Develop Plans

Approaches to Developing Watershed Plans Using CAST

This framework is offered as one approach for developing a nitrogen, phosphorus and sediment reduction plan for any geographic area within the Chesapeake Bay region. This framework is directed toward developing the Phase 3 Watershed Implementation Plan (WIP), but is applicable to development of other water quality improvement plans. The primary audience is local government planners who will use CAST to estimate the nitrogen, phosphorus and sediment loads resulting from selecting one or more BMPs to achieve their goals. More information on using CAST to develop plans is under How To>User Documentation. Then click on Getting Started in the table of contents.

Steps to Developing a Plan

The following diagram summarizes a sequence of steps for developing a water quality improvement plan.

Steps To Developing Plans

  1. The first step is to establish programmatic goals that include quantifiable loads for nitrogen, phosphorus and sediment; co-benefits from implementing BMPs, and the costs of implementation.
  2. The second step is to translate a combination of programmatic goals into specific BMPs, and then use those BMPs in a CAST scenario to estimate nitrogen, phosphorus and sediment loads.
  3. The third step is to determine if the loads are achieving the programmatic goals. If not, it is necessary to revise programmatic goals, perhaps changing co-benefits and/or costs, and then revising the scenario to estimate loads again.
  4. Once the estimated loads meet programmatic goals, the final step is to finish the plan and send it to the next level of the planning process.

Identifying Goals

Planning Goals for the Chesapeake Bay TMDL Phase 3 WIP

Local area planning goals (LAPG) are developed from the draft Phase III Planning targets for developing the Watershed Implementation Plan (WIP). View more information and download the LAPGs at the link below. 

Planning Goals

Non-Numeric Goals

Reducing nitrogen, phosphorus and sediment while increasing the return on investment requires identifying programmatic goals. Programmatic goals can be identified and then modeled to determine a load reduction. This quantifiable information informs the refinement of the programmatic goals. Many goals may be non-numeric but may imply numeric outcomes. Some programmatic goals can be translated to BMPs.

Examples of non-numeric goals may be a growth policy that includes a regulation on large lot development or zoning requirements. Changes in development strategies are another example of programmatic goals that may be translated to a quantifiable load reduction. Changes in development strategies result in a change to land use. An example is establishing a policy on large lot development that requires a certain percentage to have tree cover. Increased trees or forest land can be modeled with Tree Planting or Buffer BMPs. Land conversion from developed to agriculture can be modeled by Impervious Surface Reduction. Land conversation from impervious developed to pervious developed can be modeled as Tree Planting – Canopy.

Another example is an agricultural regulation on using a Phosphorus Site Index to determine the amount of fertilizer applied. This regulation translates into the BMP Nutrient Management Phosphorus Application Rate Reduction which has a quantifiable effect on phosphorus loads. The programmatic goal in this example is establishing the Phosphorus Site Index as a requirement and the numeric goal is the acres of the Nutrient Management BMP and associated phosphorus load reduction.

Numeric Goals for Nitrogen, Phosphorus and Sediment

There may be programs, policies, or regulations that encourage or require nitrogen, phosphorus and sediment reduction. Planners should be provided with goals, or targets, in one of three forms: percent reduction, pounds of load, pounds reduced. A plan developed in CAST can show the loads in any of these three forms. 

Percent Reduction is available from the Results, Compare page on the third tab. This requires the user to identify an initial condition and compare that condition to one or more plans. CAST shows the percent reduction from the initial condition. 

Total Pounds delivered to the edge of a stream (EOS) or to the tidal waters of the Chesapeake Bay (EOT) on an annual basis is available from the Results, Compare page on the second tab. The total pounds per load source per year is shown for the scenarios selected by the user. An initial condition should be identified and selected along with one or more plans.

Pounds Reduced also is available from the Results, Compare page on the second tab. Just as with total pounds, the user selects the initial condition along with one or more plans. Then the user can simply subtract the difference in load for nitrogen, phosphorus and sediment. 

Numeric goals may be provided at any geographic scale. For example, they could be at the scale of county, state-river basin, or watershed of any size. Plans can be developed in CAST at any of these geographic scales for any area or combination of areas in the Chesapeake Bay Watershed. Results may be viewed and downloaded at any geographic scale as well. Whenever a user creates a scenario or views results, the user is asked to select the geographic scale and area.

The goals may be specified for a particular source sector. Examples of non-point source sectors are developed, agriculture, and natural. The developed sector includes pervious and impervious land in urban areas and rural areas. There is no distinction between new development and redevelopment. The agricultural sector includes pasture, cropped land, animal feeding space and riparian pasture manure deposition. The natural sector includes streams, Chesapeake Bay shoreline, forests and wetlands. CAST input and output is separated into these source sectors. Users add BMPs separately for each source sector and may view results by source sector and for all sectors summed together. 

Reducing Costs and Maximizing Co-Benefits

In addition to nitrogen, phosphorus and sediment goals, there may be additional, complementary objectives. Examples of additional objectives include:

  1. Reducing implementation costs
  2. Prioritizing co-benefits.

Examples of co-benefits include: improve stream health, increase fish habitat, and reduce toxic contaminants. Identifying these additional objectives early in the planning process allows for selection of BMPs that meet the load reduction goals as well as achieve these complementary objectives.

Cost Effectiveness of BMPs

Knowing the BMPs that are most effective and have the lowest cost makes it possible to develop an effective plan. We list in a spreadsheet the typical pounds of nitrogen, phosphorus, and sediment reduced for every BMP. These data are presented in terms of an acre of BMP, or the appropriate unit for the BMP like animal units, feet or acres treated. We also provide the cost of each BMP, and the cost per pound reduced. These data differ by geographical area since there are variable landscape characteristics. To determine the most cost effective BMP, simply filter the table for your geographic area, then sort the table on the cost per pounds reduced for the targeted pollutant. We provide the data at the state and county scales. 

The cost per BMP may differ for each state. The cost data may be downloaded from CAST under the Public Reports > Cost Profiles. Costs are estimated in 2010 dollars. Costs represent a single year of cost rather than the cost over the entire lifespan of the practice.  Costs are annualized average costs per unit of BMP (e.g.: $/acre treated/year). Capital and opportunity costs are amortized over the BMP lifespan and added to annual operations and maintenance (O&M) costs for a total annualized cost. Costs are those incurred by both public and provide entities. Default costs were prepared for EPA using existing data. Bay jurisdictions were provided with the opportunity to review and amend the unit costs for BMPs in the Phase 2 WIP. 

Two graphs are provided for a quick look at the average nitrogen or phosphorus load reduced per sector and the average cost per pound reduced per sector. The agricultural sector is the winner in both cases.  Agriculture has the highest average nitrogen and sediment reduction per acre of BMP implemented (or appropriate unit) and the lowest average cost per pound reduced for the BMPs.

This information is provided to show the relative impact of each BMP. BMPs have a non-linear cascading effect. As a result, your scenario will not show identical load reductions as the table. The actual load reductions depend on the specific BMPs in your scenario, the base conditions for land use, and year. The data do show the relative effectiveness difference among the BMPs.

BMP Co-Benefits

Impacts of co-benefits are described in the factsheets below. Each includes contact information for each state for more information.

BMPs are ranked to indicate their impact on the co-benefits evaluated. This information will be incorporated into CAST scenario results at a later date. In the meantime, the BMP co-benefit impacts are provided at the links below. This scoring matrix can be used in multiple ways:

  • To characterize the additional benefits of their BMP strategy beyond nutrient and sediment reductions. They can use the matrix either to select priority BMPs or to identify the additional benefits of a BMP strategy, especially for BMPs that provide similar nutrient and sediment reductions.
  • To make decisions about which BMPs to adopt based on management strategy priorities.
  • To help sell a restoration plan to local watershed groups and government officials by presenting the additional benefits that can be derived from allocating resources for BMP implementation to reduce nutrient and sediment loads.

It is important to minimize unintended consequences of the matrix. Some BMPs might not be relevant to the user’s predominant land uses and should be excluded from consideration. Similarly, some management strategies might not be relevant to some communities. Communities might want to weight the scores or management strategies to more accurately reflect their local circumstances and priorities. Users should understand that this is an option and that they can include site-specific details about BMPs in the scoring to allow for a more customizable matrix. It is possible that the scoring system will be taken as a final recommendation of the best, or recommended, BMPs. That is not the intent of the matrix. Users should not be overly reliant on the results of the scoring in determining their BMP funding priorities. Because local conditions vary throughout the Chesapeake Bay watershed, no single BMP is the one overall best practice that fits all circumstances. For example, some BMPs are more suited to one land use or soil type than to another. This matrix does not provide that type of information.

Translating Goals to BMPs

Create a Scenario

The starting place for developing a plan for reducing nitrogen, phosphorus, and sediment is to create a new scenario. In CAST, you will be asked to select a geographic scale and area, e.g.: state, county, small watershed, etc. You will be asked to select the initial conditions and wastewater scenario. The Phase 3 WIP is to be developed on 2025 Current Zoning conditions. Select the 2025 Current Zoning base conditions and then select the appropriate wastewater scenario. Wastewater is handled through permits so may not be edited. However, multiple wastewater scenarios are available to facilitate your planning if that is a load that you are considering.

Next, determine the appropriate scenario from which to copy BMPs. The BMPs copied in are your building block. From there, you will add BMPs to meet your planning goal. There are several options from which to select for copying in BMPs. You may choose the latest annual progress scenario. The annual progress scenario includes all the BMPs that are implemented and functioning in that year, regardless of the year in which they were constructed or performed. For example, a 2017 Progress scenario includes cover crops planted in 2017, street sweeping performed in 2017, and forest buffers implemented in any year that are still present and functioning. Selecting a progress as the initial building block allows maximum flexibility. The planner may then remove BMPs that are expected to lose functionality (i.e.: not maintained) and add any BMPs to meet the goals.

Another option is to begin with the last WIP that was developed. The last WIP was the Phase 2 WIP developed on the 2010 initial conditions. Using the previous WIP will get you closer to the goal than the progress. However, the BMPs selected for the previous WIP may no longer be the most appropriate choice. Goals, planning priorities, and the public will to implement certain BMPs may have changed. Better information about the effectiveness of BMPs may have been gained since the last WIP, resulting in a different level of effectiveness for some BMPs. New BMPs and technological innovation may have occurred allowing for better options than were in the previous WIP. Also, the goals may be allocated to sectors or geographic areas differently. If you have other goals, like co-benefits or reducing costs, these may not have been considered in the same way for the previous WIP.

The Phase 3 WIP is developed on 2025 Current Zoning conditions. This means that the number of animals, septics, and amount of each load source (cropland, pasture, developed, etc.) will be different. So not all the BMPs in the Phase 2 WIP may be credited if the BMPs are at the limit of the land, animals, or septics are available. These changes may make it necessary to change some of the BMP selections in the previous WIP.

Beginning with no BMPs is an option, but is not recommended. It is expected that planners have been reporting BMPs to the states, that in turn report the Chesapeake Bay Program, so that the annual progress scenario represents the current condition.

Once the initial BMPs are copied into a scenario and your scenario is created, then you may edit the BMPs to reflect current and planned policies. You may edit the BMPs in the scenario to increase implementation levels, or you may add new BMPs. 

Methods for Adding BMPs to a Scenario

There are three ways you can add BMPs:

  1. Copy from an existing scenario
  2. Upload from a file
  3. Add one by one from the input box on the screen for each sector

Whichever way or combination of ways you choose, you can add BMPs for any geographic scale. CAST allows BMPs to be uploaded from a file. Uploaded BMPs are tab-delimited text files. The downloadable ables below show the list of required columns and sample data for the files. More information is available in the document, Uploading BMPs to CAST.

Considerations for Developing Plans

When selecting BMPs, consider the ability to actually implement these BMPs. Is there the public will? Is there funding? Are the practices voluntary or mandated? A plan should be realistic and have the support of the land owner or responsible party. As such, it is critical that these land holders or responsible parties are included in the plan development process.

To get the largest reduction for the least amount of implementation, consider several factors. First, determine the highest loading load sources and geographical areas. This is where the BMPs can have the most effect. The load sources with the highest initial load is where the greatest opportunity exists for reductions. Likewise, those geographic areas with high loads also have high opportunity for reductions. This may be in a county with lots of agricultural animals, or it may be in an urban area with a particularly high load for various reasons related to how it was developed and the geographic characteristics.

Remember to bring in the information on non-numeric goals, like policies or regulations that can have an impact. Also consider the costs and co-benefits that are important to the community. The BMPs selected should be efficient, maximize return on investment, and improve quality of life. 

Local govenment engagement is critical to implemetnation success. More information about local government engagement is available at the following links.

Local Government Engagement Initiative

Strategic Outreach Education Program for Local Elected Officials


Sometimes users find the names that are used for the load sources and BMPs are unfamiliar. Definitions pop-up throughout CAST when hovering over the names. It may also be useful to download the table of source data that contains all of the load source and BMP definitions. (link to source data page)

In addition, a crosswalk of commonly-used BMP names to the CAST BMP name may be helpful in selecting the CAST BMP that best represents your management action.