PGDM Inland Flood Hazard Map: Camps River, Nevis

A higher resolution map image is also available (JPG 690k)

Map Text

The flood study determined the flood extent and the water depth variations caused by 24 hour rainfall events at three return periods--1 in 2 year, 1 in 10 year, and 1 in 100 year. The map on the extreme left shows the flood envelopes and the maps on the right each shows the variation of water elevations within the flood envelope for a specific return period.

1. The boundary of this flood study is shown. Within the boundary is the Camp River road crossing immediately west of Nisbett Plantation. The extent of flooding and the variation of water depths at different return periods at this bridge are shown in the maps.
2. Detailed surveys, including bridge details, were conducted along the Lower Camp River at about 25 metre intervals along the watercourse. This information was supplemented by elevation data taken from a 1:2500 contour map and used to build a digital elevation model (DEM) of the river and its floodplain.
3. It is evident that Nevis Island will experience the same high intensity storms observed on St. Kitts. Owing to the unavailability of a substantial rainfall database for Nevis Island (only 1 year of rainfall data was available) rainfall for St. Kitts was used to derive the critical storm and subsequently the critical runoff hydrographs for the1 in 2, 1 in 10 and the 1 in 100 year rainfall. However, the resulting flood map must be regarded as preliminary and should be updated as soon as data from Nevis become available.
4. Only daily rainfall values were available, so hourly intensities for peak flow determination were derived using the Type III temporal distributions from the National Resources Conservation Service (formerly the Soils Conservation Service), United States.
5. Estimated water levels were derived using the HEC-RAS hydraulic model, Version 2.2, The United States Army Corps of Engineers. Interviews conducted within the Lower Camp River Watershed provided historical water level elevations and these were used as a rough guide for model validation. Updating these water level estimations must be accompanied by field measurements of water levels for specific flooding events.
6. The water level estimates were based on the following assumptions: (i) the bridges and watercourse were inadequately maintained, such as was observed during the field visit in October, 2000; and (ii) a fully saturated watershed with water already on the ground from previous rainfall 24 hours earlier.

USE OF THE MAP

Owing to limitation in the rainfall data and the lack of information on water levels from actual storms, these maps must be regarded as preliminary only.

Used in conjunction with the island flood map, these maps can be used to provide improved definition of the extent of the 1 in 100 year flood boundary within this watershed.

The map provides rough estimates of the variation of water depths within the floodplain for various return periods.

From the water level variation maps, an estimate of the expected water elevation for various rainfall magnitudes can be obtained. Thus, the map can provide a preliminary basis for determining the bridge elevation required to replace the sunken bridge at Nisbett Plantation.

Survey and Map Information

Grid: British West Indies
Projection: Transverse Mercator
Latitude of Origin: Equator
Longitude of Origin: 62 deg 00 min West of Greenwich
Scale factor on central meridian: 0.9995
False co-ordinates of Origin: 400 000 metres East, nil North
Unit of measurement: metre

Detailed surveys along Camps River were conducted by Dwight C. Francis, Saddle Village St. Kitts.

Controls points obtained from the Land and Surveys Department, St. Kitts/Nevis Government, were used for placing the survey data on the National Grid.

Dated August 2001.