Walla Walla Basin Aquifer Recharge


 Click here for a map of Aquifer Recharge Projects


 Click here for a list of Aquifer Recharge Projects


 Click here for Near Real-time Monitoring of Aquifer Recharge Projects


 Click here for Aquifer Recharge Reports

What is Aquifer Recharge

What is Aquifer Recharge


There are two types of aquifer recharge (AR): 1 - Natural recharge and 2 - Artificial aquifer recharge.  Natural recharge is precipitation, river bed seepage, flooding and other natural forms of water that enter the groundwater system.  Artificial aquifer recharge is the enhancement of natural groundwater supplies using man-made conveyances such as infiltration basins, field flooding, infiltration galleries or injection wells.  Often, AR is conducted to improve groundwater resources (i.e. increasing storage) and is often incorporated into a broader water resource plan.

 AR  AR diagram

Why Aquifer Recharge

Why Aquifer Recharge


Groundwater systems are naturally recharged via snow melt, rain and river/lake seepage.  However, many aquifer systems (and their connected river systems) have been altered to reduce the amount of natural recharge.  Activities that can reduce natural aquifer recharge include construction of impervious surfaces (e.g. paved roads, sidewalks, etc.), development (e.g. stormwater systems that route water to rivers), levees that constrict rivers (e.g. limited floodplain connection and function) and others.  Aquifer recharge, both natural and artificial, is an important part of any sustainable aquifer system.  If there is less water being recharged to an aquifer then is being withdrawn, the aquifer will start to decline.

In the Walla Walla Valley there have been a number of water management changes that limit the amount of natural and artificial aquifer recharge.  Historically, the Walla Walla River flowed from its headwaters in the Blue Mountains into the Walla Walla Valley and then spread out into a distributary network that delivered winter and spring high flows out across the valley floor.  This distributary network provided off-channel habitat for fish and other wildlife, but also allowed for a significant amount of water to seep into the soil and  recharge the valley’s alluvial (gravel) aquifer system. The alluvial aquifer supplied water to the dozens of springs that emerge on the valley floor and provided cold water returns to the river during summer months, cooling the river and maintaining baseflows.  


Through the process of agricultural and urban development, the hydrology of the Walla Walla Basin has been significantly altered. By the mid to late 1990s, streams in the Walla Walla Basin had dry reaches during portions of late summer and early autumn, the alluvial aquifer was experiencing significant water level declines (see groundwater monitoring page), and two fish species (steelhead and bull trout) were listed as threatened under the Endangered Species Act. Irrigators, fishery agencies, the Walla Walla Basin Watershed Council (WWBWC) and many concerned citizens stepped up to address these problems. One of the solutions these parties agreed to was the decision to reduce irrigation withdrawals from the Walla Walla River by 25 cubic feet per second (cfs). This agreement created a wet river from the headwaters to mouth for the first time in a number of years, re-hydrating formerly dry reaches of the Walla Walla River in the summer. Irrigators gave up portions of their water rights to leave water instream, creating a flowing river from headwaters to mouth. To help reduced irrigation water go farther, irrigation efficiency projects were initiated across the valley. Ditches were piped, fields that were flood irrigated were switched to sprinklers/micro-sprinklers and diversion structures were updated to allow for efficient delivery and transfer of water across the valley. However, leaving water in river only fixed a portion of the water problems – the aquifer (groundwater) issues were not being addressed. The declining aquifer has caused problems for the surface water throughout the valley. Spring creeks across the valley started to decline and, in some cases, went completely dry. Overtime, groundwater levels have dropped below the mainstem Walla Walla River in portions of the valley – creating areas of high seepage loss. This causes a significant amount, sometimes up to half or more of the water in the river, to soak into the ground. Fixing the water problems in the Walla Walla Basin needs to address more than just surface water left instream. To address that point, in 2004, the WWBWC partnered with the Hudson Bay Ditch Improvement Company (HBDIC) to develop the first alluvial aquifer recharge site in the Walla Walla Valley. The purpose of this aquifer recharge was to simulate the processes of the historic distributary network by allowing winter and spring river water to be spread out across the valley and recharge the aquifer (groundwater).

Overview of AR Program

Overview of the Walla Walla Basin Aquifer Recharge Program


The Walla Walla Basin Aquifer Recharge Program involves projects in both Oregon and Washington.  Currently the programs has 18 constructed sites and funding for 2 additional sites.  14 of these projects are on the Oregon side of the border and 4 on the Washington side.  Sites within the program operate during the recharge season (November-May) assuming there are adequate instream flows in the Walla Walla River.  During the 2016 recharge season (November 2015-May 2016) the Walla Walla Basin Aquifer Recharge Program recharged a total of 7,373.19 acre-feet (2.4 billion gallons of water) to the alluvial aquifer.


Click here to learn more about the Walla Walla Basin Aquifer Recharge Program


Click here for a map of the Walla Walla Basin Aquifer Recharge Program


Basin Geology

Basin Geology


Below you can find a series of slides showing the major supra-basalt (on top of the basalt) geology units.  The slides start with the unit closest to the surface then the slides move progressively deeper underground. 


Quaternary Fine Unit (Young silts & flood deposists)


Quaternary Coarse Unit (Young/uncemented gravels)


Mio-Pliocene Coarse Unit (Old/cemented gravels)


Mio-Pliocene Fine Unit (Old silts)


Top of basalt