Technical data

Gathering Data for Hydrologic Analysis

When evaluating a site to determine whether development is feasible,

you must consider what effect the development of the site will have

on the area’s runoff amounts. The first step in this process is to gather

hydrological data about the site, primarily for the pre-development

model. You must have an existing ground surface, and you must know

the soil type and current land use of the site.

You can start the watershed hydrologic analysis by using the

Terrain ➤ Terrain Model Explorer, located in the AutoCAD Land

Development Desktop, to create an existing ground surface model

of the site. Then, you can use the watershed command (also within

the Terrain Model Explorer) to create polylines that outline the

principal watershed areas on the surface model. Later, you can

select these polylines when prompted to choose a watershed area

when using the Hydrology commands. Soil type information,

including soil boundary information, can also be added to your

surface model.

Key Concepts

■

Before starting a hydrologic analysis of a site, determine the

hydrologic soil groups existent at the site, the cover type,

treatment, and hydrologic condition. These features will affect the

results of the pre-development runoff calculations.

■

A good way to start the hydrologic analysis of a site is to use the

Terrain Model Explorer to create a surface model, complete with

topographical information, watershed boundaries, subarea flow

paths, slope arrows, and relevant hydrologic data.

■

Your compiled topographic and hydrologic data should extend

sufficiently off-site to provide adequate coverage of the drainage

area affected by your proposed development.