Conservation Prioritization Tool for Source Water Protection

F oothills Conservancy of North Carolina 

 Catawba Lands Conservancy 

 The Conservation Fund of North Carolina 

Collaborating with the Catawba-Wateree Water Management Group (CWWMG), a consortium of the 18 drinking water utilities and Duke Energy that operate within the Catawba-Wateree watershed, and the Catawba Wateree Initiative, a partnership among conservation organizations, we undertook the development of a watershed scale conservation prioritization framework. Eleven hydrologic metrics plus sediment loading projections were used identify land areas that, if developed, were most likely to adversely affect water resources. 

Based on these metrics, an economic valuation model was used to estimate the avoided costs and multiple ecosystem service co-benefits of protecting natural lands within the watershed.

Together these methods provide a quantitative framework to evaluate and compare the costs and benefits of protecting natural lands that are at high risk of development. This framework can then be used to prioritize conservation and land protection decisions and investments.

A first version of the framework was developed with funding support from the Water Research Foundation (WRF), the U.S. Endowment for Forestry and Communities, and the CWWMG. The results of that initial application specific to the Catawba-Wateree watershed are available as a WRF report (Eddy et al., 2019). Recent updates to the framework, using more recent land cover data and more sensitive land use change model, were funded by the CWWMG and are  documented here .

1. Estimate potential changes in flow and sediment delivery from the watershed as a result of future change in climate, land use, and water use.
2. Find areas in the watershed where the impact relative to other areas is disproportionately large (“hot spots”).
3. Determine if and to what extent land conservation of “hot spots” could mitigate some portion of the total downstream impact to water supply.
4. Estimate the economic benefits of the mitigation and combine with “hot spots” for watershed prioritization.
5. Provide supplemental benefits of currently conserved lands.
6. Guide stakeholders in using the maps, values, and summaries in planning, application, and education activities.

The figure below highlights the three main ways in which this framework may be used. With Watershed Planning there is the option to take a look at “big picture” happenings across the whole Basin. When using the framework for Local Decision Support, a user can dig right into the data assessments for their area of interest. And finally, the framework allows a user to Reassess to Answer Your Questions based on the projected changes to the hydrology and water quality in the Basin.

Scroll through the screens below to step through the three main steps of the framework. 

Daily values of modelled streamflow and water quality provide little meaning without context and simplification. Metrics summarize these time series as single values that can be more easily compared and evaluated to characterize stakeholder priorities. However, a vast range of metrics exist to quantify distinct perspectives of the hydrologic regime, typically regarding the intensity, duration, and frequency of flow events. For the conservation framework, a set of metrics must be selected to reflect priorities and areas of interest in the hydrologic regime.

In summary the steps are:

• Review the metrics.
• Decide which metrics influence your hydrologic and/or water quality concerns.
• Assign weights to your selected metrics to form your priority index.
• Review priority scores by catchment where scores > 25% indicate hot spots for your objective.

A mitigation scenario is used to assess the opportunity to lessen the impacts of the future changes with conservation. The scenario is created by holding current natural lands constant in the future projected land use scenario while the remaining areas of the watershed develop or increase in development intensity. The scenario is not meant to be prescriptive of a true future but is rather used as a means to calculate the mitigation of future hydrologic and water quality changes on a local basis.

To assess the economic benefits of land conservation in each catchment, we analyzed and estimated monetary values for five main categories. Three of the benefit categories—water-based recreation, lakeshore property values, and avoided drinking water treatment costs—are derived from improved water quality in the mainstem reservoirs, due to avoided sediment runoff from land in the watershed. The other two categories of benefits—carbon storage and air-quality-related health benefits—are specifically provided by trees and forest cover in the watershed. For catchments containing natural lands with a high likelihood of development by 2050, we estimated the average per-acre benefits of conserving these natural lands. 

In addition to the per-acre benefit values shown above, the average costs per acre of natural land, based on tax assessed values, were used to derive a net benefit for each catchment. Combining these net benefits with the previously determined hot spots provides a Basin-wide action plan for conserving lands that derive the most economic benefit while addressing the objectives of the hot spot assessment.

The caveats to these final steps are that the costs values generated for this study may vary greatly from the actual costs to the organization seeking to conserve the land given the various options available besides outright land purchase and the range in tax assessed values. Also, when prioritizing across hot spots, as noted previously, the hot spots are identified according to the objectives set when selecting metrics to calculate the Priority Score. Therefore, the hot spot locations may change between assessments.

The power of this framework is that users have the flexibility to define their own objectives when prioritizing local areas within the basin most at risk from projected changes to water resources. Since the user decides which hydrologic and water quality metrics and in which combinations to use when scoring the changes, they define their own assessment with a targeted objective (e.g., reducing risk of flooding or increased sediment loads to surface waters) to locate hot spots. Defining a specific assessment requires interaction with and calculation using the data outputs from the model. To provide more actionable information to users, we have created an interactive user tool to give users direct access to the mapped results for a set of assessments with no analysis effort needed.

The user tool linked below provides a series of pre-defined assessments in which the metrics, weighting, and final priority score have been completed and used to display the hot spot maps for user exploration. These assessments were chosen to target different source water protection objectives of interest to the local stakeholder community. The objectives range from maintaining current conditions to protecting baseflows to trying to limit floods. By viewing the catchments or local areas identified as hot spots within each assessment, a user can learn how critical different areas are to preserving certain water resources. Conversely, a user may know exactly which area they wish to assess and use the maps to know which source water protection objectives can be addressed by conserving lands within that catchment.

The user guide provides an overview of the tool ( located HERE ).