undersized culvert to maximize the conveyance capacity. Significant changes to the culvert tie in elevations may not be feasible unless the entire crossing structure and possibly roadway profile is changed; thus making the existing crossing elevations a difficult site constraint to contend with during design. The evaluation of crossing upgrade feasibility and cost is found in Section 6.4 below.

 Colony Crossing Culvert – This roadway crossing consists of a 60-inch RCP principle spillway pipe associated with SWM Basin D1 described in Section 3.2.3 below.  Unnamed Road at School - Twin 54-inch CMP culverts convey Glebe Branch from southwest to northeast under an unnamed road to Central Elementary School and Central Special School.  Central Avenue (MD 214) - One 66-inch x 33-inch CMP culvert conveys Glebe Branch from southwest to northeast under Central Avenue (MD 214).

3.2.2 Water Quality Ponds Several private water quality pond outfalls, as identified in the South River Colony Parcel D Storm Drain as built plans, discharge either directly to the stream channel or via an armored channel. The pond embankments have caused some impacts to the width of the active floodplain and the stream channel enlargement has damaged pond infrastructure. Without further analysis of the original pond design and site constraints, the elevations of pond outfall structures are assumed to not be significantly modified for this project, potentially limiting channel tie in elevations at these locations. This analysis of water quality pond retrofit opportunities has not been requested by the County at this time. See available as-built drawings in Appendix E and locations on Geomorphic Assessment Map (Appendix A).

 South River Colony Water Quality Pond #7 (Appaloosa Way) – This pond is located on the south side of the channel and receives flows diverted from the storm drain system prior to outfall P25O015. The pond outfall protection has been damaged within the existing channel. The footprint of the pond takes up approximately two-thirds of the floodplain width at this location, causing significant channel confinement. Also, it appears the pond embankment has been partially breached, possible due to a past blockage at the riser. A pond inspection is recommended.  South River Colony Water Quality Pond #5 (Hunt Club) – The pond is located on the south side of the channel. The outfall protection has been damaged within the existing channel (P25O011). The footprint of the pond takes up a small portion of the floodplain width at this location, causing some channel confinement. Streambank erosion has caused significant damage to the downstream side of the pond embankment.  South River Colony Water Quality Pond #1 (on golf course across from Sewall Court) – The pond is located on the north side of the channel and has no visible inflow structures, but receives flows diverted from the storm drain prior to outfall P24O021. No as-built

drawings have been located, but it is shown on South River Colony Parcel D SWM plans as an existing pond constructed under GP2004645 and labeled “WQP#1”. The pond outfall ends at the same headwall as outfall P24O021, which is located at the stream invert elevation and has a large scour hole below the structure.  South River Colony Water Quality Pond #2 (downstream of Colony Crossing) – The pond is located well above the stream and has a stable rip rap outfall channel running along the toe of Colony Crossing road embankment. This pond presents no site constraints because it is located well above the stream valley.

3.2.3 Stormwater Management Ponds Two Stormwater management ponds are located within or adjacent to the study area. The first is an in-line pond that is located within the Study Area at Colony Crossing and may be directly impacted by the project. The second is a large retention pond that is located outside but adjacent to the Study Area, and will not be impacted by the project. Without further analysis of the original pond design and site constraints, the elevations of pond outfall structures are assumed to not be significantly modified for this project, potentially limiting channel tie in elevations at these locations. See available as-built drawings in Appendix E and locations on Geomorphic Assessment Map (Appendix A).

Significant changes to the pond riser and spillway may not be feasible unless the entire pond configuration is changed; thus making the existing in-line pond a difficult site constraint to contend with during design. The evaluation of pond retrofit feasibility and cost is found in Section 6.5 below.

 SWM Basin D1 (Colony Crossing) - A private, in-line stormwater management basin (South River Colony Parcel D SWM Basin D-1) located just upstream of Colony Crossing is providing some level of flow attenuation to the downstream reaches. The 12 inch low flow pipe is blocked by sediment trapped within the stream channel leading to it, with no visual evidence of the low flow structure except for the top of the headwall and a small amount of flow pushing through the blockage. The pond basin appears to have deposited a significant amount of sediment generated from the upstream channel erosion, and has likely lost a significant portion of the storage volume. The Colony Crossing Roadway is acting as the pond embankment, but based on a-built plans it does not appears to meet MD 378 criteria of 3 feet of freeboard above the 100 year water surface elevation for a roadway embankment. Altering the pond configuration may be limited based on physical and budget limitations to riser and embankment modification and its impact to peak flows to the downstream reaches.  South River Colony Parcel A Commercial Complex Quantitative SWM Retention Pond (Lake) – The pond is owned by Anne Arundel County and is located between MD 214 and Mayo Road and outfalls via twin 8 foot by 5 foot box culverts (Q24O013) onto a stable rip rap outfall channel.

3.2.4 Storm Drain Outfalls Below is an inventory and description of the storm drain outfalls contributing to the stream channel within the Study Area based on visual assessment, County GIS data and available as- built plans. The elevations of these storm drain outfall structures are assumed to not be significantly modified for this project, potentially limiting channel tie in elevations at these locations. See available as-built drawings in Appendix E and locations on Geomorphic Assessment Map (Appendix A).

 P25O007 – 15” RCP Anne Arundel County outfall receiving drainage from Antiqua Place. Outfall protection is stable and the outfall presents no site constraints to the design.  18” HDPE – This outfall is not within the County GIS system, but is a stable outfall from the golf course protected with rip rap. It presents no site constraints to the design because it is located well away from the existing stream channel.  P25O015 – 36” RCP Anne Arundel County outfall off of Appaloosa Way receiving drainage from Colony Crossing. Outfall protection and flow path to the stream is stable and presents no site constraints to the design because it is located well away from the existing stream channel.  P25O008 – The storm drain network here appears to be shown incorrectly on County GIS. The outfall structure off of Colts Neck Ct could not be located in the field, but appears to be routed to the Hunt Club Water Quality Pond 5 per the South River Colony Parcel D Storm Drain as-built drawings and presents no site constraints to the design. It enters the stream channel at outfall structure P25O011.  P25O020 – The storm drain network here appears to be shown incorrectly on County GIS. The outfall structure off of Dark Star Ct could not be located in the field, but appears to be routed to the Hunt Club Water Quality Pond 5 per the South River Colony Parcel D Storm Drain as-built drawings and presents no site constraints to the design. It enters the stream channel at outfall structure P25O011.  Private 30 inch CMP – An outfall from the large golf course pond in front of the clubhouse periodically receives flows from irrigation system and periodically discharges to the stream valley. The pond is a reservoir for the golf course irrigation system, the pond is recharged with groundwater pumping. Visual observations indicate a large volume of flow with high velocities is generated during these discharge events, causing a large headcut formation downstream of outfall within the channel from the outfall to the stream. Stabilization of this outfall channel should be addressed by the stream restoration design.  P240021 – Two Anne Arundel County pipes coming from the storm drain network off Colony Crossing across the golf course and Water Quality Pond #1 riser enter the stream at this single headwall. The outfall is located at the stream invert elevation and the protection has been scoured out and pushed into stream channel, leaving the headwall structure undermined.  P24O026 – 15 inch RCP Anne Arundel County outfall receiving drainage from Colony Crossing. Outfall protection is stable and the outfall presents no site constraints to the design.  P24O017 – 60 inch RCP Anne Arundel County culvert outfall under Colony Crossing. Rip rap outfall protection is stable until it ends at a sewer crossing. Below this sewer crossing is large channel headcut, with the stream channel several feet lower than the protection. The elevation of this outfall presents a site constraint to the stream restoration design.  P24O025 - 15 inch RCP Anne Arundel County outfall receiving drainage from Watkins Row and a private golf course pond. Outfall protection is unstable and the receiving channel is severely downcut. Stabilization of this outfall channel should be addressed by the stream restoration design.  P24O007 – 30 inch RCP Anne Arundel County outfall receiving drainage from the Center of Applied Technology South parking lot and adjacent roadway. Minor bed scour and bank erosion is located immediately downstream of the outfall. While the outfall appears to be stable in its current condition, a water quality feature may be added as part of the proposed design.

 Q24O013 – Twin 8 foot x 5 foot box culverts owned by Anne Arundel County drain from a riser structure in the South River Colony A Commercial Complex Quantitative SWM Pond. The outfall protection is stable and presents no site constraints to the design.  Q24O019 – 16 inch DIP Anne Arundel County culvert conveys flow under Bass Pond Walkway adjacent to the South River Colony A Commercial Complex Quantitative SWM Pond. The outfall protection is stable and the outfall presents no site constraints to the design.  Q24O008 – 21 inch CMP Anne Arundel County culvert that outfalls into Glebe Branch, south of Shore Drive. The outfall receives drainage from the adjacent residential neighborhood to the north. Minor displacement of the outfall protection has occurred and geotextile is exposed. No work is proposed below Mayo Road based on discussions with the County.

3.2.5 Utilities There is a sanitary sewer crossing located approximately 60 feet below the Colony Crossing culvert outfall. The elevation of the crossing appears to be several feet below existing grade, as shown on the South River Colony Parcel D Water and Sewer Plans. See available as-built drawings in Appendix E. The elevation of the crossing will be confirmed once survey is obtained but does not appear to be a significant site constraint. Underground utility designation and site survey have yet to be performed to confirm presence and location of other utilities such as power, gas, and electric.

3.3 Forest Impacts The site is located primarily within a forested riparian area (see Section 2.8 above) owned mostly by Anne Arundel County, with the upper limits owned by Friendswood Development Co/South River Colony HOA. Although some impacts to the forest canopy are unavoidable with this type of project and should not solely drive design decisions, the restoration approaches have been developed to minimize impacts to this resource. Tree loss can result in loss of habitat and its impact to visual buffers can be a concern to the private stakeholders such as the golf course and adjacent residential properties.

3.4 Property Ownership, Easements, and Construction Access Opportunities The Study Area is located on property owned mostly by Anne Arundel County, with the upper limits owned by Friendswood Development Co/South River Colony Home Owners Association HOA, see Figure 1 and Concept Plans. Private ownership extends a little over 1000 feet downstream of the Antiqua Place storm drain outfall. Upstream of Colony Crossing, construction access opportunities for reaches 1 through 4 (see Section 5.2.2 for reach descriptions and Concept Mapping), on the south side of the project Study Area, is limited to narrow existing storm drain easements between homes, due to the presence of residential development. Access could also be gained via an undeveloped area at the upstream end of the project just off Antiqua Place, but this available area will be limited due to the wetland area. It is possible a golf course path in the area could be followed until an unobstructed path is found to the stream channel, but this would need to be vetted with the South River Colony Golf Club.

The north side of the project along reaches 1 through 4 is bordered completely by the South River Golf Club. The County Project Manager, James Woods, met with the Club General Manager, John Berish, on June 2, 2016. The club is open to allowing construction access through the course at selected areas from November through February, with March available for

© Biohabitats, Inc 14 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW cleanup and grass re-establishment. The two areas of potential golf course access are across hole #10 fairway and hole #18 fairway (as shown on concept drawings). The fairway at hole #10 is ideal, with minimal length of crossing, and it is out of the "landing area" of drives off the #10 tee. It has minimal impact to other club facilities. Access across hole #18 fairway would have to wind around the maintenance building, where little width is available. There is a longer path through the driving range that may be a future consideration.

Use of the parking lot as a staging and stockpile area will not be allowed by the club. Mr. Berish suggested asking the HOA to use the community pool parking lot across the street, which is likely not used in the late Fall/Winter. This will require future coordination between the County and the HOA.

Potential Reach 5 access is located at the upstream and downstream end of the reach. Upstream access would be off of Colony Crossing on Golf Club property. Downstream access would be off of the Central Elementary School road crossing.

Project Reaches 6 and 7 are located entirely on Anne Arundel County Board of Education property with the exception of a 110 foot Maryland State Highway Administration (MSHA) right- of-way along MD 214. These reaches are located adjacent to Central Elementary School and the South River High School Ball Field. Access could be gained via a dirt road which crosses over Glebe Branch between Central Elementary School and the Center of Applied Technology. Considerations may have to be made to accommodate school schedule and activities. Reaches 8 and 9 are located on Anne Arundel County property designated as floodplain with a 50 foot right-of-way located along Mayo Road. Access will likely be off of Mayo road along an existing trail across the embankment

3.5 FEMA Floodplain and Hydrologic Trespass Detailed HEC-RAS analysis will be performed in future submittals as the design progresses. An existing FEMA floodplain was identified downstream of Mayo Road (see Figure 2), however based on the existing conditions assessment no work has been proposed in this area.

Figure 2: FEMA FIRM Map

3.6 Forest Conservation Priority Areas At this time no forest conservation areas have been identified.

3.7 RTE and In-Stream Work Restrictions There are no listed species or critical habitats identified within the vicinity of the project Study Area. Glebe Branch (West Chesapeake Bay Basin) and tributaries near the Study Area are classified as Use I streams (Water Contact Recreation, and Protection of Aquatic Life). Glebe Branch (West Chesapeake Bay Basin) and tributaries near the Study Area are classified as Use II streams (Shell Fish Harvesting Waters). Yellow perch and white perch have been documented near the project Study Area. Where the presence of yellow perch has been documented, generally no instream work is permitted in Use I and Use II streams during the period of February 15 through June 15, inclusive, during any year. Where the presence of white perch has been documented, no instream work is permitted from March 1 through June 15, inclusive, during any year.

4 REFERENCE REACH CHARACTERIZATION

A search was performed to locate and collect information on appropriate local reference reaches within the same physiographic province. Two reaches were initially identified as possible references reaches for this project; the left fork of Jabez Branch from an Inter-County Connector (ICC) site search, and an unnamed tributary to the Severn River from the USFWS Western Coastal Plain Reference Reach Survey (Starr et al, 2010). The reference reach report included in Appendix F contains the geomorphic variables and reference reach data for

© Biohabitats, Inc 16 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW unnamed tributary to the Severn River that were found in the USFWS report. It also contains the assessment information, geomorphic variables, photographs and reference reach data for both the Upper and Lower Jabez Branch reaches collected and provided by Coastal Resources, Inc.

This data will be used along with evaluation of modeling results during future design task to establish a range of dimensionless ratios and morphological relationships to calculate the stable dimension, pattern, and profile variables.

5 EXISTING STREAM CONDITIONS

5.1 Site Assessment A site assessment was performed between April and early May 2016 to identify distinct reaches within the Study Area with representative conditions, document existing site conditions through the collection of channel survey data, document causes and extent of instabilities, site constraints, and qualitatively assess the potential to provide ecological uplift based on the hydrological and ecological characteristics of the site. This included the collection of site photos, the identification of infrastructure and stream channel geomorphic conditions, and a bank stability analysis. A map of the existing channel condition is found in Appendix A, along with the geomorphic cross sections surveyed. A photographic log of the project is found in Appendix G.

5.2 Stream Geomorphology Stream channel stability is often described as a long-term state of “dynamic equilibrium.” In such a state, a channel’s bed and banks maintain their dimensions, pattern, and profile indefinitely, through a sustained balance between aggradation and degradation processes, even while experiencing natural migration and adjustment.

The stream channel within the project limit is currently in a state of disequilibrium exhibiting high degrees of aggradation and degradation in various sections. Overall, the channel is unstable. Much of the channel’s length contains visible signs of high rates of adjustment including lateral migration against valley walls, toe slope failures, active headcutting, deep downcutting, and incision. These adjustments have created conditions that have greatly increased sediment supply via bank erosion, caused decreased downstream water quality, increased downstream aggradation impacts, and impacted infrastructure. Alterations to the natural hydrology of the system and the human alteration of the stream channel is often the root cause of instability and can set into motion a series of major, sometimes rapid, channel adjustments that can be very detrimental to a stream ecosystem.

A map of the existing channel condition is found in Appendix A. The project was broken into ten distinct geomorphic reaches. A geomorphic cross section (oriented in the downstream direction) and profile was surveyed at each study reach to document channel condition and Rosgen Level 2 stream classification. The longitudinal profile was measured up and downstream of the typical section for each Reach for a length of approximately 20 to 30 bankfull widths or at a defining stream bed riffle or an abrupt break in slope (such as woody debris), not the entire reach length. At each section, a Wolman pebble count of the existing channel substrate was performed. This data was processed and evaluated in The Reference Reach Spreadsheet (Mecklenburg 2006). The following sections describe the stream geomorphology in more detail.

With an initial map identifying potential locations for geomorphic study, Biohabitats walked the length of the stream. In general, the location of reach breaks is based on visually appreciable changes in drainage area (confluences) and other measurable changes in morphology including channel slope, substrate, incision, floodplain characteristics, valley condition, planform geometry, channel stability and manmade obstructions such as dams and road crossings. In the case of the Glebe Branch project Study Area, reach breaks were readily identified based on road crossings and significant headcuts. In general, identified reach lengths are at the scale of about 500 to 1000 feet in length.

In total, ten reaches were identified and are shown in Appendix A:  Reach 1-4: Upper Glebe Branch: Antiqua Place to Colony Crossing  Reach 5-7: Middle Glebe Branch: Colony Crossing to MD-214  Reaches 8-10: Lower Glebe Branch: MD-214 to tidal limits

5.2.1 General Conditions The project Study Area is located within the Western Coastal Plain physiographic province (Maryland Geologic Survey, 2008). During the field reconnaissance, field crews noted features, such as moderate to low channel slopes, steep valley walls, and streambed materials dominated by sand or silt/clay substrate, which are consistent with this setting. The moderate to low sloped channels are pool dominated with sporadic riffle/run formations mostly due to wood debris jams and associated scour pools. In most locations along the Study Area, the channel has downcut through the upper soil horizons and exposed clay or an iron-cemented sediment horizon, and is severely incised. The streams have low sinuosity and are mostly located in mature forest at the toe of the steep stream valley wall, which is likely a factor in the low radius of curvature.

Observations along the channel network suggest the flow regime is perennial throughout the project Study Area. The stream is fed by groundwater, which is preferentially discharged into the stream channel as surface flow at the bottom of the channel incision. In many cases along the Study Area, this down cut enters into the iron-cemented sediment horizon.

In general, conditions along the stream reaches are typical of degraded creeks in suburban Anne Arundel County. Changes in land use activities and stream valley disturbances are potential factors that influence the planform of the channels. Many streams have been straightened to allow for farming, development, and other such activities. The highly urbanized landscape is a “driver” of flashy streamflow characteristics. Resulting high flow velocities and shear stresses lead to ongoing bank erosion and associated threats to property and infrastructure. Left unresolved, these problem areas will worsen and require more intensive and expensive maintenance.

5.2.2 Reach Measurements and Descriptions Representative photographs of each reach are included in Appendix G. One representative channel cross section, longitudinal profile, and riffle pebble count was collected in the field within each designated reach to characterize the stream types using the Rosgen classification system (Rosgen, 1996). The representative reach section was taken at a typical riffle, with the riffle pebble count also used to represent the reach bed material as there is little sorting of material size along the stream bed.

Prior to the field assessment, bankfull regional curve data from the USFWS Chesapeake Bay Field Office (McCandless 2003) and the USGS Regional Curves for Stream in the Non-Urban, Non-Tidal Coastal Plain (Krstolic and Chaplin, 2007) was compiled to gain perspective of typical bankfull characteristics for channels in similarly sized watershed in the same regional setting. During the field survey, the bankfull elevation at each cross section was identified based on available field indicators and compared to the regional curve data. Bankfull elevations in the field was derived from all available indicators including depositional features, changes in bank angle, vegetation patterns, and scour lines. Because the study reaches are mostly severely incised channels with vertical banks, very few strong indicators are present.

The Mecklenburg spreadsheet (2006 version) was used to compile and graph cross sections, profiles, and channel substrate sizes from these field measurements and estimate discharges associated with the evaluated bankfull event. The Mecklenburg spreadsheet uses the Manning equation for discharge given the bankfull elevation, local channel geometry, slope, and Manning’s roughness coefficient. The Manning’s roughness coefficient “n,” was approximated using the results of the Wolman pebble count to account for bed material roughness, as well other factors that influence channel roughness observed in the field. Using the method described in the USGS Guide for Selecting Manning's Roughness Coefficients for Natural Channels and Floodplains (Arcement, Jr, and Schneider, 1984), this included adjustments for channel irregularity, variation in cross section, effects of obstruction, vegetation, and channel geometry. This calculated roughness coefficient value was entered into the Mecklenburg spreadsheet to provide a more accurate prediction of the channel roughness. These datasets are included in Appendix A. Table 4 summarizes information from these measurements. Conditions unique to each reach are outlined further below.

Table 4: Geomorphic Data and Stability Summary

Water Bankfull Reach Bankfull Bank Width Entrench- Valley Stream Field Surface Cross- Sinu- Reach Length Discharge Height Depth ment Slope Type XS # Slope sectional osity (ft) (cfs) Ratio Ratio Ratio (ft/ft) (ft/ft) Area (ft2) 1 C6 484 1 .013 3.1 3.9 1.5 83.7 4.1 1.08 0.006 2a G6 323 2a 0.014 2.7 6.6 4.5 9.3 1.9 1.19 0.009 2b E6 372 2b 0.014 3.3 8.1 3.3 10.3 4.0 1.04 0.005 3 G6 1363 3 0.004 5.4 8.9 6.1 9.5 1.2 1.11 0.003

4 F6 576 4 0.005 7.6 11.8 3.9 18.5 1.2 1.01 0.001

5 G6 1373 5 0.009 4.4 9.2 6.6 10.2 1.5 1.23 0.003

6 E5 1,162 6 0.006 6.8 16.0 1.8 10.2 4.2 1.20 0.005

7 F5 235 7 0.011 5.9 16.7 3.5 13.5 1.1 1.00 0.005

8 F5 763 8 0.003 7.1 16.7 4.5 9.6 1.2 1.12 0.002

9 E5 550 9 0.004 12.3 19.6 1.2 8.6 17.0 1.14 0.004

10 C4 1050 10 0.009 9.5 23.0 1.6 13.0 2.4 1.31 0.002

Bankfull regional regressions relationships between dimensions of bankfull channel geometry (i.e., width, mean depth, cross-sectional area) and water discharge or drainage area are useful in stream assessment to validate field identified bankfull elevations and in the development of preliminary design concepts. The applicability of the derived predictive equations is limited to rivers similar to those providing the data. Thus, empirical relationships for channel geometry are applicable only for rivers in specific hydro-physiographic regions with relatively homogeneous climate, geology, and vegetation (McCandless 2003). Using approximate drainage areas determined from Streamstats (2012) at various locations along the project, two bankfull regional regressions were used to estimate bankfull geometry; the USGS Bankfull Regional Curves for Streams in the Non-Urban, Non-Tidal Coastal Plain Physiographic Province (Krstolic, J.L., and Chaplin, J.J., 2007) and the USFWS Maryland stream survey: Bankfull discharge and channel characteristics of streams in the Coastal Plain hydrologic region (McCandless 2003). These results are summarized in Table 5.

Table 5: Bankfull Regional Regression Results

Colony Crossing Central Elem School DA Limit 0.17 sq mi 0.241 sq mi Associated Reaches 1 to 4 5 to 10 Regional Curve USGS USFWS USGS USFWS BF Cross Sectional Area 3.87 2.99 4.82 3.81 Bankfull Width 5.47 5.25 6.20 5.99 Mean BF Depth 0.71 0.57 0.78 0.64 Bankfull Discharge 9.81 8.60 12.05 11.06

Although strong field indicators within the Study Area were not present in most locations due to severe channel incision and lack of inner berms or depositional features, the field measured bankfull dimensions and discharge estimates corresponded reasonably well with the regional regression results.

5.2.2.1 Reach 1 (Antiqua Place to beginning of minor headcut formations)

Overview Reach Description This reach is located on private property and originates at a storm drain outfall. It is characterized by a stream/wetland complex with a defined, vertically and laterally stable baseflow channel with low bank heights and complex floodplain microtopography. Stream banks in this reach are the most stable observed during field reconnaissance and was not studied as part of the geomorphic assessment. This reach may be utilized during the design phase as a possible reference reach.

Key observations:  The channel and floodplain are well connected. Overbank flows are frequent. Floodplain microtopography is complex and includes numerous depressions.  This reach is fully contained within a delineated wetland.

 Instream habitats are homogenous, with a mostly featureless bed and little diversity in habitat type or water depth.  The channel begins to slightly incise at the downstream limit of the reach becoming less connected to its floodplain, ending at a small knickpoint.

5.2.2.2 Reach 2 (Beginning of minor headcut formations to major headcut formations)

Overview Reach Description This reach is located on private property and originates at a small headcut. The upper reach, characterized by cross section 2A, is a sand bed stream with pool/run features that has begun to incise. Run features are comprised of sporadic woody debris or exposed roots. The floodplain width is constrained in the middle of the reach by South River Colony Water Quality Pond #7, resulting in significant channel confinement. Below this point on the lower portion of the reach, characterized by cross section 2B, the available floodplain width expands and the stream channel becomes less incised with lower bank heights but remains incised. The stream bed in this location is also pool/run dominated, with significant backwater caused by a debris blockage at the time of assessment.

Key observations:  In the upper portion of this reach, the stream valley is significantly confined by the encroachment of the South River Colony Water Quality Pond #7 embankment, which negatively impacts channel stability by limiting available floodplain width.  Water Quality Pond #7 pond embankment appears to have been partially breached. Suggest County inspected riser for possible blockage and repair gully in embankment.  This reach is adjacent to two delineated wetlands located in a drainage path from the golf course and the right floodplain  A portion of the channel flows subsurface under exposed tree roots just above the Water Quality Pond #7 outfall.  An 18 inch HDPE outfall collecting runoff from the golf course enters this reach along a relatively stable outfall channel protected with rip rap.  Downstream of the pond outfall, this reach runs along the left valley toe of slope. Based on this planform location, the channel may have been horizontally relocated to the edges of the stream valley due to past land use practices.  The wooded riparian area along the left bank is narrow and at a higher elevation than the right bank floodplain, with maintained lawn extending near the tops of stream banks along the golf course.  The downstream end of the reach is located just upstream of the series of significant knickpoints developed from a large headcut migrating upstream. Because the channel has no natural grade control to impede its progress, the headcut will likely continue to migrate through this reach.

5.2.2.3 Reach 3 (Major headcut formations to upper limit of in-line pond backwater influence)

Overview Reach Description This reach is located on Anne Arundel County property and originates at a series of knickpoints. The last of which is a severe headcut approximately 5 feet high above a large scour pool. The reach is a sand and silt/clay bed stream with pool/run features. The reach is characterized by alternating vertical cut banks on each outer bend and small depositional point bars on the inner bends. The reach is severely downcut to the underlying clay and over-widened, with flows that are completely disconnected from the floodplain.

Key observations:  Near the upper end of the reach in the vicinity of the main channel headcut, a severe headcut several feet high is located within a side stormwater conveyance channel, likely a result of main channel incision. This channel continues towards the residential development and ends within the forested area. County GIS data indicate that storm drain outfall P25O008 is located in this vicinity, but the South River Colony Parcel D Storm Drain plans indicate this pipe is routed to Water Quality Pond #5. There was no evidence of the outfall during the field assessment.  This reach is adjacent to several small delineated wetlands located on the left overbank floodplain.  The upper portion of this reach runs along the left valley toe of slope as in reach 2, before shifting to the right valley toe for the majority of the reach. Based on this planform location, the channel may have been horizontally relocated to the edges of the stream valley due to past land use practices. Channel ditching at the roadway crossings is also a possibility that may have initiated channel incision due to base level changes at these locations.  Water Quality Pond #5 off Hunt Club has experienced significant damage to the outfall protection and the downstream side of the embankment due to the stream channel instabilities in this area.  A CMP outfall from the large golf course pond in front of the clubhouse periodically receives flows from irrigation system and periodically discharges to the stream valley. The pond is a reservoir for the golf course irrigation system, the pond is recharged with groundwater pumping. Visual observations indicate a large volume of flow with high velocities is generated during these discharge events, causing a large headcut formation downstream of outfall within the channel from the outfall to the stream. Stabilization of this outfall channel should be addressed by the stream restoration design.  Outfall P240021 contains 2 pipes from the storm drain and Water Quality Pond #1 coming to one headwall. The outfall protection has been scoured out and pushed rip rap into stream channel, leaving the headwall structure undermined.  The wooded riparian area along the right bank is narrow where several properties off of Hunt Club Court push against the channel.  The downstream end of the reach is located above what appears to be the upper limit of the in-line stormwater management pond (South River Colony Parcel D SWM Basin D-1) backwater influence.

5.2.2.4 Reach 4 (Upper limit of in-line pond backwater influence to Colony Crossing)

Overview Reach Description This reach is located on Anne Arundel County property and originates at the upper limit of backwater influence from the in-line stormwater pond. The reach is a straightened, incised and over-widened channel with silt/clay bed stream with little bed form diversity. The reach is characterized by frequent debris blockages and depositional material throughout the bed due to the influence of the in-line SWM pond. The reach is disconnected from the floodplain at its upper limits but transitions to lower bank heights and better floodplain connection at its downstream end where excessive deposition in the channel has resulted in the blockage of the pond 12 inch low flow pipe. The floodplain consists of a densely forested wetlands with a canopy consisting mainly of tulip poplar, beech, and oak.

Key observations:  This reach is partially contained within a delineated wetland within the existing in-line stormwater basin.  This reach runs along the right valley toe of slope as in the downstream section of reach 3. Based on this planform location, the channel may have been horizontally relocated to the edges of the stream valley due to past land use practices. Channel ditching at the roadway crossings is also a possibility that may have initiated channel incision due to base level changes at these locations.  The wooded riparian area along the right bank contains a more densely vegetated understory than other sections of riparian area, with an overstory that includes beech trees along the stream valley sideslope. This is located at a higher elevation than the left bank, which is a forested floodplain with little understory.  The downstream end of the reach is the in-line SWM pond (South River Colony Parcel D SWM Basin D-1) located just upstream of Colony Crossing. The pond is providing some level of flow attenuation to the downstream reaches. Per the as-built drawings, SWM Basin D1 appears to have been designed to provide 2- and 10- year control based on the configuration of the riser. The 2-year WSEL is set at the riser opening and is controlled by the 12 inch low flow. The 10-year WSEL is likely partially controlled by the riser opening. It does not appear that the pond provides any control for the 100-year event.  The 12 inch low flow pipe is currently blocked by sediment trapped within the stream channel leading to it, with no visual evidence of the low flow structure except for the top of the headwall and a small amount of flow pushing through the blockage. The pond basin appears to have deposited a significant amount of sediment generated from the upstream channel erosion, and has likely lost a significant portion of the storage volume.  Per the as-builts, because the 12 inch low flow pipe was set at the channel bottom, it provides no permanent pool water quality volume. And because of the large size of the low flow pipe diameter, it likely provides little attenuation of the flow rate during frequent storm events. Because there is no separate emergency spillway, the 100-yr flow is routed though Colony Crossing via the 54 inch principle spillway pipe, and discharges onto rip rap outfall protection

5.2.2.5 Reach 5 (Colony Crossing to road crossing connecting Central Elementary School to South River High School

Overview Reach Description This reach is located on Anne Arundel County property and originates at the downstream end of the Colony Crossing culvert. The reach is a silt/clay bed stream with pool/run features. The reach is characterized by alternating vertical cut banks on each outer bend and small depositional point bars on the inner bends along an irregular meander pattern. The reach is severely downcut to the underlying clay and overwidened, with flows that are completely disconnected from the floodplain.

Key observations:  At the upper end of the reach, the Colony Crossing culvert outfall and South River Colony Water Quality Pond #2 outfalls are both stabilized with rip rap protection down to the sewer crossing. Just below the sewer crossing is an approximate 3 feet high headcut that immediately drops into the incised stream channel.  Approximately 140 feet below the top of the reach, a 325 feet long side channel beginning from overland flow from the golf course and outfall P24O025 has developed into a severely incised gully, likely due to the main channel incision.  This reach is adjacent to two small delineated wetlands located on the left floodplain at the upstream end, and the right floodplain at the downstream end.  The downstream end of the reach is the road crossing by South River High School. The double barrel culvert is partially blocked with sediment and woody debris causing an accumulation of loose sediment deposits upstream of the culvert.

5.2.2.6 Reach 6 (Central Special School Access Road to approx. 300 feet upstream of MD 214)

Overview Reach Description Reach 6 originates at two 54 inch CMP culverts which convey flow under an access road to Central Special School. Downstream of the outfall, bank heights were found to be approximately 3 feet high with evidence of active bank erosion in the outside of the meander bends that has exposed tree roots. Continuing downstream bank heights become lower (1.5- 2 feet) and the channel appears to have some access to its floodplain during storm events. The channel is relatively straight with low sinuosity. Mid way through the reach a dirt access road crosses over Glebe Branch via two 44 inch by 72 inch elliptical RCP culverts. Immediately downstream of the elliptical RCP culvert, riprap has been placed in the channel and appears to be stable. The reach is mostly void of riffle and pool features with bed material composed mostly of sand and silt.

Key observations:

 Overland flow originating at an 18 inch RCP located southwest of Central Elementary school enters the mainstem approximately 75 feet downstream of the twin 54 inch CMP culverts.

 Riprap in the channel, located approximately 400 feet downstream of the twin 54 inch CMP culverts, is temporarily holding grade and preventing a headcut from migrating upstream.

 Several relic channels and active overflow channels within the floodplain were noted during the field assessment.

 A 24 inch RCP, possibly draining the Central Elementary School grounds, is located on the left floodplain, immediately upstream of the dirt access road. Minor erosion to the outfall channel was noted before turning to overland flow as flow continues to Glebe Branch.

 Downstream of the dirt access road, a 30 inch CMP (P24O007) outfalls onto the right floodplain where overland flow continues to the mainstem.

5.2.2.7 Reach 7 (Approx. 300 feet upstream of MD 214 to the MD 214 culvert)

Overview Reach Description This reach begins approximately 300 feet upstream of MD 214 and continues to a 66 inch by 33 inch elliptical culvert that conveys flow beneath MD 214. This reach is characterized by an increase in bank height (5-6 feet) and the presence of multiple headcuts throughout. The channel through this reach is currently incising, likely due to a change in the downstream culvert invert and/or ditching during the crossing installation. This lowering of the base level control has exposed many tree roots which are currently holding grade preventing the upstream migration of headcuts.

Key observations:

 The adjacent abandoned floodplain/terrace was likely wetland prior to channel incision. It now consists of upland forest due to the lack of hydrology.

5.2.2.8 Reach 8 (MD 214 to backwatered channel)

Overview Reach Description Reach 8 begins downstream of the 66 inch by 33 inch elliptical culvert under MD 214 and continues for approximately 763 feet until the channel is stabilized with gabion baskets. This reach is severely entrenched and over widened with 6 to 8 foot raw, vertical banks. The channel through this reach has low sinuosity with the exception of the downstream limits of the reach where there are multiple heavily eroded bends.

Key Observations:

 Gabions are holding grade at the downstream end of Reach 8 and preventing a headcut from migrating upstream.

5.2.2.9 Reach 9 (Start of backwatered channel to Mayo Road)

Overview Reach Description This reach begins approximately 550 feet upstream of Mayo Road and is characterized by lower bank heights and floodplain connectivity in the upper portion of the reach as a result of backwater from the two 27 inch CMP culverts under Mayo Road. Continuing downstream, the channel slope steepens as a result of several headcuts working up through the system. Bank heights exceed 4 or 5 feet at the downstream end of the headcuts.

Much of the adjacent floodplain is forested wetlands with a large quantitative SWM Pond constructed along the left floodplain. The SWM pond outlets via two 8 foot by 5 foot box culverts to an outlet channel which conveys flow approximately 400 feet to its confluence with the main stem just upstream of the Mayo Road crossing. The channel appears to be deviating from the center of the valley, as evidenced by floodplain elevations, and is currently confined against the roadway embankment.

Key Observations:

 The upstream portion of Reach 9 has floodplain connectivity and is currently backwatered by the Mayo Road culverts.

 Several headcuts are working up through the lower extents of the reach, causing the channel to steepen and bank heights to increase.

 The channel has been ditched within the floodplain that is 2 to 3 feet higher than the lowest floodplain elevations. The stream is not located within the lowest portion of the valley. The tributary from the large storm water management facility is located within a large wetland in the lowest elevation within the floodplain just upstream of Mayo Road. This explains the high bank heights. The higher flows do not follow the channel but flow down valley toward the large wetland area to the north. This reduces the rate of bed degradation as the flow within the channel is limited to smaller frequency events.

5.2.2.10 Reach 10 (Mayo Road to the tidal influence of Glebe Creek)

Overview Reach Description This reach originates at two 27 inch culverts downstream of Mayo Road and continues to the point of tidal influence. The majority of the reach is confined by the residential neighborhood of Shore Drive and the valley wall. Bank heights were found to be 1 to 2 feet with multiple small headcuts in the upstream portion of the reach and upland forest or maintained lawn on the floodplain. Continuing downstream, the valley widens and the floodplain becomes forested wetland.

5.3 Stream Stability Evaluation 5.3.1 Causes, Nature and Extent of Instability The Glebe Branch watershed and the surrounding area has undergone a series of changes typical of developed Anne Arundel County. Prior to colonial settlement, the stream was likely a stable periodically wet valley bottom that did not have a defined single thread channel. Base level or profile controls that would have prevented head cuts and gully formation would have included conditions representing some or all of the following: fallen woody material scattered across the valley bottom, extremely shallow low stress flood flows, and extensive herbaceous vegetation with rooting depths and densities capable of preventing any incision or channelization within the valley bottom. Following rural colonial settlement, the area was deforested and transitioned to agricultural land use that transitioned back to forest several decades ago. A second deforestation followed during the urbanized residential development with and without the installation of adequate stormwater management devices. The historic land use changes and current urbanized conditions are causing predictable impacts to the stream network within the watershed and the project Study Area.

Possibly the most significant modern driver of further channel degradation within the Study Area is likely caused by the impacts of the roadway crossings. When installed, it is likely the stream channel approaches to the culvert crossings were lowered to facilitate setting the culvert inverts several feet below the floodplain elevation. The following excerpt from the Washington Department of Fish and Wildlife, Water Crossings Design Guidelines (Barnard et al., 2013), accurately describes the likely process of the head cut initiation and migration, and the associated channel incision that has occurred at Glebe Branch due to these roadway crossings construction.

A channel degrades when its bed scours and lowers over time either by natural process, hydrologic changes in the watershed and/or the lowering or removal of a control point in the channel.

Channel headcut occurs when the upstream channel has been lowered locally by scour in response to a replacement culvert that has been enlarged and/or set at a lower elevation. The headcut itself is a steep section of channel that, as it erodes, migrates upstream and eventually lowers the entire channel for some distance. The same situation occurs if an undersized culvert is replaced with a larger one, since the flood hydraulic profile is lowered by the reduction of the culvert constriction. Habitat impacts of channel degradation can be extensive but short-lived as the channel adjusts to the new elevation. In cases where the impacts are unacceptable and prolonged, they can be managed by reconstruction of the upstream channel either into a natural grade or steepened with hydraulic controls.

A reach degrades when there is a net lowering of the bed elevation. During the initial stages of degradation, a channel will become deeper and narrower, the relative height of the banks increases and the banks steepen. Loss of floodplain connection and concentration of flows within the channel exacerbate the degrading process. Reinforcement of root structure is decreased. As a result of erosion, banks fail, and the channel then widens over a period of time until the channel reestablishes its natural slope, floodplain, bankfull width and depth at the lower elevation. This process is shown graphically in Figure 7.3.

A few important details are shown in Figure 7.3. Incision is confirmed by a progressive increase in the distance between the top of bank and the thalweg of the channel. What was once a floodplain (stage I) becomes a terrace which is never again inundated (stage III). The primary nickpoint in this figure has progressed to the road crossing where it is stopped by the non-erodible steel or concrete culvert. This primary nickpoint is often, although not always, followed by a secondary nickpoint or several smaller ones. In the design of a crossing the engineer must be aware that this secondary nickpoint may be approaching the crossing within the lifespan of the proposed structure. The profile must be long enough to recognize this feature and the planned culvert set deep enough to accommodate its passage. (Barnard et al, 2013)

The sediment load being delivered to the stream channel along the Study Area is minimal due to the storm flows within the contributing drainage areas being conveyed via storm drain pipe and several water quality ponds. The developed drainage areas consisting of residential development and golf course are not producing excessive sediment.

Channel aggradation is occurring locally upstream of each roadway crossing due to the backwater and the excessive streambank erosion generated sediment load being delivered along with woody debris. This is most evident and severe within the in-line SWM pond located above Colony Crossing.

5.3.2 Stream Evolution Model Sequence

Using the Stream Evolution Model (SEM) developed by Cluer and Thorne (Cluer and Thorne, 2014), the current stage of the channel is Stage 4, Degradation and Widening. See Figure 3 below.

Figure 3: Stream Evolution Model (SEM)

The goal of the restoration approaches described below in section 6 will be to reverse the evolution of the channel and re-establish a stable end point within Stage 0 and 1 depending on the reach.

The physical and vegetative attributes table for each stage in the Stream Evolution Model is described in Table II of their document. The habitat and ecosystem benefits for each stage are characterized in Table III of their document. Both tables are included for reference in Appendix H.

The descriptions in Section 6 Preliminary Conceptual Design provide the specific approaches necessary for the targeted end point for each restoration reach given the site conditions.

5.4 Bank Stability Analysis and Erosion Estimate A bank stability analysis was conducted to determine the potential quantity of bank erosion within the Study Area. The Bank Assessment for Non-Point Source Consequences of Sediment (BANCS) model (Rosgen, 2001, 2006) was conducted using the Bank Erosion Hazard Index (BEHI), and Near-Bank Stress (NBS) evaluations. Site mapping in Appendix I includes the limits of erosion rate predictions based on the BEHI and NBS evaluations. This appendices also contains a table summarizing the results of the evaluations and the predicted erosion rates. The rates are based on the North Carolina regional curve that estimates sediment loading. The North Carolina regional curve was chosen over the USFWS curve for Hickey Run in

Washington, DC due to discrepancies in the methodology used at Hickey Run to collect the BEHI and NBS data compared to the development of the curve.

Glebe Branch is a system that is heavily influenced by storm water flows. These come from both the adjacent neighborhoods and the South River Golf Course. Over time,several headcuts have developed throughout the reaches. These headcuts are moving upstream due to continued high flow events and are actively transporting sediment downstream. A minimal amount of the transported sediment is stored within channel banks as benches, but a significant amount is likely stored in depositional areas upstream of culverts and within the in-line stormwater basin at Colony Crossing.

The inventory followed the Bank Assessment for Non-Point Source Consequences of Sediment (BANCS; Rosgen, 2006). The BANCS method estimates the rate of erosion and the volume of bank material delivered to the stream via bank erosion. It is a field-based visual assessment tool that, when combined with empirical studies, can be used to predict estimates of erosion rates.

The BANCS method integrates two erodibility tools to estimate erosion rates: 1) The Bank Erosion Hazard Index (BEHI), and 2) Near Bank Stress (NBS). The BEHI is a bank erodibility estimation tool that assesses streambank erosion condition and potential. To develop the BEHI rating at a location, the following physical parameters are assessed: 1) study bank height, 2) bankfull height, 3) root depth, 4) root density, 5) bank angle, and 6) surface protection. Field- measured variables are converted to a risk ratings between 1 and 10 with corresponding adjectives values of risk (e.g., very low to extreme). A BEHI measurement is typically performed prior to construction, with the implicit assumption that post-construction sediment loss will be negligible. (In a situation where this assumption is not appropriate, then the BEHI method can also be applied after construction.) The second assessment is Near Bank Stress (NBS). NBS variables are used to adjust the BEHI prediction based on the potential disproportionate energy distribution in the near-bank portion of the channel cross section. Along the Project Limits, NBS was assessed using the Level 1 rapid assessment diagram from the WARSSS protocol (Rosgen, 2006).

There are a number of empirical curves that have been developed for the prediction of bank erosion using the BEHI/NBS methodology. The most regionally similar method for Glebe Branch is the North Carolina curve (NCSU SRP, 1989) Table 6 summarizes erosion rates predicted using North Carolina methodology. Collectively, the curves suggest an erosion rate of 547 tons per year. When normalized by unit length of bank, the predicted erosion rate along the Glebe Branch project Study Area is 0.066 tons/year/foot. These findings suggest that a significant amount of sediment can be prevented by the proposed restoration approach.

Table 6 Summary of BEHI predictions

Predicted erosion rate Predicted erosion rate per unit project length Empirical Curve (CY/yr) (Tons/yr) (Tons/yr/ft) North Carolina 420.8 547.1 0.066

In order to compare predicted erosion rates from the regional curves with actual field measurements, bank pins were installed at several typical cross sections (see geomorphic map for cross section locations). At cross section 2B and 3, pins were installed on the right bank. At cross section 5, pins were installed on the left bank. As large storm events occur during the design phase, the exposure of these pins will be monitored.

One shortcoming of the BANCS prediction is the potential rapid degradation of somewhat stable reaches located above a rapidly migrating headcut. In BANCS, these reaches do not predict high levels of potential erosion because of the stable channel condition. However, as the headcut migrates upstream into these reaches, a large volume of sediment can be lost. Predicting this potential may be possible by estimating the potential sediment wedge above each headcut using channel survey and determine the rate of headcut migration.

6 PRELIMINARY CONCEPTUAL DESIGN

6.1 Restoration Approach Alternatives Analysis Based on the information collected and assessed, the JV identified preliminary restoration approaches appropriate for the project Study Area. These approaches provided the initial starting point for design development. Two design approaches have been developed to compare impacts to existing natural resources, discuss the design approaches success at meeting the project goals, and additional benefits and concerns with each approach. Below is a description of both approaches. Both approaches are similar to a Rosgen Priority 1 approach of replacing the incised channel with a new, stable stream at existing floodplain elevation to result in a stream and wetland complex with the most potential for long-term stability. This approach was considered appropriate at this site because of the considerable width of existing stream valley available without significant constraint.

Alternative 1: Floodplain restoration/baseflow channel design with complete channel realignment. This approach includes significant adjustments to the channel cross section, profile, and planform. The channel cross section will be sized to convey baseflows within much smaller channel dimensions, both width and depth, than the existing channel dimensions. Preliminary sizing is based on an approximate design flow of half the predicted bankfull discharge results from the regional regression analysis. By sizing the channel to convey only base flow, this will result in frequent out of bank flows onto the broad forested floodplain. The existing channel will be filled near the top of bank elevation, with some areas remaining low as depressional floodplain features. Channel stability will be based on use of grade control structures along the active channel flowpath to maintain the targeted bed elevation just below the floodplain elevation. The materials to construct these grade controls will be determined based on hydraulic model results. The planform will be realigned to the center of the stream valley. This relocation away from the steep valley slopes reduces potential bank erosion and provides greater for more belt width and sinuosity. Valley wide grade control and surface habitat will be applied as needed. Woody material cut on site will be recycled within the channel and valley.

Alternative 2: Floodplain restoration/baseflow channel design with minor channel realignment. This approach includes significant adjustments to the channel cross section and profile, with

© Biohabitats, Inc 31 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW minor planform adjustments primarily within the existing channel top of bank. The channel cross section will be sized to convey baseflows as described in Alternative 1, with the channel invert set just below the targeted floodplain elevation to reconnect frequent storm flows to the floodplain. The existing channel will be filled just below the proposed top of bank elevation, based on the proposed channel depth, with proposed structures built mostly within this fill. Channel stability will be based on reducing flow depth and shear stress via reconnection of frequent storm flows to the full floodplain width, and the use of grade control structures along the active channel flowpath to maintain the targeted bed elevation. The materials to construct these grade controls will be determined based on hydraulic model results using a combination of rock and wood material. The location and frequency of valley wide grade control will also be assessed with the hydraulic model results. Valley wide grade control and surface habitat will be applied as needed. Woody material cut on site will be reused within the channel and valley for habitat and roughness features. The planform will remain primarily within the existing channel top of bank to utilize the open corridor the over-widened existing channel has provided. This will minimize impacts to the riparian forest and wetlands. Where necessary, minor alignment changes may be necessary to provide more a stable planform in specific locations. In addition, there are potential outfalls and outfall channels that could be identified to stabilize and enhance. This would improve the ecological function and would be included in both approaches. Riparian enhancements will be established in conjunction with both the proposed approaches and would depend on the extent and elevation of grading operations associated with the restoration approaches. To convey the proposed approaches for each reach, a plan view and typical section schematic of each approach was developed. All design features shown are preliminary schematic level based on GIS base mapping and field assessment work. The grade lines shown are intended to be approximate valley grading based on the GIS LIDAR data to determine slope and approximate floodplain tie in locations, and are not intended to represent the actual site grading plan. Based on the significant elevation difference of the adjacent private properties and the stream valley bottom, hydraulic trespass (the increase of 100 year water surface elevation) on private property as a result of floodplain reconnection is not anticipated. However, further design analysis and modeling will be required to confirm this along the Study Area limits.

6.2 Restoration Techniques A variety of geomorphic and engineering techniques will be used, in conjunction with professional judgment and experience to create a long-term, stable channel design that restores functional attributes for Glebe Branch. The following techniques were evaluated for incorporation into the design to ensure channel stability, create and maintain aquatic and terrestrial habitat features and enhance the riparian forest structure:

1. Floodplain reconnection. Reconnecting the channel to the floodplain to deliver frequent flows to these vegetated systems capitalizes on natural floodplain functions critical to ecosystem health, including sediment trapping; material processing; reduction in downstream flooding; increases in concentration time of floodwaters; and reduction in volumes through infiltration, evaporative losses, and depressional storage. Furthermore,

channel overflow contributes to groundwater recharge and maintenance of summer low flows, providing support for wetland and vernal pool hydrology and ecology, suppression of non-native invasive plant species, and increased micro-habitat diversity.

2. Channel realignment. Channel realignment (and associated reconfiguration) will involve modifying the cross-sectional and planform geometry to provide a more stable and complex morphology. In some areas, realignment of the channel allows a shift away from steep banks and facilitates reconnection to the floodplain.

3. In-channel structures. To provide grade control at the proposed bed elevations, deflect flow, and enhance aquatic habitat, in-channel structures will be installed along the proposed channel. These may include and integrate woody debris, log and rock materials. Future channel incision will be prevented by adding these structures using boulders to maintain the bed elevation as designed. The expected benefits would include establishing a stable channel invert, mitigating head cuts and maintaining instream habitat features upstream and downstream of the structures. Steep transition reaches to connect an elevated stream channel to roadway crossing elevations may require cascades or step pool systems.

4. Wetland creation & enhancement. Wetland enhancement and creation may alternate between localized areas of floodplain excavation for the establishment of depressional features, elevating the stream channel for more frequent flooding of the adjacent floodplain areas and elevating the stream valley groundwater table, or larger scale removal of deposition adjacent to the stream channel to reconnect the stream and the floodplain. Wetland expansion or reestablishment of historic wetlands integrated with the stream will have the positive impact of water quality improvement associated with increased stormwater retention time and improved denitrification. Other benefits include the conversion of the stream valley bottom vegetation to a more wet adapted community that supports wetland ecological functions and the suppression of non-native invasive species. This conversion may result in some long-term die off of upland trees within the stream valley bottom that is acceptable to the County. The trade-off of some long-term die off of existing upland trees within the stream valley bottom with a robust wetland community is acceptable to the County.

Where incoming flows from stormwater outfalls can be redirected into open areas, wetlands can be used to enhance infiltration and provide ecological benefits. Most of the outfall tie in locations will flow directly into a restoration floodplain wetland if the stream channel instabilities are addressed. In few cases, additional measures may be necessary due to elevation difference between the outfalls and the valley bottom to hold water surfaces at different elevations and create a diversity of broad pools and wet areas that detain and treat stormwater before entering stream valley bottom. Techniques may consist of a combination of sand berms, shallow aquatic pools and cobble riffles The expected benefits would include storm water quality and quantity control over a range of storm flows, enhanced habitat, and enhanced aesthetic appeal. Seasonal depressional wetlands, or vernal pools, are one type of wetland that can be incorporated in the design through grading techniques. For example, where meander bends are abandoned due to channel realignment, depressions can be left along the previous alignment to support plant and animals species dependent on this increasingly rare habitat.

5. Riparian enhancement. Riparian enhancement will include augmenting the existing vegetation communities by introducing native canopy and understory species, and controlling invasive species.

6. Invasive species control. During field assessment Multiflora rose (Rosa multiflora) and Japanese Stiltgrass (Microstegium vimineum) were both found in the project area. Active control includes initial and ongoing treatment of invasive species to ensure the health of the evolving riparian forested community and associate ecosystem function. In areas invaded by invasive species, the upper soils (e.g., top 2 ft) will not be salvaged from areas proposed for grading to prevent recolonization of invasive species post-construction. Passive control can be achieved via the suppression of non-native invasive species through development of a hydrologic regime outside of their normal tolerance range. Converting the floodplain to a wetter condition, will suppress much of the invasive species with the site limits.

7. Bank Grading/Protection. We do not anticipate using significant lengths of bank regrading to adjust the bank angle to more stable, gradual slopes within the existing planform and profile. However, this may be necessary in short transition reaches in and out of existing roadway crossings. At locations where regrading banks to a gradual, stable slope is not possible, bank protection measures will be needed. This may take the form of rock bank revetments. These methods are suitable for addressing full bank erosion along steep banks (>2:1 slope) where site constraints dictate. Using this method it is planned that the site will be a balanced site, the excavated soil from the bottom of the project site may be used as channel fill throughout the upper section of the site.

6.3 Approaches by Reach The following section outlines the preliminary restoration approaches that were identified by reach. For each reach, construction access and the associated limit of disturbance will require additional field review and consideration during later phases of the design. Additionally, the location of utilities will need to be evaluated in conjunction with any specific practices.

Reach 1 (Antiqua Place to beginning of minor headcut formations) Alternative 1: Do Nothing Alternative 2: Install grade control within downstream limits of reach

Overview This portion of the project Study Area is fully contained within a jurisdictional wetland, and contains a well-connected, stable stream channel. There is an opportunity to install grade control structure(s) at the downstream end to prevent active head cuts that threatens the upstream wetland complex. However, such work would involve disturbance to the existing wetland that would have to be weighed.

Specific actions:  Evaluate need for grade control at downstream end of reach to ensure headcut does not migrate upstream and degrade existing wetland. Evaluation requires results of the hydraulic analysis results.  Evaluate condition of existing wetland vegetation and propose planting enhancements

Ongoing considerations:

 Preserving stability of reach without negatively impacting wetland

Reach 2 (Beginning of minor headcut formations to major headcut formations) Alternative 1: Floodplain restoration/baseflow channel design with complete channel realignment and conversion of water quality pond to integrated stream/wetland complex.

Overview In the upper section of this reach, we are proposing raising the existing stream channel to just below the forested floodplain wetland elevation located upstream. A new channel will be re-align through the existing water quality pond to improve planform geometry and open up the active floodplain that is currently constricted by the pond footprint and embankment. The new channel will be sized to convey base flow with low shear stress within the channel and floodplain. Furnished bed material may be required within the new channel at critical locations for grade control. The existing channel will be plugged and filled in key locations while other location will be converted to floodplain depressions or side channels. The proposed valley slope within this reach is approximately 2.1% based on approximate valley grading shown on the concept plan, the steepness of which may require additional protection measures. The proposed stream relocation will continue downstream into reach 3.

Specific actions:  Select planform alignment that centers stream and minimize disturbance to trees and wetlands, as reasonable.  Breach Water Quality pond #7 and convert pond footprint to stormwater wetland integrated with stream  Reconnect proposed channel to existing floodplain where feasible. Furnished streambed material may be necessary, pending hydraulic modeling results  Strategically install valley grade controls and large woody surface material  Fill existing channel and maximize floodplain depressional areas along former channel  Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy  Determine need for replacing water quality pond functions

Alternative 2: Floodplain restoration/baseflow channel design within existing channel alignment.

Overview This approach proposes the same baseflow channel design at just below the floodplain elevation, but within the existing channel alignment. This eliminates the removal of the water quality pond, creating the possible need for a more armored channel around the channel within this constricted reach. The pond outfall protection will need to be addresses within the stream design. Below the pond, the channel remains within the alignment, but has frequent access to the expansive floodplain on the right bank. Because the proposed channel will be narrower

© Biohabitats, Inc 35 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW than the existing channel top width, the alignment can be shifted slightly away from the left toe of slope while still minimizing impacts to the right bank riparian floodplain. The proposed valley slope within this reach is approximately 2.1% based on approximate valley grading shown on the concept plan, the steepness of which may require additional protection measures. The proposed stream relocation will continue downstream into reach 3.

Specific actions:  Incorporate Water Quality Pond #7 outfall protection into stream design  Reconnect proposed channel to existing floodplain where feasible. Furnished streambed material may be necessary, pending hydraulic modeling results  Strategically install valley grade controls and large woody surface material  Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy

Reach 3 (Major headcut formations to upper limit of in-line pond backwater influence) Alternative 1: Floodplain restoration/baseflow channel design with complete channel realignment.

Overview Within this reach, the baseflow channel relocated to the center of the stream valley continues, along with the plugged and filled existing stream channel. In the upper section of this reach, there are more opportunities for significant depressional areas and secondary flow paths because of the available floodplain width. The channel will be relocated away from the water quality pond embankment, with the pond outfall flowing directly into a floodplain depression created from the abandoned channel at this location. The proposed valley slope is approximately 1.0% based on approximate valley grading shown on the concept plan. The proposed stream relocation will continue downstream into reach 4.

Specific actions:  Select planform alignment that centers stream and minimize disturbance to trees and wetlands, as reasonable.  Repair the downstream side of the Water Quality Pond #5 embankment  Reconnect proposed channel to existing floodplain where feasible  Strategically install valley grade controls and large woody surface material  Fill existing channel and maximize floodplain depressional areas along former channel  Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat  Provide grade control within outfall channel below the private 30” outfall from the golf course pond

 Daylight both outfalls in the vicinity of Water Quality Pond #1 to the valley toe of slope

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy

Alternative 2: Floodplain restoration/baseflow channel design within existing channel alignment.

Overview This approach continues the same baseflow channel design at just below the floodplain elevation, but within the existing channel alignment with some minor realignment where advantageous, such as at the water quality pond outfall location. Below the pond, the channel remains generally within the alignment, but has frequent access to the expansive floodplain on the left bank. Because the proposed channel will be narrower than the existing channel top width, the alignment can be shifted slightly away from the right toe of slope while still minimizing impacts to the right bank riparian floodplain. The proposed valley slope is approximately 1.0% based on approximate valley grading shown on the concept plan. The proposed stream channel will continue downstream into reach 4.

Specific actions:  Repair the downstream side of the Water Quality Pond #5 embankment  Reconnect proposed channel to existing floodplain where feasible  Strategically install valley grade controls and large woody surface material  Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat  Provide grade control within outfall channel below the private 30” outfall from the golf course pond  Daylight both outfalls in the vicinity of Water Quality Pond #1 to the valley toe of slope

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy

Reach 4 (Upper limit of in-line pond backwater influence to Colony Crossing) Alternative 1: Floodplain restoration/baseflow channel design with complete channel realignment and conversion of in-line stormwater basin to stormwater wetland.

Overview Within this upper portion of this reach, the baseflow channel relocated to the center of the stream valley continues, along with the plugged and filled existing stream channel. The channel will be relocated away from the right bank stream valley wall, creating opportunities for floodplain depression along the reach in the abandoned channel. The proposed valley slope is approximately 0.9% based on approximate valley grading shown on the concept plan.

At the downstream end of this reach, the proposed baseflow channel is routed around the existing in-line stormwater management basin (SWM Basin D-1) to the left edge of the valley,

© Biohabitats, Inc 37 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW ending at a proposed stormwater wetland. Baseflow from the stream would be routed directly into the principle spillway of the riser, with the existing low flow orifice abandoned. A proposed berm separates the baseflow channel from the existing stream channel, which would be converted to an offline section of the stormwater wetland. This alternative would significantly modify the storage of stormflows currently being provided by the in-line basin. However, without significant modification to the riser, a stormwater wetland could provide improved water quality treatment for the drainage. Detailed modeling of the existing and proposed condition will be necessary to determine the feasibility of this alternative.

Specific actions:  Select planform alignment that centers stream and minimize disturbance to trees and wetlands, as reasonable.  Reconnect proposed channel to existing floodplain where feasible  Strategically install valley grade controls and large woody surface material  Fill existing channel and maximize floodplain depressional areas along former channel  Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat  Daylight stormdrain outfall P24O021 and Water Quality Pond #1 outfall structures to toe of slope  Convert existing in-line stormwater basin to a stormwater wetland

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy  Determine the allowable impacts to the downstream reaches associated with significantly modifying the performance of the existing in-line stormwater basin.

Alternative 2: Floodplain restoration/baseflow channel design within existing channel alignment and re-establishment of in-line stormwater basin.

Overview This approach continues the same baseflow channel design at just below the floodplain elevation, but within the existing channel alignment with some minor realignment where advantageous. The channel remains generally within the alignment, but has frequent access to the expansive floodplain on the left bank. Because the proposed channel will be narrower than the existing channel top width, the alignment can be shifted slightly away from the right toe of slope while still minimizing impacts to the right bank riparian floodplain. The proposed valley slope through this reach is approximately 1.2% based on approximate valley grading shown on the concept plan.

Near the downstream end of this reach, the proposed baseflow channel transitions from the floodplain elevation to the existing streambed via a cascade drop structure to tie into the in-line basin elevations. The location of this structure will need to be determined based on the amount of desired storage to remain in the existing in-line basin. Between the proposed cascade and the existing low flow orifice, the existing channel will need to be excavated to remove the

© Biohabitats, Inc 38 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW excessive sediment deposition through the basin storage area. This option provides for returning the in-line basin to some level of its original storage capacity.

Specific actions:  Reconnect proposed channel to existing floodplain where feasible  Strategically install valley grade controls and large woody surface material  Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat  Daylight stormdrain and pond outfall structures to the toe of slope  Return the storage capacity of the existing in-line stormwater basin to some level of the original design.

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy  Determine the desired storage capacity necessary to be maintain in the existing in-line stormwater basin

Reach 5 (Colony Crossing to road crossing connecting Central Elementary School to South River High School) Approach 1: Floodplain restoration/baseflow channel design with complete channel realignment.

Overview Within this reach, the baseflow channel relocated to the center of the stream valley begins immediately below the stable rip rap outfall protection at the Colony Crossing culvert. Because of the elevation of the floodplain at this location, the proposed channel may be set at a slightly higher elevation (approximately 47 feet) than the downstream invert of the Colony Crossing culvert based on as built information. However, the resulting backwater is not expected to extend past the upstream culvert invert. These elevations will need to be confirmed with field survey, and may result in the need to lower the proposed channel elevation slightly.

In the upper section of this reach, there are more opportunities for significant depressional areas and secondary flow paths because of the available floodplain width. The proposed valley slope through this reach is approximately 1.1% based on approximate valley grading shown on the concept plan. The proposed stream relocation continues downstream to just above the Central Elementary Access Road culvert, where the stream must transition quickly within the backwater area from the floodplain elevation to the existing culvert invert.

 Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat  Stabilize nearly 300 feet of channel below outfall P24O025 using an SPSC

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy  Determine proposed channel elevation downstream of Colony Crossing culvert that does not negatively impact culvert capacity.

Alternative 2: Floodplain restoration/baseflow channel design within existing channel alignment.

Overview This approach continues the same baseflow channel design at just below the floodplain elevation, but within the existing channel alignment with some minor realignment where advantageous. The channel remains generally within the alignment, but has frequent access to the expansive floodplain on the left bank. Because the proposed channel will be narrower than the existing channel top width, the alignment can be shifted slightly away from the right toe of slope while still minimizing impacts to the left bank riparian floodplain. The proposed valley slope through this reach is approximately 1.1% based on approximate valley grading shown on the concept plan. The proposed channel continues downstream to just above the Central Elementary Access Road culvert, where the stream must transition quickly within the backwater area from the floodplain elevation to the existing culvert invert.

Specific actions:  Reconnect proposed channel to existing floodplain where feasible  Strategically install valley grade controls and large woody surface material  Scatter wood for flow roughness and habitat improvements  Install woody debris in stream to enhance existing aquatic habitat  Stabilize nearly 300 feet of channel below outfall P24O025 using an SPSC

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy

Reach 6 and 7 (Central Elementary Access Road to MD 214)

It should be noted that the abandoned roadway and embankment can be removed for both Alternatives 1 and 2.

Alternative 1: Floodplain restoration/baseflow channel design with complete channel realignment.

Overview

In the uppermost 100 feet we are proposing lowering of the floodplain to tie into the Central Elementary Access Road culvert. A new channel re-alignment capable of conveying base flow conditions on the existing floodplain is proposed. The location will be located, flagged and surveyed in the field to reduce the impacts to the forest and trees. Furnished bed material will be provided for a certain width within the new channel. The existing channel will be blocked in key locations while other locations will be converted to vernal pools or side channels. A floodplain depression is proposed at the storm drain outfall northeast of the culvert.

We are proposing the removal of the pedestrian or access road and embankment and a replacement of a longer span pedestrian bridge if necessary. The proposed stream relocation will continue downstream to MD 214 crossing. A new valley or floodplain is proposed beginning approximately 250 feet upstream of MD 214 to mitigate for the numerous headcuts within the reach. The proposed valley slope is approximately 2.2% based on approximate valley grading shown on the concept plan. The concept indicates that the transition occurs outside of SHA ROW.

Specific actions:  Minimize disturbance to trees and wetlands, as reasonable.  Attach proposed channel to existing floodplain where feasible  Install stormwater treatment pool  Strategically install valley grade controls and large woody surface material  Remove abandoned roadway embankment

Ongoing Considerations:  Preserving existing tree canopy  Transition into MD 214

Approach 2: Floodplain restoration/baseflow channel design with minor channel realignment.

Overview In the uppermost 100 feet we are proposing lowering of the floodplain to tie into the Central Elementary Access Road culvert. Short reaches of new relocated channel are proposed to add sinuosity and reduce the potential for bed degradation. This will require raising the existing channel invert to less than 6 inches below the existing floodplain. The proposed additional stream length will be flagged and surveyed in the field to minimize tree impacts. Furnished bed material will be provided at key locations for a certain width within the new channel or existing channel. The existing channel will be blocked in key locations while other locations will be converted to vernal pools or side channels. A stormwater treatment facility is proposed at the storm drain outfall northeast of the culvert.

We are proposing that the abandoned access road remain as it provides significant backwater and grade control to the upstream reach. Due to the backwater created by the culvert and embankment, vertical grade control can be minimized.

Downstream of the abandoned road, a new channel relocation to MD 214 is proposed similar to Alternate 1. However, a shorter and steeper transition is proposed upstream of the MD 214 crossing to reduce tree impacts. The proposed slope immediately upstream of MD 214 is approximately 3.3% based on approximate valley grading shown on the concept plan. The concept indicates that the transition occurs within SHA ROW.

Ongoing Considerations:  Preserving existing tree canopy  Transition into MD 214

Reach 8 and 9 (MD 214 to Mayo Road)

Alternative 1: Floodplain restoration/baseflow channel design with complete channel realignment.

Overview The uppermost 100 feet will include a pre-formed scour pool and lowering of the floodplain to tie into the MD 214 culvert system. A new channel re-alignment capable of conveying base flow conditions on the existing floodplain is proposed. The location will be located, flagged and surveyed in the field to reduce the impacts to the forest and trees. Furnished bed material will be provided for a certain width within the new channel for the majority of the proposed reach. Due to the backwater condition created by the Mayo Road culvert, imported bed material may not be required at the downstream extent. The existing channel will be blocked in key locations while other locations will be converted to vernal pools or side channels. The proposed channel will be relocated to the lowest part of the valley immediately upstream of Mayo Road and confluence with the tributary flowing from the large storm water management pond. This will also mitigate for the numerous headcuts within the existing reach upstream of Mayo Road.

Specific actions:  Minimize disturbance to trees and wetlands, as reasonable.  Attach proposed channel to existing floodplain and wetlands where feasible  Strategically install valley grade controls and large woody surface material  Relocate channel to lowest point of the valley along the approach to Mayo Road. Confluence with and follow the pond out fall channel to the Mayo Road crossing.

Ongoing Considerations:

 Minimizing wetland impacts and preserving existing tree canopy

Approach 2: Floodplain restoration/baseflow channel design with complete channel realignment except for transition to Mayo Road.

Overview The uppermost 100 feet will include a pre-formed scour pool and lowering of the floodplain to tie into the MD 214 culvert system. A new channel re-alignment capable of conveying base flow conditions on the existing floodplain is proposed. The location will be located, flagged and surveyed in the field to reduce the impacts to the forest and trees. Furnished bed material will be provided for a certain width within the new channel for the majority of the proposed reach. Larger bed material will be required where the slope increases near Mayo Road as remediation for the existing headcuts. The existing channel will be blocked in key locations while other locations will be converted to vernal pools or side channels.

Specific actions:  Minimize disturbance to trees and wetlands, as reasonable.  Attach proposed channel to existing floodplain and wetlands where feasible  Strategically install valley grade controls and large woody surface material  The proposed channel alignment will approach the Mayo Road crossing along the existing channel alignment.

Ongoing Considerations:  Minimizing wetland impacts and preserving existing tree canopy

6.4 Roadway Culvert Analysis Century Engineering, Inc. was asked to evaluate the feasibility of culvert replacement options for three culvert crossings as part of the Glebe Branch (also known as Glebe Creek) Stream Restoration Project in Anne Arundel County, Maryland. The stream restoration project includes the restoration of approximately 8,500 linear feet of degraded channel by channel realignment and stabilizing the proposed channel at the existing floodplain elevation. Raising the three culverts within the project limits to the existing floodplain elevation will retain floodplain connection throughout the project area. Below is a summary of each culvert replacement option. This analysis should be considered cursory and preliminary at this stage.

Colony Crossing Culvert

An in-line stormwater management pond is located on the upstream end of the existing culvert with a 12-inch diameter low-flow pipe mostly blocked with sediment at an invert of 47.5 (from Concept Design plans). Based on GIS contours, the estimated downstream culvert invert is 46.0 and the top of roadway elevation is approximately 66.0. The discharge of the 100-year rainfall event at this crossing is estimated to be 322 CFS (StreamStats Version 3.0, included in Appendix J).

To connect the floodplains on both the downstream and upstream end of the culvert, the culvert will need to be raised to an elevation of approximately 54.0 on the upstream end. It is conservatively assumed the proposed culvert will require four feet of cover from the top of

© Biohabitats, Inc 43 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW roadway to top of culvert. To achieve the desired inverts, adequate cover, and to pass the 100- year rainfall event with at least one foot of freeboard to the top of roadway, a 12’-0” x 3’-0” (inside dimensions) concrete box culvert will be required. Tailwater data is based on the provided Concept Plans. The slope of the proposed culvert is assumed to be 1.03%. See HY-8 included in Appendix J.

The proposed concrete box culvert is the most feasible culvert replacement option due to the large flow area required to safely pass the 100-year rainfall event and limited amount of vertical distance from the proposed inverts to the top of roadway. Replacing the existing culvert with a bridge would be significantly more expensive. The estimated cost to replace the existing culvert with a 12’-0” x 3’-0” concrete box culvert is $490,000 - $590,000. See cost estimate included in Appendix J.

Unnamed Road at School

Twin 54-inch CMP culverts convey Glebe Branch from southwest to northeast under an unnamed road to Central Elementary School and Central Special School. The existing upstream invert of the culvert is 32.0 (from Concept Design plans) and the estimated top of roadway elevation is approximately 47.0 based on GIS contours. The discharge of the 100-year rainfall event at this crossing is estimated to be 475 CFS (StreamStats Version 3.0, included in Appendix J).

To connect the floodplains on both the downstream and upstream end of the culvert, the culvert will need to be raised to an elevation of approximately 32.0 on the upstream end. It is conservatively assumed the proposed culvert will require four feet of cover from the top of roadway to top of culvert. To achieve the desired inverts, adequate cover, and to pass the 100- year rainfall event with at least one foot of freeboard to the top of roadway, one 48” round concrete culvert and two 54” round concrete pipe culverts could be proposed. Tailwater data is based on the Concept Plans. The slope of the proposed culvert is assumed to be 1.00%. See HY-8 included in Appendix J.

Replacing the existing twin 54” CMP culvert with a triple round concrete culvert (1-48” pipe and 2-54” pipes) is a relatively inexpensive option to connect the floodplains on each side of the roadway while safely conveying the 100-year rainfall event. The estimated cost to replace the existing culvert is $340,000 - $415,000. See cost estimate included in Appendix J.

Central Avenue (MD 214)

One 66” x 33” CMP culvert conveys Glebe Branch from southwest to northeast under Central Avenue (MD 214). The upstream invert of the culvert is estimated to be approximately 18.0 based on GIS contours and the top of roadway elevation is estimated to be approximately 23.0. The discharge of the 100-year rainfall event at this crossing is estimated to be 805 CFS (StreamStats Version 3.0, included in Appendix J).

To connect the floodplains on both the downstream and upstream end of the culvert, the culvert will need to be raised to an elevation of approximately 21.0 on the upstream end. With limited cover over the existing culvert (estimated to be 3.0’ maximum) it is not possible to raise the culvert and safely convey the 100-year rainfall event. The existing CMP culvert could be replaced with a bridge to connect the floodplains and safely pass the 100-year rainfall event.

The estimated cost to replace the existing culvert with a bridge is $2,340,000 - $2,860,000. See cost estimate included in Appendix J.

6.5 Stormwater Management Basin D1 Analysis SWM Basin D1 from the South River Colony Parcel D SWM As-built plans appears to have been designed to provide 2, 10, and 100- year control based on the available as-built and limited design report information. In order to confirm the level of control the pond is providing, and assess the impact of potential changes made to the riser configuration, we have developed a preliminary model based on best available information.

As-Built Design Conditions The design flows used to model storage within the pond are based on StreamStats regression data and as-built pond information for the Southern River Colony Parcel D Storm Water Management project. Both the drainage area contributing to and the storage within SWM Basin D1 are modelled with HydroCAD Stormwater Modeling software. Basin Characteristics data computed by StreamStats, including percent of impervious area, percent of type A and C/D hydrologic soil types, and percent of forested area within the drainage basin, serve as the basis for estimation of land use and soil components for the contributing drainage area. These values were visually verified with available GIS data. The contributing drainage area used in the model is 124 acres, obtained from the as-built pond data sheets. The time of concentration path is based on available GIS data and applicable StreamStats Basin Characteristics data. Flow rates for the 2-year, 10-year, and 100-year storms entering the pond from the contributing drainage area are found below in Table 8.

Table 8: Pond Inflow Rates for 2-year, 10-year, and 100-year Storms

Storm Inflow Rate Frequency (cfs) 2-year 75.91 10-year 195.81 100-year 353.76

Contours are digitized from provided pond as-builts. This digitized contour information, along with as-built data for the 12-inch low-flow outlet pipe, riser, and 60-inch RCP culvert for SWM Basin D1, are used to model stage storage within the pond. The HydroCAD model is calibrated to the water surface elevations provided in the as-builts for the 2-year, 10-year, and 100-year storms. The modelled flow rates for the 2-year, 10-year, and 100-year storms, as well as the resulting water surface elevations, for this scenario are shown in Table 9 below.

Existing Conditions – Blocked Low Flow In the existing conditions model, the contributing drainage area remains the same and the pond is modified to reflect current existing conditions. Since installation, the pond has filled in with sediment up to an elevation of approximately 50.9 feet, the elevation at which the top of the headwall for the 12-inch low-flow outlet pipe is located. In this model, the bottom of the basin is set at 50.9 feet and the 12-inch low-flow pipe is removed. Attenuated flow rates for the 2-year, 10-year, and 100-year storms for this scenario are shown in Table 9 below.

Proposed No Riser – Existing Spillway Pipe In the no riser model, the contributing drainage area remains the same but it is assumed that the riser will be removed from SWM Basin D1 and the pond will directly outfall to the existing 60-

© Biohabitats, Inc 45 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW inch RCP culvert. In this model, the bottom of the basin is set at the as-built invert for the 60- inch RCP culvert, 47.19 feet. Attenuated flow rates for the 2-year, 10-year, and 100-year storms for this scenario are shown in Table 9 below.

Proposed No Riser - Raised Box Culvert In the raised culvert- no riser model, the contributing drainage area remains the same and it is assumed that the riser will be removed from SWM Basin D1 and the pond will directly outfall to a proposed 12 foot x 3 foot concrete box culvert. In this model, it is also assumed that the outlet pipe will be raised to an upstream invert elevation of 54 feet. The slope of the box culvert will be kept at as-built conditions, setting the downstream invert elevation at 52.25 feet. The bottom of the basin is set at 54 feet. Attenuated flow rates for the 2-year, 10-year, and 100-year storms for this scenario are shown in Table 9 below.

Table 9: Pond Outflow Rates for 2-year, 10-year, and 100-year Storms

2-Year Storm 10-Year Storm 100-Year Storm Scenario Outflow Peak Elev Outflow Peak Elev Outflow Peak Elev (cfs) (ft) (cfs) (ft) (cfs) (ft) As-Built 11.85 57.31 80.06 59.58 179.91 61.48 Design Conditions Existing 13.21 58.06 83.97 59.95 186.60 61.83 Conditions – Blocked Low Flow No Riser – Ex 75.04 56.47 182.09 53.4 259.89 57.25 Spillway Pipe No Riser – 68.74 55.47 175.12 56.74 286.51 58.30 Raised Box Culvert

Storm Water Management Control Conclusion The preliminary model confirmed the existing SWM Basin is providing nearly the same level of control under existing conditions as the as-built condition for the 2, 10, and 100-year events. Under the two proposed scenarios, nearly all of the peak flow control is lost for the 2 and 10 year event. A small amount of peak flow control is predicated for the 100 year event. This result will need to be taken into consideration when determining the preferred restoration approach at this location, and the downstream reaches, especially considering the undersized culvert located at the Mayo Road crossing.

Water Quality Control The required Water Quality Volume of the contributing drainage area is approximately 121,757 cubic feet, based on 124 acres with approximately 24.5% impervious. Based on site assessment observations, it appears that the existing SWM basin provides little if any water quality control. The 12 inch low flow pipe is buried below the channel bottom, thus providing no permanent pool water quality storage. Because of the size of the low flow orifice (12 inches), it likely provides little attenuation of the flow rate during frequent storm events.

Based on the as built plans and limited design report information, the basin appears to have been graded to provide a small amount of permanent pool storage. This volume was approximated to be 9588 cubic feet using the as built contour information, which equates to

© Biohabitats, Inc 46 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW approximately 8% of the required water quality volume. To obtain this credit, the pond would need to be excavated to reestablish the original storage of the pond.

6.6 Functional Assessment and Ecological Uplift Evaluation The Final Draft Function-Based Rapid Stream Assessment Methodology (Starr et al 2015) was applied to this project to understand and illustrate likely functional improvements of the two proposed alternatives over the existing conditions. The assessment was broken up by reach, with each reach having an existing conditions and proposed alternative analysis table evaluated under the framework headings of Hydrology, Hydraulics, Geomorphology, Physicochemical, and Biology. The analysis tables are included in Appendix L.

Hydrology Hydrology functions transport water from the watershed to the channel. This project will have limited impact on the delivery of water to the channel, as the watershed is mostly piped via storm drain systems. However, some potential opportunities exist at outfalls along the project to remove the direct connection to the stream channel (such as daylighting outfall P240021 back to the toe of the stream valley and an SPSC at the receiving stream of outfall P24O025). However, whole-scale changes of concentrated flow delivery to the stream are not possible with this project.

Hydraulics Hydraulic functions transport water in the channel, on the floodplain and through sediment (Harman et al, 2012 and Fischenich, 2006). This level of the pyramid is directly related to floodplain connectivity. Improved connectivity result in runoff volumes slowed and stored throughout the wide, vegetated floodplain and not within the stream channel alone which results in channel adjustment and incision due to headcut processes. Both proposed alternatives have the potential for significant improvements to this level because they are based on baseflow channel design and floodplain reconnection.

Geomorphology Geomorphology is the transport and storage of wood and sediment to create diverse bed forms and dynamic equilibrium (Harman et al, 2012 and Fischenich, 2006). This level is primarily driven by 3 parameter; riparian vegetation, lateral stability, and bedform diversity.

Overall, this site has high potential for improvement from non-functioning to functioning because of the available vegetated floodplain. Both alternatives provide high potential for improvements to lateral stability and bedform diversity because of the baseflow channel design approach. However, Alternative 2 does not provide the potential for improving on a lacking riparian width in some locations because it remains in the existing channel alignment.

Physiochemical Physiochemical functions include the interaction of physical and chemical processes to create the basic water quality of the stream, as well as to facilitate nutrient and organic carbon processes (Harmen et al, 2012 and Fischenich, 2006). Because one goal of the restoration approach is to enhance and reestablish a wetland floodplain integrated with the stream channel, denitrification of impaired stormwater entering the site is anticipated.

Although the stormwater entering the Study Area appeared to be relatively clear based on visual observations, there is likely high levels of nutrients coming into the system from the golf course

© Biohabitats, Inc 47 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW and maintained yards of the surrounding residential development. Also, the site itself is a large contributing source of sediment and nutrient into the stream system as a result of accelerated bank and bed erosion. The potential for increased function of this level is preventing sediment from entering system during storm flow, processing instream and riparian nutrient during baseflow conditions through improved hyporeic zone exchange, and reconnecting the floodplain to the stream channel to maximize denitrification through integrated floodplain wetlands. These three goals are provided nutrient removal credit as described in Recommendations of the Expert Panel to Define Removal Rates for Individual Stream Restoration Projects (Schueler & Stack, January 2014).

Another method to improve this level of the pyramid is to increase wood into the stream channel and promote conditions that will collect and store leaf material. This will improve material processing along the flowpath

Biological Biology functions include processes that support the life histories of aquatic and riparian plants and animals (Harmen et al, 2012 and Fischenich, 2006). The ability of the lotic system to support biological processes is dependent upon the hydrology, hydraulics, geomorphology, and physiochemical functions as described previously. Recent biological monitoring data must be analyzed to determine existing communities of macroinvertebrates and fish within the existing stream. Following construction of the restoration, post-construction monitoring is advisable to determine the biological uplift achieved with the project. With increased function of the lower levels of the functional pyramid, it is anticipated that scores could increase. However, these communities are highly sensitive to a range of influences that likely will not be monitored as part of the success criteria with this project.

6.7 Water Quality Credits 6.7.1 Chesapeake Bay TMDL Waste Load Reduction Ongoing and recent research demonstrates differences in nutrient and sediment delivery rates between healthy, degraded and restored urban streams. In particular, urban streams experience high rates of channel erosion that deliver large volume of sediment to the channel network. The stream restoration community has taken recent action to better quantify the benefits provided by constructed stream restoration projects that reduce nutrient and sediment loads. In 2010, an expert panel reviewed available science on the nutrient and sediment removal performance associated with qualifying urban stream restoration projects in relation to those generated by degraded urban stream channels. Since that time, various groups have reviewed and “test driven” the recommendations to refine them. The revised and approved recommendations were released in January 2014, and provide a procedure to quantify estimates of removal rates in smaller zero- to third-order stream reaches not simulated in the Chesapeake Bay Watershed Model (Schueler & Stack, January 2014).

Table 10 summarizes the predicted annual load reductions in total nitrogen, total phosphorus, and total suspended solids using the standard revised, approved credit rates for stream restoration for both alternatives. These values can be used for planning purposes to estimate the potential water quality benefits of the proposed stream restoration project.

Table 10: Removal Rate Predictions

TN TP TSS*

Revised Interim Reduction Rate 0.075 0.068 43.4 (lb/ft/yr) Predicted Annual Load Reduction for restoration of 504 457 291,431 6,715 LF (lb/yr) *rate for Non-Coastal Plain, includes representative edge-of-field rates and is subject to a sediment delivery ratio.

The Expert Panel Report includes a method for predicting removal rates in a more detailed fashion that potentially can be used to demonstrate even greater reductions in TN, TP, and TSS. The four protocols are listed below, but have not been calculated for this report.

 Protocol 1: Credit for Prevented Sediment during Storm Flow  Protocol 2: Credit for Instream and Riparian Nutrient Processing during Base Flow  Protocol 3: Credit for Floodplain Reconnection Volume  Protocol 4: Credit for Dry Channel RSC as an Upland Stormwater Retrofit.

The baseflow channel, floodplain restoration approach will likely achieve credits for Protocol 1, 2 and 3.

6.7.2 MDE NPDES Impervious Area Treatment

The MS4 permit involves restoration of twenty percent of a jurisdiction’s impervious surface area that has little or no stormwater management. The impervious area restoration requirement is part of the strategy in Maryland’s Watershed Implementation Plan (WIP) for meeting the Chesapeake Bay TMDL (MDE 2014). Impervious area treatment credits is 1 acre for every 100 linear feet of stream restoration projects. Based on a length of 6,715 linear feet for the full length of recommended restoration (reaches 2 through 9), the project could qualify for 67 impervious acre credits. MDE will also allow outfall stabilization to take credit toward impervious area restoration according to the same credit of 1 acre per 100 linear feet of the project.

6.8 Recommendations Based on the analysis presented, Alternative 1 – Baseflow channel design with complete channel re-alignment, is recommended for the majority of all reaches to meet the project goals and objectives stated in Section 1.2 using the approach and techniques described in Section 6 to maximum ecological uplift. However, additional site information will be obtained within the Schematic Design phase that requires some modification to this approach. Cost considerations have not been factored into this recommendation.

6.9 Future Design Development Following the review and approval of this report, the JV and the County will select a preferred design approach and project limits to move forward into Schematic Design that includes a

© Biohabitats, Inc 49 Glebe Branch Stream Restoration Watershed and Site Assessment Report Anne Arundel County DPW preliminary 30% design. Prior to beginning Schematic Design, several items to be further clarified:  Determine limit of topographic survey sufficient to cover the selected work areas  Determine geotechnical investigation locations.  Determine necessary assessment/field evaluation worked necessary for schematic design and future permitting (Rosgen Level III assessment or similar)  Identify locations and needs for 2D modeling  Determine what level of analysis is required for modeling impacts of in-line pond and water quality pond modifications (if selected as preferred approach)  Clarify the County’s preferred method of documenting pollutant load reduction credits  Determine public outreach timing and scope  Obtain recent Anne Arundel County stream restoration bid tabulations or open end unit costs to use as basis for engineer’s estimate of probable construction cost.

7 REFERENCES AND CORRESPONDENCE

7.1 References Barnard, R. J., J. Johnson, P. Brooks, K. M. Bates, B. Heiner, J. P. Klavas, D.C. Ponder, P.D. Smith, and P. D. Powers (2013), Water Crossings Design Guidelines, Washington Department of Fish and Wildlife, Olympia, Washington. http://wdfw.wa.gov/hab/ahg/culverts.htm

Cluer, B. and Thorne, C. (2014), A STREAM EVOLUTION MODEL INTEGRATING HABITAT AND ECOSYSTEM BENEFITS. River Res. Applic., 30: 135–154. doi: 10.1002/rra.2631

Fischenich JC. 2006. Functional Objectives for Stream Restoration. Vicksburg, MS: US Army Engineer Research and Development Center. EMRRP Technical Notes Collection ERDC TN- EMRRP-SR-52.

G.J Arcement, Jr, and V.R.Schneider, 1984. Guide for Selecting Manning's Roughness Coefficient For Natural Channels and Flood Plains. United States Geological Survey Water- supply Paper 2339.

Harman, W., R. Starr, M. Carter, K. Tweedy, M. Clemmons, K. Suggs, C. Miller, 2012. A Function-Based Framework for Stream Assessments and Restoration Projects, May.

Harman, W. and R. Starr. 2011. Natural Channel Design Review Checklist. US Fish and Wildlife Service, Chesapeake Bay Field Office, Annapolis, MD and US Environmental Protection Agency, Office of Wetlands, Oceans, and Watersheds, Wetlands Division. Washington, D.C. EPA 843-B-12-005.

Krstolic, J.L., and Chaplin, J.J., 2007, Bankfull regional curves for streams in the non-urban, non-tidal Coastal Plain Physiographic Province, Virginia and Maryland: U.S. Geological Survey Scientific Investigations Report 2007–5162, 48 p. (available online at http://pubs.water.usgs.gov/sir2007–5162.

Maryland Department of Environment (MDE). 2014. Accounting for Stormwater Wasteload Allocations and Impervious Acres Treated. Baltimore Maryland. Pp. 53. http://www.mde.state.md.us/programs/Water/StormwaterManagementProgram/Documents/NP DES%20MS4%20Guidance%20August%2018%202014.pdf

Maryland Geologic Survey, 2008. Physiographic Map of Maryland. Available online at http://www.mgs.md.gov/geology/physiographic_map.html. Accessed 6/8/2016

Maryland State Archives. Maryland Manual On-Line, "Maryland at a Glance," March 16, 2016. http://msa.maryland.gov/msa/mdmanual/01glance/html/mdglance.html. Accessed 8/16/2016

McCandless, T. L. (2003). Maryland stream survey: Bankfull discharge and channel characteristics of streams in the Coastal Plain hydrologic region. US Fish and Wildlife Service, Chesapeake Bay Field Office, CBFO-S03-02.

Mecklenburg 2006. The Reference Reach Spreadsheet for Channel Survey Data Management. Ohio Department of Natural Resources.

North Carolina State University Stream Restoration Program, 1989. North Carolina Piedmont Region Bank Erosion Prediction Curve. Available online at http://www.bae.ncsu.edu/programs/extension/wpg/srp/. Accessed 6/8/2016

Rosgen, D.L. (2006b). Watershed Assessment of River Stability and Sediment Supply (WARSSS). Fort Collins, CO: Wildland Hydrology.

Rosgen, D. 2001. A practical method of computing streambank erosion rate. Proceedings of the Seventh Federal Interagency Sedimentation Conference. Vol. 2, pp. 9-15. March 25-29, 2001, Reno, NV.

Rosgen, D.L. 2016. River Morphology and Applications Class Handout. Wildland Hydrology Books, Fort Collins, CO.

Rosgen, D.L. and H.L. Silvey. 1996. Applied River Morphology. Wildland Hydrology Books, Fort Collins, CO.

Schueler, T. & B. Stack, 2014. Recommendations of the expert panel to define removal rates for individual stream restoration projects. Prepared by the Chesapeake Stormwater Network & the Center for Watershed Protection, January 17.

Schumm, S.A., M.D. Harvey, and C.A. Watson. 1984. Incised channels: morphology, dynamics and control. Littleton, CO: Water Resources Publications.

Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. Accessed [February 2016].

Starr, R., Harman, W., and Davis, S. 2015. Final Draft Function Based Rapid Stream Assessment Methodology. Habitat Restoration Division, Chesapeake Bay Field Office, U.S. Fish and Wildlife Service. CAFÉ-S15-06.

Starr, R.R., McCandless, T.L., Eng, C.K., Davis, S.L., Secrist, M.A., and Victoria, C.J. (2010). Western Coastal Plain Reference Reach Survey. U.S. Fish and Wildlife Service, Chesapeake Bay Field Office, CBFO-S10-02.

U.S. Geological Survey, 2012, The StreamStats program for Maryland, online at http://water.usgs.gov/osw/streamstats/maryland.html.

U.S. Fish & Wildlife, 2014. BEHI erosion rate curves, Excel file provided by Rich Starr, November.

U.S. Geologic Survey. 2012. Maryland geologic map data. Available online at http://mrdata.usgs.gov/geology/state/state.php?state=MD. Accessed 6/8/2016.

U.S. Geological Survey. Gunpowder quadrangle, Maryland [map]. 1:62,500. Grid Zone “A”. Chief of Engineers, U.S. Army, 1941.

U.S. Geological Survey. White Marsh quadrangle, Maryland [map]. 1:24,000. 7.5 Minute Series. Army Map Service, Edited and published by the Geological Survey, 1949.

Wolman, M.G., 1954. A method of sampling coarse river-bed material. Transactions of American Geophysical Union, 35: 951-956.

APPENDIX A: EXISTING CONDITIONS AND DRAINAGE AREA MAP, GEOMORPHIC ASSESSMENT DATA AND SOILS REPORT

APPENDIX B: HISTORICAL IMAGERY AND MAPPING

APPENDIX C: NATURAL RESOURCE INVENTORY REPORT

APPENDIX D: AGENCY CORRESPONDENCE LETTERS

APPENDIX E: AS BUILT DRAWINGS

APPENDIX F: REFERENCE REACH SEARCH

APPENDIX G: PHOTOGRAPHIC LOG

APPENDIX H: SEM MODEL TABLES

APPENDIX I: BANCS RESULTS

APPENDIX J: ROADWAY CULVERT ANALYSIS

APPENDIX K: SWM BASIN D1 ANALYSIS

APPENDIX L: FUNCTIONAL ASSESSMENT TABLES