Delmarva Unit Hydrograph
The NRCS dimensionless unit
hydrograph and the NRCS triangular unit hydrograph are widely utilized in the
United States to develop storm hydrographs for evaluating and designing soil and water resources management practices. These unit hydrographs are based
on a standard set of assumptions and are commonly used to model water flow in various hydrologic systems. However, in some regions of the country,
such as the Delmarva Peninsula, the local topography is relatively flat, and
there is a large amount of surface storage available. As a result, the shape of
the observed storm hydrographs in these areas can differ significantly from
those generated using the NRCS unit hydrographs.
To address this issue, a unit hydrograph
known as the Delmarva unit hydrograph has been developed and used by utilities
in Delaware, Maryland, Virginia, and some parts of New Jersey. This unit
hydrograph is similar to the NRCS dimensionless unit hydrograph, but it has
been modified to better represent the runoff characteristics of the Delmarva
Peninsula. By using the Delmarva unit hydrograph, utilities in these states can more accurately model the flow of water in their systems and better
understand the impacts of various soil and water resources management
practices. Overall, the Delmarva unit hydrograph is an important tool for
helping to improve the management and conservation of water resources in this
region.
Qp = 284 * A / Tp
where
Qp = peak flow rate in cfs.
A = area of the watershed, in square miles, draining to the location of the unit hydrograph.
Tp = time to peak of the unit hydrograph in hour
Time to peak, and lag time are calculated according to Equations 97 and 98, respectively. When compared with the NRCS methods, the Delmarva unit hydrograph produces lower peak flow rate but yields the same flow volume.
