Stephen J. Souza, Ph.D. Princeton Hydro, LLC

Transcription

1 Stephen J. Souza, Ph.D. Princeton Hydro, LLC

2 Project Overview Project Team Princeton Hydro, LLC Simone & Collins, LA Aquetong Creek a first & second order stream - Ingham Spring through former bed of Aquetong Lake to dam breach. Route 202 tributary Intermittent, stormwater driven stream. Develop restoration/management plan for streams and adjacent floodplain/riparian areas.

3 Project Goals Restore the re-emerging stream channel by engineering the characteristics of a stable, natural system, including minimizing sediment loading of the stream. Return stream to a historic cold water creek system while simultaneously improving the ecological integrity of the surrounding riparian habitat.

4 To Meet Project Goals Stabilize stream channel and exposed lake bottom. Control/eliminate invasive plant species. Enhance/create cold-water species supporting habitat. Improve ecological functions of riparian and upland areas. Create sustainable park setting emphasizing passive recreation.

5 Legacy Sediment Limited amount of unstable sediment deposition within the former lake bottom. However some downcutting of Aquetong Creek. Downcutting geomorphological term describing active erosion of sediment from stream channel. Defined by stream s hydrologic and hydraulic attributes, topography and sediment properties. Severity of channel instability and riparian erosion thus far minimal.

6 Hydrology Creek s hydrology fairly stable. Contributing watershed relatively small. Ingham Spring s average flow is 2,000 GPM = approximately 2.9 MGD. Supplemental inflow - Stormwater from the southern developed area. Intermittent stream from the northern developed area mitigated by detention basin and pond. Not a hydraulically flashy system.

7 Drainage area = 239 acres

8 Existing Vegetation Comprehensive biotic assessment conducted in November Walked entire site, detailed assessment of multiple quadrats located along five transects. Predominant vegetation identified and boundaries of major biotic groups and invasive species mapped. Data used to... Identify areas requiring intensive invasive species management. Guide future enhancement planting efforts.

9 Vegetation Transects

10 Vegetation Three wetland communities in former lake bottom Emergent herbaceous wetland borders Aquetong Creek... broadleaf cattail (Typha latifolia) and soft rush (Juncus effusus); woolgrass (Scirpus cyperinus), skunk cabbage (Symplocarpus foetidus), and narrowleaf cattail (Typha angustifolia). Wet meadow proximate to Aquetong Creek dominated by monoculture of curly dock (Rumex crispus) and dense black willow (Salix nigra). Distal wet meadow dominated by rough barnyard grass (Echinochloa muricata) and eastern cottonwood (Populus deltoides) saplings. Three major stands of Phragmites

11 Wetlands

12 Invasive Species Existing Vegetation

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14 Stream Biota Basic investigation of benthic macroinvertebrate community. Stream substrate qualitatively examined. Random locations sampled using D-net and large stones overturned. Ephemeroptera, Plecoptera, and Tricoptera colonizing stream...indicative of high quality stream. Also Tipulidae (crane flies), amphipods, isopods, mollusks (Corbicula), and Planaria (flatworms). Corbicula non-native, invasive clam, was likely in lake.

15 Fluvial Geomorphometry Geomorphic analysis quantifies depth and distribution of legacy sediments and assesses existing channel stability. Use data to identify stream reaches subject to ongoing geomorphic adjustment and instability. Develop management recommendations for impacted reaches. Compared to downstream reference reach which provided an estimate for equilibrium channel cross-sectional dimensions for the upstream reach.

16 Stream Geometry Majority of sediment in lower stream reach, first evidence of downcutting approximately 100 ft upstream of the former dam. Lower/central reach incised and entrenched, characterized by ft of erodible sediment. Upper reach has less erodible sediment, ave depth 0.7 ft. Due to fairly constant inflow and minimal sediment loading. Finer sediment mostly in lower reaches of stream. But only need to remove ~ 6,000 yds 3.

17 Site Stability To date extent of downcutting minimal. Why? Consistent baseflow and limited flood flows. Relatively small watershed. Moderate amount of sediment accumulation within stream channel. Controlled breach of dam and excellent sediment management. Township re-seeding and planting efforts. Quick colonization by pioneer species.

18 Overview Highlight X-Section Remove sediment, widen channel, expand floodplain Remove sediment, widen channel, expand floodplain Limit of channel modification

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20 Trail System

21 Recommendations Maximize passive recreational use of site. Acknowledge site history. Create opportunities to bring people into restored riparian area and close to stream. Extensive trail system consisting of both ADA compliant and mulched walking paths. Create multiple stream crossings. Create public activity areas...picnic, living classroom, bird watching...etc. Bike path along northern boundary of site.

22 Recommendations Aggressively manage invasive species; Phragmites, reed canary grass, knotweed, multiflora rose...may require repeated cut/treat approach. Continue tree and meadow planting efforts...will help stabilize area, add shade to stream channel, and control annual invasives (e.g., stilt grass). Focus tree planting within upland and more stable riparian areas (e.g., southeastern corner). Careful with tree planting along stream edge.

23 Recommendations - Lower Main Stem Aquetong Creek Selective excavation of channel...target unconsolidated sediment prone to erosion and downstream transport. Channel expansion to stable width. Create floodplain bench adjacent to expanded channel...allows spread of flood flows across wider area of developing riparian area.

24 Recommendations - Main Stem Aquetong Creek Approximately 770 ft of the channel targeted for restoration. Replicate stable channel that exists below breach. Design to 14.5 ft wide and 1 ft deep. Excavate floodplain bench two times the channel width, with a stable 3H:1V slope to meet the surrounding grade.

25 Recommendations - Rte 202 Tributary Most of effort on central and lower reach of tributary...approximately 450 ft. Channel width 7 ft and depth 0.6 ft Floodplain bench 14 ft wide. Stabilization at mouth of Rte 202 culvert. May also involve importation of large rock and raising of stream bed to increase frequency of out of bank flows. Aggressive replanting of riparian area.

26 Recommendations Enhance ecological function by installing large wood features within the restored creek channel. Improves stability, creates varied hydraulic conditions, diversifies creek bed substrate types, and provides fish habitat. Make use of onsite large wood but may need to import woody material. If sediment removal exposes unsuitable substrate (i.e. lacking in gravels and cobbles) may need to import graded stone for riffle and run features.

27 Stephen J. Souza, Ph.D. Princeton Hydro, LLC 1108 Old York Rd, Suite 1 P.O. Box 720 Ringoes, NJ Ssouza@princetonhydro.com