Milestones in the development of GENESIS

GENESIS version 2 was initially released in December 1989 and represented the first public release of the GENESIS model. Technical documentation of the GENESIS model was provided with this release of the model in Technical Report CERC-89-19 (Report 1), Hanson and Kraus, 1989, and is commonly known among GENESIS users as the "Technical Reference" manual. In September 1991, GENESIS version 2.5 was released together with the GENESIS system support programs. Technical documentation with step-by-step example applications of each of the GENESIS system support programs was provided in Technical Report CERC-89-19 (Report 2), Gravens, Kraus and Hanson, 1991, and is commonly referred to as the "GENESIS Workbook." The GENESIS system support programs were developed to automate many of the tasks associated with conducting a design level numerical shoreline evolution investigation using the GENESIS model. The motivation for the development of the system support programs, was a recognition of the requirement to utilize computer programs to develop the required input data streams necessary to run the GENESIS model, and the need for standardization of analysis procedures and techniques which access standardized data bases (e.g., Wave Information Study wave hindcast data bases, Hubertz, et.al. 1993), or output from other numerical models (e.g., RCPWAVE), and generate intermediate analysis results or direct input data streams for GENESIS. In August 1992, the GENESIS system support programs, the numerical models GENESIS and RCPWAVE, together with model configuration data editors and graphics programs for GENESIS and RCPWAVE, were released in an integrated menu driven system known as the Shoreline Modeling System (SMS). A user's manual for the SMS was provided in Instruction Report CERC-92-1, "User's Guide to the Shoreline Modeling System" (Gravens 1992).

Development of the GENESIS model has continued based on identified needs for model improvement brought to light through application of the model to increasingly diverse coastal settings. The release and distribution of the present version of the GENESIS model referred as version 3, includes several model upgrades and enhancements that have been developed since the release of GENESIS version 2.5. A summary overview of the model upgrades is given in the following and formal documentation will be prepared, published, and disseminated upon completion.

GENESIS Version 3 - Upgrades and Enhancements

The major upgrades and enhancements included in version 3 of the GENESIS model can be categorized into four topic areas.

1. New algorithms for wave diffraction and different procedures for computing the cumulative effect of multiple wave energy sources impacting a given shoreline reach.
2. Addition of a moving shoreline position boundary condition.
3. Addition of the capability to simulate mechanical sand bypassing operations within the model domain.
4. Incorporation of an improved representation of groins and jetties.

A summary of each of these model upgrades or enhanced capabilities are given in the following.

Wave diffraction and the cumulative effect of multiple wave energy sources.

The concept of wave energy windows is central to GENESIS and determines its algorithmic structure. Wave energy windows provide a powerful means of describing breaking wave conditions alongshore and the associated sand transport for a variety of configurations of coastal structures. For a complete description of the concept of wave energy windows, sand transport calculation domains, and multiple diffraction see pages 77-80 in the Technical Reference. As originally formulated, breaking wave conditions alongshore were individually computed for each wave energy window. The resulting shoreline change was computed based on a summation of longshore sand transport rates calculated from each of the energy windows. This calculation procedure was found to result in unrealistic shoreline evolution in instances where multiple wave energy windows influenced the same sand transport domain and some energy windows were inside (landward) of the breaker line while other energy windows were outside (seaward) of the breaker line. The enhancement discussed here has changed this calculation procedure. The new procedure involves computing a single energy-based breaking wave field along the entire model domain prior to calculating sand transport rates and the resulting shoreline change. This means that instead of summing sand transport rates for a reach of shoreline influenced by multiple wave energy windows, an energy-based sum of the various breaking wave fields (one for each wave energy window) is first computed and then sand transport rates are computed only once and shoreline change is subsequently calculated. This model enhancement, is confined entirely within the computational portion of the model and requires no additional model input.

Moving shoreline position boundary condition.

As originally formulated the GENESIS model allowed for the specification of two distinct lateral boundary conditions, the "pinned-beach" and the "gated" boundary conditions. For a complete discussion of these boundary condition see pages 41-42, 86-89, and 99-101, in the Technical Reference. In many applications involving simulation of shoreline change it is possible to identify portions of the beach that might serve as model domain boundaries which are moving with a fairly constant rate. In those cases, the two originally available boundary condition formulations in GENESIS are not appropriate. The moving shoreline position boundary condition upgrade addresses this model weakness by generalizing and expanding the originally formulated "pinned beach" boundary condition. The pinned beach boundary condition is equivalent to a moving boundary at which the movement is specified as zero. Implementation of this model upgrade requires additional input data not previously required. The new model inputs are specified in the START file on lines C.4 through C.12. The START file distributed with the GENESIS software reflects these additional input lines which are self-explanatory.

Mechanical sand bypassing.

This capability is analogous to including point or line sources or sinks of sand within the model domain, but in practice this is most often associated with mechanical sand bypassing operations and is consequently referred to as such. The model upgrade allows the user to specify point or line sources or sinks of sand anywhere within the model domain. Implementation of this model upgrade within GENESIS again requires input data not previously required by the model. As implemented specifying bypassing operations in a given GENESIS simulation can be done in one of two ways, either entirely within the START file, or through the use of an additional input data file called "BYPASS" together with specific entries in the START file. Within the START file, model inputs regarding specification of bypassing operations are contained in section "J" which includes entries for ten specific data values or arrays. The START file distributed with the GENESIS software reflects these additional START file input lines and are self-explanatory. Also distributed with the GENESIS software is an example BYPASS data file which can be used as a template for generating additional BYPASS data files.

Improved representation of groins and jetties.

Groins and jetties have been represented in GENESIS throughout its development, and shoreline change has been successfully simulated for cases involving jetties and groins in the field and in physical models. However, predicted shoreline response adjacent to groins has been regarded by the GENESIS model developers as needing improvement, particularly for groins that are both permeable and diffract waves. The groin boundary condition enhancement included in GENESIS version 3 was revised based on the following three requirements:

1. Bypassing should be represented such that the shoreline response to a groin, including evolution of the shoreline in time and its equilibrium plan form, depend on groin length (actually, depth at tip of groin since a specified profile shape is assumed), with an increase in length increasing the impact of the structure on the shoreline.
2. Different groin permeabilities should produce different equilibrium plan forms, with increasing permeability decreasing the impact of the structure on the shoreline.
3. A permeability of 100% should result in longshore sand transport and shoreline evolution identical to that with no groin present.

This model enhancement is contained entirely within the computational portions of the GENESIS model and requires no additional model inputs. In fact, a previously required model input (START file line F.2) variable "SLOPE2", representative bottom slope near groins, has been eliminated. Previous versions of GENESIS used this input specification to compute the depth at the tip of the groin which is required to calculate the magnitude of sand bypassing seaward of the groin. In GENESIS version 3, an equilibrium profile shape of the form y=Ax**(2/3) is used to calculate the depth at the tip of the groin. The sediment scale parameter " A " is calculated using user-specified grain size information input to the model.

Comments and Questions.

Each of the above described model enhancements and upgrades have been implemented and tested by CERC personnel and others to the extent possible. However, because the model allows, in effect, an infinite number of possible coastal configurations it is possible that a unrealistic representation of shoreline change could occur as a result of a specific model configuration. If this should occur, or if you have questions regarding the model formulation, or if you require clarification or additional information regarding the GENESIS version 3 model enhancements and upgrades, please contact Mark Gravens by phone at (601)634-3809, or fax at (601)634-4314, or Email at m.gravens@cerc.wes.army.mil, or by mail:

USAE Waterways Experiment Station
Mark Gravens (CEWES-CR-P)
3909 Halls Ferry Rd
Vicksburg, MS 39108-6199