Surface Water Quantity Pathway of Change
Tuesday, May 17, 2022 5:27 AMWater(s) response to a landscape can be broadly classed into two distinct area:
- The rainfall-runoff response , i.e., the partitioning of rainfall into surface runoff and infiltration; and
- The hydraulic response., i.e., flow dynamics once water is stored and flows within a water body.
When considering the pathway of change under the first category, many of the factors considered in the chapter soil erosion will become important. Briefly this could include interception capacity of vegetation, infiltration dynamics and subsequent recharge of groundwater, surface roughness and ponding, depth of groundwater and its seasonal access characteristics by vegetation. Refer to the chapter on soil erosion to explore actions in the terrestrial ecosystem realm that could impact water quantity. It should be noted that given the distributed nature of rainfall-runoff response, interventions looking at making an impact at this is likely to be large-scale in nature (such as restoration or protection of protected areas).
A more direct change to surface water quantity is through action in or around water bodies that can modify the storage and flow characteristics. Some examples for this will include:
| Action | Description |
|---|---|
| Channel reconfiguration | Alteration of channel geometry, planform, and/or longitudinal profile and/or daylighting (converting pipes or culverts to open channels); includes meander restoration. This reconfiguration could vary from construction of a new designed state to letting the water body reclaim a configuration by removing constraints (such as letting river overtime erode the concrete channel it is enclosed in). |
| Floodplain reconnection | Practices that increase the inundation frequency, magnitude, or duration of floodplain areas and/or promote fluxes of organisms and materials between channels and floodplain areas. |
| Dam removal or retrofit | Removal of dams and weirs or modifications/retrofits to existing dams. |
| Flow modification | Practices that alter the timing and delivery of water quantity; typically, but not necessarily associated with releases from impoundments and constructed flow regulators. |
| Instream habitat improvement | Altering structural complexity to increase habitat availability and diversity for target organisms and provision of breeding habitat and refugia from disturbance and predation. |
| Lake & Wetland improvement | Improving storage capacity (such as removing excess sediment) and connectivity to restore extent of wetlands/ |
Impact of most these alterations should be quantifiable in water quantity terms (such as, change of discharge profile) immediately downstream of the intervention. In some the cases, especially when alteration is being made to flow regime by release or storage in large reservoirs, impact may be felt far downstream.