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What is the Decomp Physical Model?

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The DECOMP Physical Model (Prius v3.5 vs DPM Lite )Fred H. Sklar, Scot Hagerthey & Sue NewmanEverglades DivisionSouth Florida Water Management DistrictGraphics used in this presentation are conceptual only and do not represent the final design of the DPM. These graphics are not self-executing or binding.

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What is the Decomp Physical Model?

  • A pilot study to test engineering solutions for ecological restoration.
  • An on-site, relatively large-scale, controlled manipulation of the environment to evaluate ecosystem response to sheetflow.
  • A landscape manipulation designed to provide critical information of the hydrologic targets for restoration.
  • Provides “ecological lift” to a drained system: An Adaptive Management approach.
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Questions to be answered by a physical model.

Uncertainty 1: Hydrology: Do canals need to be completely backfilled in order to achieve hydrologic restoration?

Uncertainty 2: Sediment: What is the role of floc and sediment movement for restoring and sustaining a stable ridge and slough landscape, and how do canals, levees, and levee modifications affect this movement?.

Uncertainty 3: Restoration: What is the ecological function of sheetflow and what are the hydrologic needs (i.e., flow fields, depths, duration) of the ridge and slough landscape?

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The objectives and issues that make a DECOMP Physical Model (DPM) important.

Objective 1: Evaluate the impacts of sheetflow, weirs, and canal backfilling (partial vs. complete) on the processes associated with the restoration and sustainability of the ridge-slough-tree island pattern in the Everglades.

Issue: Recreational fishing interests do not want canals to be backfilled. However, there is scientific evidence to suggest that canals that are not backfilled will; short-circuit marsh hydrology, interfere with sediment transport, cause water quality problems, and create habitat for exotic fish.

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The objectives and issues that make a DECOMP Physical Model (DPM) important.

Objective 2: Assess the physical and biogeochemical parameters associated with sheetflow as a way to develop, improve and parameterize the tools needed to evaluate Decomp alternatives.

Issue: Hydrologic performance measures for the restoration of tree islands, ridges, and sloughs do not yet include velocity vectors. The NSM is not calibrated for flow fields and no one knows if current peak flow rates of 1 cm/sec can support the biophysics of restored microtopography in the Everglades.

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Objective 2: How much sheetflow is enough?

Present-day Flows

Historic Flows

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What objectives and issues can be addressed with Adaptive Management?

Objective 3: Evaluate the role of floc and sediment movement for restoring and sustaining a stable ridge and slough landscape.

Issue: Wading birds need slough habitats during the dry season for intensive foraging to support nesting and fledging of young birds. Wading bird populations can not be restored if the slough habitats of the Everglades continue to be encroached by sediments, cattails and sawgrass. However, there is no scientific understanding of the biology of floc or its distribution & movement across the Everglades.

objective 3 restore ridge and slough microtopography

As you cross from Ridge to Slough the difference is:

Healthy = 20-30 cm

Impacted = 0-10 cm

The Bedrock Surface is not reflected on the peat surface

Objective 3: Restore ridge and slough microtopography.

Healthy Microtopography

Impacted Microtopography

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3000 ft gap* & canal plug with boat channel)

DPM Prius Concept-

Design linked to “MWD C&SF” features to move water continuously and as pulsed releases along historic flow paths from WCA-3A through large, controlled openings in the L-67A levee, to canal and levee modifications on the L-67C.

DPM Prius Design Factors-

1. A focus on hydrodynamics and sediment movement occurs in a BACI flow-path

2. Long-term statistical variation associated with ecological parameters is handled by a Repeated Measure design.

3. Research schedules are linked to the construction of “MWD C&SF” features.

Prius Model v3.5

3000 ft gap* & complete backfill

BACI Flow-way with one 12,000 ft L-67C levee gap

3000 ft gap* & partial backfill

3000 ft gap* & no canal fill

Repeated

Measure Flow-way

CSOP L-67A weir-culvert cluster location

L-67A Levee

Canal plug with boat channel

L-67C Levee

*Gaps = L-67C levee openings

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3000 ft gap* & canal plug with boat channel

DPM Lite Concept-

Design not linked to “MWD C&SF” or DECOMP features as a result, move water only as pulsed releases along historic flow paths from WCA-3A through controlled openings in the L-67A levee, to canal and levee modifications on the L-67C.

DPM Lite Design Factors-

1. All hydrodynamics, sediment movement, and ecological studies occur in a BACI flow-way

2. Long-term implications are extrapolated from short-term impacts.

3. DPM constructs temporary L-67A features independent of “MWD C&SF” and DECOMP.

DPM Lite v1

3000 ft gap* & complete backfill

3000 ft gap* & partial backfill

BACI Flow-way with one 12,000 ft L-67C levee gap

3000 ft gap* & no canal fill

L-67A Levee

5-6 temporary gated culverts

L-67C Levee

*Gaps = L-67C levee openings

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Differences between Prius v3.5 and DPM Lite v1.

These two models address the same suite of questions. The difference is the degree of statistical rigor, the manipulation of water used to evaluate ecosystem responses and the connectivity between WCA3B and ENP.

  • DPM Lite evaluates short-term hydrologic pulses, while Prius evaluates longer-term geomorphological and ecological responses.
  • DPM Lite evaluates floc movement within short-lived flow fields, while Prius model examines longer-term floc transport.
  • DPM Lite flow fields are limited in their ability to elicit longer-term ecological consequences.
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