Latest revision as of 12:13, 22 December 2015

Improve water retention

Category 01. Water flow quantity improvement

General description

Water quantity and the flow regime can be altered by different factors such as changes in land cover, soil structure and compacting, loss of floodplains and wetlands, and stormwater runoff from urban areas. Loss of water retention combined with accelerated runoff typically increases the frequency and magnitude of flood peaks but also reduces the availability of water to streams during the prevailing low flow (base flow) periods.

Preferably, a more natural flow regime can be restored by increasing water infiltration and retention at the catchment scale as described here, by e.g. changes in land cover and floodplain restoration, since this addresses both, increased peak flows and reduced base flows. When space is limited, an alternative local end-of-pipe solution to reduce peak flows caused by stormwater runoff are retention and detention basins (see Improve Create water storage).

The measures to improve water infiltration and retention may be applied in combination with other restoration measures (e.g. water storage, restoring side channels or former meander is firstly done for restore channel morphology and lateral connectivity but also increases infiltration area) at different spatial scale and location (riparian zone, nearby land, etc). Some techniques to improve water retention and infiltration are:

• Changes in land use and cover
• Reduce and limit the amount of impervious surfaces in the watershed

• Change land use practices and zoning regulations to limit the allowable percent of impervious surface in the watershed

• Decommission roads

• Use pervious pavement alternatives where feasible

• Minimize the extent and degree of soil compaction and improve soil infiltration and retention capacity
• Restore stream connectivity to floodplains (see Remove bank fixation, Allow/increase lateral channel migration or river mobility, Remeander water courses, Shallow water courses, Widen water courses, Lower river banks or floodplains to enlarge inundation and flooding, Remove hard engineering structures that impede lateral connectivity, Set back embankments, levees or dikes )
• Revegetate denuded areas within the watershed. Mean annual flow is increased as a result of greater runoff due to clearing and urbanization (Peterson& Kwak 1999)
• Protect, restore, and create wetlands and other infiltration areas (see Construct semi-natural/articificial wetlands or aquatic habitats, Improve backwaters, Reconnect backwaters and wetlands, Restore wetlands, Retain floodwater )

Applicability

Changes in land use and cover

Watershed treatment involving the establishment of tree, bush and other plant cover is widely used as a way of reducing runoff and increasing infiltration. However, the effect depends on the balance between improvements in infiltration caused by increased vegetation and relative changes induced in evapotranspiration (ET). There general thought that more trees mean more water is a wrong assumption. Cover change from species of lower to higher ET would lead to a decrease on mean surface runoff and annual flow. A change to species with lower ET would increase mean surface runoff; a reduction of forest cover increases water input to watercourses. However the impact depends on the management practices and the alternative land uses. Mean flow after the development of new vegetation could be higher, the same or less than the original value, depending on the type of vegetation (Bruijnzeel, 1990). The conversion from forest to pasture leads to a decrease of ET, an increase on surface runoff, base flow and total stream flow (Fuhrer et al., 2000). The conversion into forest would have the opposite effect, but when we are thinking on improving water retention,we should consider the role of vegetation for improve soil infiltration (especially deep rooted trees) but remember that the roots are more like pumps that sponges, and that it is the soil that stores water, not the trees (Hamilton et al., 2008).

Source: Extracted from Bruijnzeel, 1990.

Minimize the extent and degree of soil compaction and improve soil infiltration and retention capacity

Expected effect of measure on (including literature citations):

• HYMO (general and specified per HYMO element)

Replacement of conventional pipe stormwater systems by bio-filtration stormwater management leads to a decrease on urban runoff, lower peak discharges, delay on stormwater discharge, and shorter duration (Lloyd et al., 2002).

• physico � chemical parameters

Concentrations of Total Suspended Solids (TSS), Total Phosphorus (TP) and Total Nitrogen (TN) discharged from the bio-filtration system are typically lower than pollutant concentrations discharged from the piped system (Lloyd et al., 2002).

• Biota (general and specified per Biological quality elements)

Temporal and spatial response

Pressures that can be addressed by this measure

• Hydrological regime modification
• Groundwater abstractions
• Surface water abstraction

Cost-efficiency

Stormwater Best Management practices have a good cost-efficiency. Replacement of conventional pipe systems by bio-filtration systems supposes little increase on project implementation and brings environmental, economical and social benefits (water quality improvement, aesthetic and recreational values).

Case studies where this measure has been applied

• Renaturierung Untere Havel
• Vääräjoki - Niskakoski
• Kuivajoki - Hirvaskoski
• Spree - Restoration and remeandering of the Müggelspree - downstream Mönchwinkel
• Regge Velderberg
• Millingerwaard - Floodplain rehabilitation
• Vreugderijkerwaard - Side channel
• Narew river restoration project
• Uilenkamp - Meander reconnection
• Warta Middle River Valley
• Enns - Aich
• Buiten Ooij - Sluice operation
• Polder Ingelheim – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Hondsbroeksche Pleij – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Bemmelse Waard – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Rhine - Polder Altenheim
• Drava - River Widening Amlach/St. Peter
• Drava - River Widening Obergottesfeld
• Drava - River Widening Rosenheim
• Rhine - Nebenrinne Bislich-Vahnum (LIFE08 NAT/D/000007)
• Meuse - Overdiepse Polder
• Rhine - Ontpoldering Noordwaard

Useful references

Bescansa P., M.J. Imaz, I. Virto, A. Enrique, W.B. Hoogmoed (2006). Soil water retention as affected by tillage and residue management in semiarid Spain. Soil & Tillage Research 87: 19–27

Bruijnzeel LA (1990). Hydrology of moist tropical forests and effects of conversion: a state of knowledge review. Paris: UNESCO International Hydrological Programe.

Hamilton L.S., Dudley N., Greminger G., Hassan N., Lamb D., Stolton S. and S.Tognetti (2008). Forests and water. FAO.

Lloyd S.D., T.H.F. Wong and C. J. Chesterfield (2002) Water sensitive urban design- a stormwater management perspective. [1]

Peterson, J.T. and T.J. Kwak. 1999. Modeling the effects of land use and climate change on riverine smallmouth bass. Ecological Applications 9: 1391-1404.

Saldi-Caromile, K., K. Bates, P. Skidmore, J. Barenti, D. Pineo. 2004. Stream Habitat Restoration Guidelines: Final Draft. Co-published by the Washington Departments of Fish and Wildlife and Ecology and the U.S. Fish and Wildlife Service. Olympia, Washington.

Other relevant information

Improving Stormwater Detention Basins for Better Stormwater Management (PEC's Stormwater Management Facility Retrofit Program. This fact sheet highlights design concepts for stormwater best management practices (BMPs) in urban areas.[2]

Watershed Forestry Resource Guide: Reducing stormwater runoff [3]