Delta flood and drainage

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Agriculture and settlements in deltas commmonly depend on a set of flood defenses and drainage systems to manage water levels. Restoration can either enhance or undermine these systems, and flood and drainage systems may in turn have impacts of ecosystem services. Social acceptance of restoration may depend on our ability to use restoration to predict and enhance flood and drainage function on adjacent lands---

Summary

The ability to accurately predict changes in flooding and drainage of agricultural land as a direct result of restoration project actions represents a key uncertainty in our ability to predict the benefits of these actions to adjacent landowners and community stakeholders in general. Currently there are sea level rise predictive models and hydrologic models that incorporate change in snowpack and participation that describe flood frequency, duration and storage capacity. There are also storm protection models to address impacts to human stakeholders living in or near river delta environments. See Floods and Drainage Methods

Current infrastructure lacks the capacity to adequately handle drainage and store floodwaters as well as providing habitat value

Methods and Issues

Flooding relief and improved drainage are two of the many socioeconomic benefits that river delta restoration projects deliver as valued ecosystem services to river delta communities. Removing levees and levee setbacks reduce inundation periods, increase channel-flow conveyance and increase floodplain capacity as well as improving drainage of properties in the vicinity of river deltas. From a flood-management perspective, there are three ways a project may reduce flooding vulnerability in the community: reducing inundation periods, increasing channel-flow conveyance and increasing floodplain capacity. These benefits are dependent on site specific vulnerabilities related to sea level rise and other climate change impacts so sea level modeling, in addition to hydrodynamic modeling, is often associated with predicting and measuring changes in flood storage and drainage. Monitoring questions relate to a project’s ability to improve the site’s capacity to moderate storm-related flooding and the potential for improved resilience to climate change (Brophy and Van de Wetering 2011).

Policy Relevance

  • Flooding and Drainage is a key concern for coastal communities and the agencies that manage this attribute

Adaptive Management Objectives

The following adaptive management objectives are proposed as part of a Puget Sound river delta adaptive management strategy and are ranked based on three criteria of criticality, viability and policy impact.


FD1. Predict sensitivity to the composition and configuration of conveyance, tide gating, and restoration to maximize field drainage and habitat function in a delta setting

Criticality - We have no toolbox of identifying the combination of live storage, flood gates, and restored estuary that would maximize habitat, flood control, and field drainage.
Feasibility - analysis could be integrated into contract tasks.
Policy Impact - Strategies for organizing flood control and drainage elements could allow for strategic location of restoration and define opportunities to combine agricultural development and restoration funds.

Recommendations for Study

Work To Date


FD2. Develop and reduce costs of robust standard methods to predict the reduction in frequency and/or duration of flood events resulting from project change in flood storage capacity scenarios

Criticality - While project specific methods have been developed there has been limited analysis of how these models meet the needs of stakeholders.
Feasibility - Costs may be high and with complex stakeholder coordination requiring a coordinating partner.
Policy Impact - Understanding would allow strategic placement of restoration sites to increase benefits.

Recommendations for Study

Work To Date


FD3. Develop and reduce costs of robust standard methods to predict the effect of climate change parameters (sea level rise, reduced snowpack storage, reduced precipitation, etc) on future flood frequency and duration

Criticality - While modeling is available it is expensive, and has not been evaluated to meet the needs of delta stakeholders.
Feasibility - Costs may be high and with complex stakeholder coordination requiring a coordinating partner.
Policy Impact - Efficient standard methods would increase the incorporation of climate change in project evaluation.

Recommendations for Study

Work To Date


FD4. Develop and reduce costs for standard method for predicting how tidal reconnection affects field drainage and groundwater salinity at timing important for agricultural stakeholders

Criticality - We do not have a well vetted method for evaluating frequent concerns about how restoration affects groundwater.
Feasibility - Costs may be high and with complex stakeholder coordination requiring a coordinating partner.
Policy Impact - Standard methods would increase support and reduce costs of project development.

Recommendations for Study

Work To Date

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