Overview

ARIES is built on basic science and our understanding of how natural systems work. The better the data on hydrology, topography, soils, and other determining factors are, the better ARIES can perform. Ecosystem services (ES), such as flood regulation depend on the interaction between natural systems and people. With this in mind, ARIES relies on four types of models, based on GIS and other data: 1) Beneficiary models; 2) Provisioning models; 3) Sink models and 4) Flow models. Initial ARIES mapping and results for the Chehalis River Basin excluded external hydrologic models but utilized locally-relevant GIS data and ad hoc models. Mapping and understanding the beneficiaries, provisioning and spatial flows of floodwater also sets in place the basis for a funding mechanism that can be developed for the Flood Authority.

Practical application

ARIES allowed a fully integrated approach to flood protection, utilizing extensive information from geographic information system mapping and data and will have the capacity to run and test different hydrologic models. River and stream flow and the flood level estimates will be provided with a hydrologic model and based on slope, rainfall, infiltration, impermeable surfaces, snow, temperature, levees, bridges, dams, and other data derived from each subbasin. This will provide water elevation data in each subwatersheds, flood flows and enable simulation of flood protection options, including an analysis of tradeoffs with other co-benefit ecosystem services.

Steps

In the case of the Chehalis River Basin and flood protection, local GIS data was first gathered and integrated into the ARIES GeoServer, which automates the data handling process. Next, preliminary conceptual models for each of the beneficiary, provision and sink region were constructed. Future development of these models will entail closer collaboration with local stakeholders to integrate preexisting hydrologic models. The final maps produced represent preliminary estimates of beneficiary locations and flood protection. Further work to test and integrate external models will improve the accuracy and policy relevance of these ARIES model outputs.

Modeling flood scenarios

The ARIES team is currently developing scenario analysis with actual data from the Chehalis River Basin. A discussion of this planned scenario generation tool follows.

One strength of the ARIES technology is the simultaneous mapping of benefits resulting from ecosystem services, the beneficiaries that receive them, and the flows of water, matter, energy or information that connect benefits or damages to beneficiaries. Because of the mapping of flows, ARIES will be capable of estimating not only the potential provision of ecosystem services, such as flood protection, but also levels of value or damage provided to specific beneficiary groups.

A work session in the Chehalis River Basin, running an ARIES flood scenario analysis would proceed as follows:

1. An operator would select the area of interest, e.g. the upper Chehalis watershed and initiate a baseline ecosystem services flow analysis. This would search the database for locally relevant models and GIS data to populate the source, sink, and use models. These models and the flow model are then run to provide estimates of baseline conditions for actual ecosystem service delivery.
2. The baseline scenario is defined by the in terms of precipitation events, level of ground water saturation and other inputs, and in terms of actions or policies to be simulated on the landscape (e.g. land use changes, construction or removal of levees, etc.). After the baseline and future scenarios have been defined, the model is run. Parameters can include a default hydrologic model developed within ARIES, or, eventually, any desired hydrologic model, which can be “bolted onto” ARIES. Thus, ARIES will be able to use different hydrologic models for scenarios under different model applications.
3. The product of flow analysis is a set of maps that detail the quantity of floodwater that moves across the landscape and either reaches people or property or is intercepted and diverted. The model could compare scenarios with changes in land use patterns, elevated structures, increased forest cover, greater permeability to groundwater, construction or removal of dams, levees, roads, bridges, or other potential scenarios.
4. Because ARIES models individual beneficiaries it can compute the precise areas of flood protection provisioning or source flood waters that affect them. In this way, the fine-grained effects of policy or global changes can be studied with scenarios, both overall and on a location-specific basis.
5. Because ARIES computes other terrestrial ecosystem services besides flood protection (carbon sequestration and storage, water supply, sediment regulation, aesthetics, recreation), the overall value of each scenario can also be compared at a glance showing the influence on other ecosystem services and their beneficiaries.
6. ARIES also computes not only the provision of each ES, but also the fraction of benefits that actually reach beneficiaries (and the explicit spatial routing of this provision), the efficiency of provision (the ratio of the potential benefit that is actually used) can be calculated under each scenario. This can then be compared to other flood protection investments, or any combination of flood protection investments to show how much benefit was received by which beneficiaries across the landscape and how efficient or co-dependent each investment was in providing these benefits. These benefits could be measured as fewer residences flooded, less economic damage, lowered flood water elevations, fewer people and economic assets in the floodplain and in danger of flooding.
7. In addition, ARIES provides measures of uncertainty. Though two forest areas or structures may be identified as providing flood protection the levels of certainty in provisioning may be different. Uncertainty can be shown as data or mapped.

A scenario generator will change the model parameters based on user inputs for different actions in subwatersheds such as construction or removal of a levee, dam, or elevated structures, land use changes or increased retention from wetland restoration or other flood protection actions. These scenarios can be combined with different rainfall and flood source scenarios to provide a variety of flood scenario combinations. With this, the Flood Authority or other users can test the robustness of one flood action with different rainfall, temperature, snow, groundwater saturation states.

Please contact Earth Economics with your questions and feedback.

Email: info@eartheconomics.org

Phone: +1 (253) 539-4801

Click HERE for a full report on the ARIES application to flood regulation in the Chehalis River Basin.