The water cycle - groundwater and surface water

Through evaporation on the surfaces of the oceans and the land
constantly releases unimaginable quantities of water into the atmosphere.
When cooled, the water vapor condenses into clouds and finally falls back to the earth's surface as
dew, rain or snow on the earth's surface. Some of it runs off or
evaporates again, much seeps into the upper layers of soil and is absorbed by plant roots.
and is absorbed by plant roots. The rest seeps deeper, following
gravity until it reaches impermeable layers. Due to the
impermeable layer, the pores of the soil above it fill up to the surface.
soil above it fill up to saturation: Groundwater forms.

In sloping terrain, the groundwater begins to flow until it returns to the surface as a spring at a
until it rises to the surface again as a spring at a lower point. In our area, groundwater often emerges over large areas without a clearly recognizable
emerges as a seepage spring. In most cases, a typical plant community known as a
typical plant community known as a spring swamp. Less common here is
rarely to be observed at the bottom of small spring depressions, bubbling water rising in funnel
or pot springs can be observed. Excavations and boreholes in which groundwater has been tapped by human activity are called wells.

After reaching the surface, the spring water flows downhill as a stream following the slope of the terrain.
down the slope as a stream. By joining several streams, a river is formed that can always take in new tributaries or flow back into a larger river. Following a non-binding custom, a river that flows into a sea is called a stream. Ditches are often created as artificial watercourses to drain high groundwater. These often do not exist all year round or even only for a short period as temporary watercourses. Large parts of Offenbach's
forests and many agricultural areas are criss-crossed by such drainage ditches created in earlier centuries. Plant communities similar to those on the banks of streams and ponds have developed along their edges, so that they are only recognizable as artificial bodies of water due to their straight course.

Waters that are completely surrounded by solid land are called still waters or standing waters.
or standing waters. Inflow and outflow are of secondary importance compared to the volume of standing water.
importance. Standing bodies of water form naturally in depressions with no outflow, the bottom of which lies below the groundwater table. Sections of watercourses can be separated by soil displacement during flooding or construction work. This creates a special type of standing water, the oxbow lake.

Almost all of Offenbach's standing waters were created by human intervention: They were created by extracting the gravel, sand and clay deposits deposited by the Main River to below the groundwater table, and some were also created by damming small streams. Since 1997 , several shallow ponds have been created for amphibians, dragonflies and water beetles in waterlogged soils in the south-east of Offenbach. Ecologically valuable wetlands have developed here within a short space of time. In the forest to the south of Offenbach there are smaller, circular ponds that were created during the Second World War by the detonation of heavy explosive bombs. Many of these bomb craters were backfilled with excavated earth, building rubble and waste shortly after the end of the war and during the heavy construction activity up to the end of the 1950s , while species-rich aquatic biotopes were created in others. In contrast, artificial bodies of water sealed with concrete or sheeting are of little importance for flora and fauna. Only a constant supply of water and cleaning can maintain unstable biotic communities that are susceptible to disturbance.

High groundwater levels with intermittent flooding and a good supply of nutrients
in the soil leads to the development of special vegetation in which rushes, bulrushes, sour grasses or reeds characterize the landscape and marsh iris, meadowsweet, purple loosestrife and marsh marigold form colourful spots. Such habitats are known as marshes. If the soil is firm enough to provide sufficient support for waterlogged trees such as alder or birch, a swamp forest can develop here.

Wet areas over nutrient-poor soils promote the occurrence of undemanding peat mosses, in whose cushions other rare plants can also develop.
plants can develop. If the water level remains high, the
peat mosses can form thick layers that continue to grow upwards,
while they die at the bottom without rotting completely. Thus
initially creates a fen, which can gradually develop into a raised bog.
can develop further.

Status August 2021

Text taken from the brochure "Offenbach and its waters - a relationship spanning more than a thousand years" from 2016