Water Retention

Introduction

The topics on this page include natural and human-build modes of water retention from ponds and dams to aquifers.

Some types of water retention such as aquifers can exist for thousands, even millions of years. Other retention options listed here such as swales may only help to sequester water for short periods of time after precipitation or a thaw. They may also need frequent servicing such as silt removal, re-digging, or repairs.

Underground Storage

Aquifers

These are natural water stores beneath the Earth's surface. They take thousands of years to recharge, but humans (particularly farmers) have been pumping them dry at record speeds, causing the ground to sink, which in turn causes structural damage to homes, roads, and even dams.

According to this paper, trees are important for helping to recharge aquifers, so tackling deforestation, and planting more trees may be key to stabilizing aquifer levels in the long term. 

Trees have been shown to help recharge aquifers by encouraging water penetration with the paths provided by tree roots. 

Some governments have found that the best short-term solution to land subsidence is to ban well use and ground water pumping within certain areas. In Saudi Arabia for example the growing of livestock feeds such as alfalfa has been banned to help protect their dwindling groundwater supplies.

Underground Cisterns

Our ancestors used underground caverns to store large amounts of water in often ornate cisterns which are still in use around the world today. 

Thanks to modern technology, we can now dig holes much more easily and install prefabricated cisterns made from concrete, plastic, or other sturdy materials.

Ground-Level Storage

Ponds & Lakes

These can be natural or artificial, and double as valuable ecosystems and water sources for wildlife. Plant life can help keep water clean and wildlife including frogs, dragonflies, and fireflies can help keep pest species like mosquitos under control. Ponds and lakes can be important for humans as they can improve mental health, provide resources such as food and crafting supplies when they are allowed to host rich biodiversity and are kept clear of invasive species.

Lakes and ponds can have artificial liners, but natural lining such as clay with soft or gravel bottoms can help support wildlife and their larva (for example fish and dragonfly larva). If you don't have much room, even a tiny pond can help local animals find a place to drink and cool down. 

Rain water can be diverted from places that frequently flood to help fill these ponds naturally, preventing run off and sequestering the rain water for drier parts of the year.

Berms & Swales

Berms are raised portions of dirt used to hold small amounts of water, and swales are the accompanying dug channels that help transport water to a better location. Swales can exist on their own, but if on a slope, the dirt dug from the swale can be used to build the berm, which will help capture water going down the incline. Swales are designed to transport intermittent water from precipitation along a gradient.

The outer edge of the swale or berm should have a dip in an appropriate locations to serve as a spillway. In a garden with a swale diverting water from a downspout to a roadway, the spillways would best be placed along flower or produce beds.

Dams & Reservoirs 

These can provide energy, preserve drinking water. These can be vital for retaining water in drought-struck regions, however damming systems can break up and harm aquatic eco systems which endangers many species of fish and amphibians. They can also rob water from delicate ecosystems resulting in toxic salt lakes and desertification elsewhere in the landscape. These changes can in turn result in water shortages and loss of income for communities that relied on water that dams may hoard.

Beaver Dams

Beavers are Nature's engineers, slowing water ways and sequestering moisture even in drier regions. They've helped bring back rare plant and bird species when reintroduced to their historical ranges, and have proven to be important allies in the fight against increasing wildfires.

They are native to much of North America including Canada and the USA, as well as Eurasia from Portugal and Wales through Norway and Russia all the way to northern Mongolia and Eastern China. It is believed that their introduction to Ireland would be beneficial to the country, but "there is no evidence that beavers were ever present in Ireland and so, unlike Britain, this would be an introduction rather than a reintroduction." Another detail to consider is that since beavers tend to live in wet conditions, the lack of skeletal remains may be due in part to poor preservation conditions, rather than solid proof that there were never any beavers in the country.

Beaver Dam Analogs (BDAs)

BDAs are human-made approximations of beaver dams. They are short and made of permeable materials including sticks, branches, and packed mud. Humans copy beaver building methods to help slow waterways and create contentions which can function as breeding pools for endangered fish, while helping to sequester water for the entire landscape. 

Much like beaver dams these can help fight flooding and fires. They are also cheap and fairly easy to install, opposed to modern, dams which need heavy duty equipment, cement, permits, and other costly basics to build and maintain to prevent deaths and damage in major weather events. By contrast BDAs can and are even expected to be destroyed during heavier events, or simply with time, without doing significant damage downstream.

Weirs

"A weir is a small barrier built across a stream or river to raise the water level slightly on the upstream side; essentially a small-scale dam. Weirs allow water to pool behind them, while allowing water to flow steadily over top of the weir.[2] Additionally, the term weir can be used to refer to the crest of a spillway on a large embankment dam.

Weirs can be constructed out of several different materials, depending on their age and purpose. Wood, concrete,[3] or a mixture of rocks, gravel, and boulders can all be used to construct a weir.[4]

In a weir, the surface over which the water flows is known as the crest. The flow of water that moves overtop of this crest is known as the nappe, which is simply the water that makes it overtop the weir. This nappe does not exist with dams, as dams permit no flow of water over the structure. If this nappe falls a significant distance through the air - meaning that the weir increases the elevation of the water prior to the weir - the weir is said to have free discharge. However, if water flows partially underwater as a result of little elevation increase from the weir it is said to be submerged or drowned.[5]" - Energy Education

Step Wells / Baoli / Baori

These ancient structures were once the common meeting place for Indians to collect drinking water, bathe, socialize and hold important ceremonies. Today many have been abandoned in place of indoor plumbing, but as local water scarcity and pollution is becoming a greater problem, communities are beginning to dig out and fix their local stepwells. Each year these giant stepwells capture monsoon rains, maintaining a safe water supply year-round.

Click the Harvesting Water button to learn more, including guides for stepwell restoration, and organizations working to save them.

High Altitude Storage

Ice Stupas

Water Towers

These don't exactly count as part of a SUD system (which was the original topic of this page), but they do count as a form of artificial water storage. The high storage level of the water creates pressure that is useful for communities to maintain a pressure that is useful for showers and hand washing.

Organizations

Oceana

Australia

Maps

North America

USA

Grants

North America

USA

Minnesota

Related Topics

Water & Hydrology

Click the Water button to learn about water use and scaricity in general.

Harvesting Water focuses on the many ways we can harvest water, for human or animal use.

Flood Management & Rain Harvesting focuses on the many ways water can be diverted and saved, at the same time reducing erosion and downstream flooding.

Water for Wildlife

Our Water Options page focuses on ways to provide water for wildlife including bird baths and ancient designs such as dew pools.

The Aquatic Rewilding page focuses on the many aquatic biomes and some of the things conservationists are doing to help protect and restore them to their natural glory.